AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 9 - MIDI and Recording |
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Lots of hard work this week guys, with some repetition also.
1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
2. Why cannot the output of the cartridge be connected directly to a mixing console?
3. Why is it convenient to DI a synthesizer?
4. Comment on the stereo output of many synthesizers?
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
6. Comment on the use of loops in recording.
7. Comment on tape loops.
8. Comment on looping using a sampler and sequencer.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
10. Comment on the significance of synchronizing the sequencer to multitrack tape.
11. Comment on the suitability of audio sequencers for sample looping.
12. What is timecode?
13. Comment on LTC, VITC and MTC.
14. Comment on MIDI Clock.
15. Why is it desirable to synchronize two MIDI units via MIDI Clock?
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
17. Why is it desirable to synchronize a sequencer to multitrack tape?
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
19. What is an audio sequencer?
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analog or digital)?
21. Comment on the suitability of an audio sequencer for sample and loop editing?
22. Why is it not straightforward to synchronize an audio sequencer to multitrack tape?
23. What parameters of effects can often be controlled via MIDI?
24. Why would you want to control effects parameters by MIDI?
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
26. Does MTC contain an address?
27. Does MTC contain a clock?
28. Is MTC useful for synchronizing a MIDI sequencer?
29. Is MTC useful for synchronizing digital audio?
30. Is MTC useful for synchronizing analogue audio?
31. Comment on the difference between standalone hard disk recorders and computer based hard disk recorders.
32. Why is it a problem to use hard disks for long term storage?
33. Onto what media does backup/archival storage take place?
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
37. List the common digital multitrack tape formats and describe their characteristics.
38. What is 'formatting'?
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
41. Who carries out routine maintenance?
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
44. What are the effects of neglecting cleaning?
45. Why must an analogue machine be periodically demagnetised?
46. What happens if a machine is never demagnetised?
47. What might happen if the demagnetised is operated incorrectly?
48. Why do analogue tape recorders need to be lined up?
49. Do digital recorders ever need to be lined up?
50. Comment on the three elements of line up.
51. Explain the need for monitoring in sync.
52. Why is the sync signal inferior to the playback signal?
53. Why does this matter in track bouncing?
54. Is it possible to edit 2" analogue tape?
55. Is it possible to synchronise two 24-track recorders?
56. Why is it often considered better to use an integrated disk recording system rather than one that uses a personal computer as the user interface?
57. Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
58. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
59. How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
60. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
61. What information is stored in the session file?
62. Are session files usually transportable between different systems?
63. Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
64. What is 'fragmentation'?
65. Comment on archiving to CD-ROM.
66. What are 'virtual tracks'?
67. What is meant by 'edit density'? What are the implications of high edit density?
68. Does the editing and trimming of regions delete audio data from the disk?
69. In editing, what is the difference between 'slip' and 'grid' modes?
70. When might it not be possible to create a crossfade?
71. What is 'bouncing', in the context of mixing?
72. What is meant by 'latency'? What is the difference between DSP processing and host-based processing?
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It's all in the ears. - Learn the concepts not the software.
Audio Courses is a way into the music business for you
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Mon May 03, 2004 4:38 pm |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
| MIDI and Recording |
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Week 9 – MIDI and Recording
1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
The turntable is the rotating plate you place your LP’s on. The stylus is the needle that picks up the grooves on an LP. The stylus is attached to the cartridge, which transforms the information from the stylus to an electrical signal through electro-magnetic induction. The stylus and cartridge are mounted to the end of the pickup arm, which guides them through the LP. A DJ mixer is used to crossfade between two turntables that are attached to it. The mixer can also have a built-in amplifier to get the signal from the cartridge up to a workable line level. Besides that can the mixer also have EQ settings and Filters that can be applied to the sound.
2. Why cannot the output of the cartridge be connected directly to a mixing console?
The signal from the cartridge is too weak to be connected directly to a mixing console and needs to be boosted to a line level. The preamp has an RIAA EQ curve boost that gives the signal the right bass boost.
3. Why is it convenient to DI a synthesizer?
This is simpler than running the synth through an amp and then a loudspeaker and then having a microphone or two to pick up the sound. This way the sound isn’t coloured either by the room.
4. Comment on the stereo output of many synthesizers?
The stereo output on many synths don’t need to be run through an amplifier but can be plugged directly into a mixing console. Individual outputs are also available in various amounts depending on the synth. Some synthesizers also have an option of turning two individual mono outputs into a stereo out so there are one or more stereo outputs available.
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
This can be done if you want to colour the synth sound or capture the room ambiance along with the sound.
6. Comment on the use of loops in recording.
Drum loops and melody loops are used to set the groove or rhythm of a song. The drum loop could be a sample of a recognizable 2 bar loop timestretched to fit the tempo of the song and a guitar riff can be looped over it to give the basic groove of a song. Vocal phrase loops can also be used to add variation or as a chorus. The melodies and drums can of course also be played live and the best four bar section can be chosen to be looped throughout the song adding variation by taking out individual hits or making build ups.
7. Comment on tape loops.
Splicing the end and start of the tape together creates a tape loop. It is one of the oldest tricks but the playing back of the loop is still tricky. The tape must be kept in the proper relationship to the heads and cutoff sensor without benefit of the takeup or supply reels.
8. Comment on looping using a sampler and sequencer.
For example, if you have a four bar drum loop stored in the sampler, timestretched to the tempo of the sequencer and want to loop it in the sequencer, then it should be triggered at the beginning of every fourth bar to give a continuous loop.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
To put it simply, it is easier. If a sample was to be looped in the sampler, then you would have to decide how many times you want the sample to loop and set the number. This uses up more DSP power in the sampler and if you want to have a break where the sample isn’t playing, then you’ll have to set a new number of times the sample should loop when it is re-triggered. In the sequencer, you just have to trigger the sample after the last bar of the sample.
10. Comment on the significance of synchronizing the sequencer to multitrack tape.
The significance of synching the sequencer to multitrack tape is to insure that everything will be played back together in sync. The MIDI voices and the recorded drums or vocals on the multitrack should blend together without delays in timing. This can be done with SMPTE/EBU or MTC.
11. Comment on the suitability of audio sequencers for sample looping.
Using an audio sequencer to loop a sample can have its benefits. Firstly, there’s the visual aspect. You get to see the loops. Another benefit is that since the sample is copied over and over and not just re-triggered as it is in a sampler when looping, any part of the sample can be individually edited from loop to loop by cutting, trimming, reversing or panning etc. This gives greater editing abilities and options and adds more variation to the sample throughout the song. It is possible to remove individual drum hits within the sample to add breaks. This is not possible to do when triggering from a sampler.
12. What is timecode?
Time code is a way of synching two or more pieces of audio/video equipment together to get them to play in sync with each other. The industry standard for video equipment synchronisation is the SMPTE/EBU (Society of Motion Picture and Television Engineers)/(European Broadcasting Union) time code. Time code syncs all equipment that is in the system to a real-time 8-digit 24-hour clock.
13. Comment on LTC, VITC and MTC.
LTC (Longitudinal Time Code)
This is the Audio Sync Tone version of SMPTE and requires a dedicated audio track for itself since the time code is recorded as a waveform tone along the length of the tape. The tone should not be recorded at a too high level as distortion can lead to errors in the signal. And if the signal is recorded too low, cross talk can contaminate the signal and drop it out of sync. The signal is recorded using a Bi-Phase Mark method where the binary 1 of the signal has two transitions instead of one because the ‘on’ and ‘off’ states of binary 0’s and 1’s can’t reliably be distinguished when passing through a channel designed for analogue audio signals. LTC cannot be read when the tape is not playing or if it is playing at slow speeds, only at normal or higher speeds. It is also suitable for both audio and video synching.
VITC (Vertical Interval Time Code)
This is another version of the SMPTE and is used for video and is incorporated into the video signal during the initial recording or while copying tapes. It is inserted into the vertical sync period of the video frame making it able to be read while the tape is paused. It is a part of the videotape and can be read at normal or slower speeds.
MTC (MIDI Time Code)
MIDI equipment can be synched together to an absolute timing reference using the principals of SMPTE. This is called MIDI Time Code. MTC is an accepted standard for synchronising musical equipment.
14. Comment on MIDI Clock.
MIDI Clock messages are imbedded in MIDI data and carry timing information. The Clock messages are sent from the master device to the connected slave device(s) and run at a rate of 24 pulses per quarter note.
15. Why is it desirable to synchronize two MIDI units via MIDI Clock?
This is desirable because it keeps the two MIDI units in sync and the master unit sends messages to the slave unit about the tempo/timing of the song and the position so the two units are in sync at any starting position in the song and even when the tempo is changed on the master unit.
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
While MIDI Clock syncs with slave units using the tempo and beats and bars, MTC is independent of the musical tempo and follows the same format as SMPTE by using real time and frames instead of beats and bars. MIDI Clock messages don’t carry positioning information with the sync so if a pulse gets lost, there will be a one-pulse delay between the master and slave devices. MTC carries positioning data continuously to make up for differences that might occur. This positional data is sent in short burst (four per frame). It takes 8 of these messages to complete the positioning data meaning that the receiving MIDI device needs to read two frames before it gets the complete positioning information. So the positioning information is updated every two frames.
17. Why is it desirable to synchronize a sequencer to multitrack tape?
It is desirable to sync a sequencer to multitrack and not the other way around because it’s easier to find your way around when working from the sequencer than from the multitrack.
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
The first stage would be to get some voices recorded into the sequencer. You should build up your MIDI composition and have it sequenced out on the sequencer so it starts to look like a song. Assuming that you have got the tape striped and everything has been taken into account such as tempi then the second stage would be to record the tracks over to the multitrack from the sequenced material in the sequencer. If the first track is the drum track and the module or sampler producing the sound doesn’t have the drum parts mapped to individual outputs, or doesn’t have individual outputs, then each drum part needs to be recorded over separately to its own track. When all the tracks available on the multitrack have been filled, then more voices can be played from the MIDI sound module in real time through the sequencer and would of course be in sync with the material on the multitrack.
19. What is an audio sequencer?
An audio sequencer is a piece of software in which audio can be recorded, edited, mixed and sequenced to make a finished song. Software like this usually comes with the ability to MIDI sequence as well and professional editing options. Some software examples are Logic, Cubase SX and Nuendo.
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analogue or digital)?
Yes it is a suitable replacement for a multitrack tape recorder if it is bundled with a multichannel soundcard capable of recording multiple tracks simultaneously.
21. Comment on the suitability of an audio sequencer for sample and loop editing?
Answered in question 11.
22. Why is it not straightforward to synchronize an audio sequencer to multitrack tape?
This is because the tape has to be striped first, meaning it has to have the time code recorded on to it before it can be synched. When recording the time code, the level of it has to be around 7 dB to 5 dB below 0 and it can sometimes be difficult to get this level. If you need to put the cable through the mixer first to monitor the signal level, you have to make sure no cross talk is recorded with the signal plus that no EQ or effects (compressors/reverbs) are applied to the channel carrying the time code. Then there also has to be 2 bars left empty at the beginning of the sequence. One to make sure the sequencer ‘catches up’ with the recorder since some sequencers may take some time to get started, and the second bar is for a 4 beat metronome count in.
23. What parameters of effects can often be controlled via MIDI?
The parameters of effects that can be controlled via MIDI include amount of reverb or other send effects, panning and EQ’ing.
24. Why would you want to control effects parameters by MIDI?
There may be different sections of a song that need separate amounts of reverb on the vocals or maybe a sound effect needs to be panned left to right. Instead of having to fiddle with these parameters manually every time you play back the mix, they can be controlled by MIDI and recorded in as automation and will automatically adjust when played back.
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
Yes, MTC comes in all four frame rates of 30 fps, 29.97 fps (30 fps drop frame), 25 fps and 24 fps.
26. Does MTC contain an address?
Don’t know, does it?
27. Does MTC contain a clock?
No it does not.
28. Is MTC useful for synchronizing a MIDI sequencer?
Yes it is.
29. Is MTC useful for synchronizing digital audio?
Yes it is.
30. Is MTC useful for synchronizing analogue audio?
No, I don’t think MTC is even used to sync analogue audio.
31. Comment on the difference between standalone hard disk recorders and computer based hard disk recorders.
Standalone hard disk recorders have a dedicated hard drive, software and effects processors for the audio recording, editing and mixing. They are ‘right out of the box’ pieces of hardware, meaning they are ready for use right away and are also more portable than a stationary computer. The computer has to be equipped with the professional multi-channel soundcard to be able to work with multiple simultaneous audio streams and the computer may also have to be upgraded in order for it to function properly when handling lots of audio. Third-party software including sequencers and effects are easier to integrate on a computer than, if at all, on a hard disk recorder.
32. Why is it a problem to use hard disks for long-term storage?
Hard disks are unstable and it would be risky to use them for long-term storage.
33. Onto what media does backup/archival storage take place?
Zip Drives, Magneto Optical, CD-ROM’s, Floppy Disks
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
Any edits done on a standalone hard disk recorder can easily be undone. There is a visual display of the editing taking place and everything is virtually non-destructive. When cutting tape, there is no such luxury and you only have one chance at getting the edit right.
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
Advantages
More upgrading options
Third-party software integration
Disadvantages
Less portable
Not ‘right out of the box’
Not dedicated to audio work
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
Multitrack audio data can be transferred into Pro Tools for editing and adding effects and then bounced out to the multitrack again. The multitrack could also be used as a backup storage device.
37. List the common digital multitrack tape formats and describe their characteristics.
DASH (digital audio stationary head)
The 24-track DASH machines are two-way compatible with 48-track DASH machines, meaning the same tape used to record the 24 tracks of digital audio on the 24-track machine can be used to record the remaining 24 tracks of audio on the 48-track DASH. Tracks 25-48 are recorded in the spaces left in between the 24 tracks by the 24-track DASH machine. If the tape is then played back on a 24-track DASH after it is filled with 48 tracks, only the tracks recorded on the 24-track DASH are played back.
MDM (modular digital multitrack)
Modular digital multitracks have 8 tracks per unit but more tracks can be obtained by linking multiple machines together by using their internal time code. There are two types of MDM’s, which are the ADAT and the DTRS.
ADAT is less expensive than DTRS machines so they are more likely to be found in budget or home studios. A 2-hour ADAT tape, which is S-VHS, can hold about 40 minutes of audio. ADAT machines work in 20-bit resolution.
A DTRS hi-8 8mm 2-hour tape can hold about 108 minutes of audio. Some models can reach 24-bit resolution. The DTRS machines are preferred for post-production work over ADAT machines because they locate faster.
38. What is 'formatting'?
Formatting is the process of erasing everything that is on a digital storage medium (i.e. formatting a hard disk)
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
Digital multitrack will suffer no generation quality loss when copying. It is an easier job to edit a digital multitrack tape than an analogue tape. A disadvantage a digital multitrack would have is that it doesn’t have the warmth that analogue tape compression adds to recorded data.
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
A digital recorder can be cleaned using a special cleaning tape where as an analogue recorder needs to have its heads aligned, cleaned and be demagnetised. The analogue recorder needs more constant care than the digital recorder.
41. Who carries out routine maintenance?
A qualified technician should be in charge of routine maintenance.
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
The heads can be cleaned using denatured or 91% isopropyl alcohol on a cotton swab. This is done by dipping the swab in the alcohol and wiping the heads.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
Denatured alcohol is suitable for cleaning the pinch roller of an analogue machine. Make sure the cotton swab isn’t wet but only damp to insure the alcohol doesn’t run and gets into the bearings.
44. What are the effects of neglecting cleaning?
Neglecting cleaning the analogue recorder will result in deteriorating sound quality. The tape needs to be in very close contact with the heads so they need to be cleaned probably once before every session.
45. Why must an analogue machine be periodically demagnetised?
This is done to avoid magnetism build up, which can result in tapes not recording properly and being erased.
46. What happens if a machine is never demagnetised?
This can result in the tapes being erased when used with the recorder.
47. What might happen if the demagnetised is operated incorrectly?
The heads may get even more magnetised instead of being demagnetised.
48. Why do analogue tape recorders need to be lined up?
Analogue tape recorders need to be lined up to insure that they are working optimally and that any tape recorded on the recorder will play back properly on another recorder.
49. Do digital recorders ever need to be lined up?
The DASH machine needs to be aligned every six months by a qualified specialist using a laptop.
50. Comment on the three elements of line up.
The azimuth or the relative angle of the head to the tape needs to be lined up perpendicular in order to insure optimal frequency response. If they aren’t aligned properly the HF can suffer.
Adjusting the bias is done to find the optimal balance between distortion, noise and maximum output level.
The recording and playback levels are adjusted to standard levels. This is done for both LF and HF.
51. Explain the need for monitoring in sync.
If monitoring wasn’t done in sync then the overdubbing would not be playing in time with the rest of the recorded material. Since the recording head and playback head are a few inches apart, synching the monitoring is needed to prevent delay.
52. Why is the sync signal inferior to the playback signal?
This is because the recording head is not optimised for playback.
53. Why does this matter in track bouncing?
Because bouncing from the inferior recording head signal will give a loss in the quality of the audio.
54. Is it possible to edit 2" analogue tape?
Yes, by cutting it and pasting it back together physically.
55. Is it possible to synchronise two 24-track recorders?
I would think so, yes.
56. Why is it often considered better to use an integrated disk recording system rather than one that uses a personal computer as the user interface?
The integrated disk recording system would be 100% dedicated to audio recording and editing where as a personal computer is not. The integrated disk recording system is usually more portable because it is normally one piece of hardware where as a PC would not be as portable and has more hardware pieces.
57. Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
Disk recorders don’t use tape so no tape heads have to be aligned nor does any tape have to be purchased since the audio data is stored directly on the hard disk. Hard disk audio data is also quicker accessible than audio on tape and hence, quicker to edit. The price of a hard disk recorder is also less than an analogue tape multitrack.
58. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
It will have 24 tracks. The 24 outputs can be connected to an analogue console for individual mixing and editing of the 24 recorded tracks.
59. How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
To act as a full replacement for a 24-track tape recorder, a disk recorder would need to have 24 inputs and 24 outputs.
60. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
With only two inputs, it would not be possible to multitrack stereo data and only two mono sources could be tracked simultaneously. This would make the recording process tedious if 24 mono sources are to be tracked. With only two outputs, all audio data would have to be mixed inside the recording system since no individual outs can be routed to effects modules or a console.
61. What information is stored in the session file?
A session file stores the title of the project, fader positions, automation, the edits done to audio files, effects settings such as EQ, Send/Return, the arrangement of all recorded audio etc. Basically, it stores your mix exactly the way you left it the last time you saved.
62. Are session files usually transportable between different systems?
If the different systems are using the same software workstations with the same plugins, the session files are usually transportable and this is beneficial when many people are working on the same project or if you are on the go, then you can work on a project on a laptop and then transport it to a stationary computer for final mixing. There could be some problems if the different systems have different inputs and outputs, for example if you’re working on a Pro Tools TDM system with 16 ins and outs and have assigned outputs and then transport the session to a Pro Tools Digi001 system, which only have 8 outputs, but why would you need to do this? If you transport a Pro Tools session it would usually go from a low cost Lite edition to the expensive one. For example, you could take a pre production session done at home on a Pro Tools LE system like Digi001 or Digi002 and after audio has been recorded and arranged, it can then be taken to a professional studio equipped with a Pro Tools 24 mix plus or TDM system and since they would have the same amount or more outputs than the Lite systems, there shouldn’t be any big complications in the transport. Of course, complications can occur but if everything is taken into consideration, this can be very beneficial.
63. Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
SCSI disks can either be internal or external and many can be daisy chained together. Are fast and reliable.
ATA disks are not the fastest but are cheap. They cannot be independently external but can be used in a removable cartridge and then connected to a host computer via Firewire.
Firewire is a very fast, hot swappable data transfer interface. It is not a disk in itself but as described above, an ATA hard disk can be enclosed in a cartridge and then be used as an external drive connected via a Firewire cable.
64. What is 'fragmentation'?
A disk is fragmented if a disk cannot assign contiguous disk space to incoming data. This causes the disk mechanism to work harder to find space and can limit the number of simultaneous audio tracks that can be recorded. A disk can get fragmented if it is nearly full or hasn’t been completely erased in a long time. This is why a separate disk drive used exclusively for audio files is recommended. The drive can be used to record and edit audio data and can be periodically formatted.
65. Comment on archiving to CD-ROM.
CD-ROM archiving is a very stable and reliable method, taken that the CD-ROM’s are taken care of and stored in a safe place. The downside is the small amount of space available on a CD-ROM (700 MB).
66. What are 'virtual tracks'?
If a hard disk recorder has, for example, a limit of only 8 physical tracks of simultaneous playback, it doesn’t necessarily mean that no more tracks can be stored on the hard disk as ‘takes’. These are stored on virtual tracks and the number that can be stored depends on the recorders specification. The virtual tracks can then be switched with the real tracks.
67. What is meant by 'edit density'? What are the implications of high edit density?
When you have edited audio and cut it into segments, the disk drive has to work a little harder to retrieve the data when playing it back since it is not contiguous due to the editing done. ‘Edit density’ is a term used to refer to the number, length and proximity of regions. High edit density would mean that a lot of editing has been done and that there are short, densely packed regions. This means that the disk has to work even harder to retrieve the data and this can affect the number of tracks that can be played back simultaneously.
68. Does the editing and trimming of regions delete audio data from the disk?
No, the trimmed out regions of audio is not deleted from the disk but silenced and a full length unedited version of the audio should be available in the audio pool.
69. In editing, what is the difference between 'slip' and 'grid' modes?
In grid mode, moving an audio region back or forth will automatically snap it into place to the closest line in a defined grid (bars, beats, quarter bars…). If the sequencer is in slip mode, the region will not snap into place but stay, as is, exactly where it has been moved
70. When might it not be possible to create a crossfade?
If two regions of audio are not overlapping, it will not be possible to crossfade them.
71. What is 'bouncing', in the context of mixing?
It means taking selected audio tracks and mixing them down to one stereo track. In the context of mixing, it means taking the entire mix and bouncing it to the hard disk as one stereo file. This eliminates having to record the mix over to another medium when mixing down.
72. What is meant by 'latency'? What is the difference between DSP processing and host-based processing?
Speaking in terms of recording vocals, latency is the time it takes from when something is said into the microphone to when it reaches the ears by travelling through the audio hardware and back out the headphones. If a delay is heard, it can be because of high latency, which is due to a large buffer size set in the sequencer. The difference between DSP (digital signal processing) and host-based processing is that DSP does not put a strain on the computers processor since it doesn’t utilize it. DSP chips are specifically designed for audio so the latency is always low (about 3-4 ms). |
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Wed May 05, 2004 6:49 pm |
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hoggs33
Joined: 09 Feb 2004
Posts: 55
Location: Nottingham, England |
| MIDI and Recording |
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What a lot of questions! – here are my answers – struggled to find some resources particularly on some of the MIDI sync stuff – a few vague answers are therefore in evidence!
1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
The cartridge is the device that changes the mechanical vibrations stored on records into electrical signals. The stylus is the needle part of the cartridges that is in contact with the grooves of the disc..
The pick up arm is what the cartridge and stylus is attached to and hold them in place in the grooves of the record.
A turntable is a device to support and rotate a record during playback
The mixer would be used to mix the output from each of the turntables/decks used.
2. Why cannot the output of the cartridge be connected directly to a mixing console?
As the signal from the stylus is not loud enough for recording it the output could not be connected directly to a mixing console therefore it would need to be connected using a pre amp to ‘boost’ the signal.
3. Why is it convenient to DI a synthesizer?
It eliminates the need to use a separate amp which would then need to be mic’d up. It also gives a better sound which may be lost by incorrect micing as the stereo output from the synth is recorded ‘directly’
4. Comment on the stereo output of many synthesizers?
The majority of synths today have both stereo outputs and assignable outputs which gives more flexible options for connecting to a desk when using internal effects from the synth when wanting to try out a particular sound or effect but do not want to commit it to tape.
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
To get a more ambient or live sound as a direct input could sometimes sound a bit lifeless.
6. Comment on the use of loops in recording.
Loops are used quite frequently now in recording, particularly in dance music where for example a breakbeat loop may be sampled and looped over and over again to create a drum track. This provides a very quick and easy way to create a song.
7. Comment on tape loops.
Tape loops are created by splicing the end of a piece of tape to its beginning – somewhat more time consuming than creating loops with sequencers or samplers.
8. Comment on looping using a sampler and sequencer.
A sampler would play a loop over and over again by re-triggering the sample each time a key was pressed. A sequencer uses one instance of the loop which is then copied the required number of times.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
It is likely to be easier to get the loop running more smoothly in a sequencer once any timing and bpm problems have been rectified as it is easier to edit the original sample to prevent iny click as the sample loops.
10. Comment on the significance of synchronizing the sequencer to multitrack tape.
See question 17 below – think I pretty much answered this one there.
11. Comment on the suitability of audio sequencers for sample looping.
Audio sequencers can be used fro sample looping although they work best with short sample such as individual drum hits which can be placed in the correct place on the track and then copied to repeat the patterns. Limitations however do arise with sampled breakbeats for example when problems can arise with the tempo. The bpm of the original needs to be ascertained so that the loop repeats itself correctly.
12. What is timecode?
Timecode was originally devised to enable video editing to be carried out by copying from one machine to another, rather than cutting the tape as had been done previously. Timecode therefore relates very closely to the concept of frames, and also to the precise timing required to make video editing possible.
Timecode encodes data identifying numbers together with a stable and regular clock pulse, into a signal that audio recorders see just as another audio signal. It can therefore be recorded by any type of audio recorder. It contains two components – the address which identifies individual frames of video in terms of hours, minutes, seconds and frames and the clock which I sthe regular timing of the data pulses which give a regular signal by which the speed of playback can be measured.
13. Comment on LTC, VITC and MTC.
LTC is longitudinal Timecode, VITC is Vertical Interval Timecode and MTC is MIDI Timecode.
MTC is SMPTE/EBU Society of Motion Picture and Television Engineers/European Broadcasting Union) timecode adapted for use in a MIDI system. SMPTE/EBU timecode identifies each frame of a video recording with a unqiue number in terms of hours, minutes, seconds and frames. This is called the address. It also contains a clock pulse so that the running speed of two pieces of equipment can be compared and controlled so that they always run in sync. SMPTE/EBU timecode in the form of LTC is recorded as an audio signal carrying data. MTC uses the address part of SMPTE/EBU timecode, but not the clock. MTC messages are sent four times per notional video frame, at a constant, non-tempo related rate and eight are required to build up a complete frame address. VITC can be read in still frame mode, LTC cannot
14. Comment on MIDI Clock.
MIDI clock is time data in the MIDI signal that advances one step each 1/24 of a beat and can be used to sync two sequencers together.
15. Why is it desirable to synchronize two MIDI units via MIDI Clock?
One would be a master and the other a slave and would sync together much better than using other methods without one ‘drifting’ out of time with another.
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
In order for MIDI based devices to operate on absolute time code which is independent of tempo, MTC must be used. Existing devices translate SMPTE into MIDI clocks and Song Position Pointers based upon a given tempo. (Not sure if I have really answered the question here)
17. Why is it desirable to synchronize a sequencer to multitrack tape?
To enable a song arrangement to be built up using a MIDI sequencer system. The arrangement would be started off in the sequencer and the basic tracks built, then copied to the multitrack tape. If the sequencer is then synchronized to the tape, any MIDI sound modules are freed up and more layers of instrument sounds can be created and recorded in sync with the original.
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
The process would start with a MIDI sequencer, keyboard and sound modules. Sufficient tracks would be recorded to comprise the basic tracks of the arrangement. Once this is done, a reel of tape is loaded and striped with timecode. The output of the timecode track is connected to the syncronizer, which will convert it to MTC. This is then fed to the MIDI IN of the sequencer.
19. What is an audio sequencer?
An audio sequencer records sections of audio rather than MIDI data. This data could be short samples such as individual drum hit, breakbeats – two or four bar phrases for example or lengthy recordings, similar to tape recording.
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analog or digital)?
In this respect I am thinking primarily of a computer based software sequencer. I would think they have made huge steps towards being able to replace multitrack tape recorders over the last few years but would not think they would be a suitable replacement just yet. There are of course compatibility issues between different systems, likely to be latency issues and performance issues. However as technology progresses I feel they may become more suitable as a replacement.
21. Comment on the suitability of an audio sequencer for sample and loop editing?
Software audio sequencers provide the perfect environment for sample and loop editing as it is possible to see the waveform in great detail and zoom in on certain sections. Also many sequencers have the ability to time stretch and sync loops with the bpm of the track.
22. Why is it not straightforward to synchronize an audio sequencer to multitrack tape?
If there is no MIDI on the track then timing codes will not be present. Not really sure on this one?
23. What parameters of effects can often be controlled via MIDI?
You could change any parameter of an effect via MIDI such as decay times on a reverb effect and other things such as pan and volume.
24. Why would you want to control effects parameters by MIDI?
They would be ‘non-destructive’ and therefore could be adjusted or removed as required.
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
Not sure on this one.
26. Does MTC contain an address?
Yes, it uses the address part of SMPTE/EBU timecode.
27. Does MTC contain a clock?
No.
28. Is MTC useful for synchronizing a MIDI sequencer?
Yes
29. Is MTC useful for synchronizing digital audio?
Yes
30. Is MTC useful for synchronizing analogue audio?
Yes
31. Comment on the difference between standalone hard disk recorders and computer based hard disk recorders.
Standalone hard disk recorders are purpose built for the job and therefore in theory should perform the job better. A computer based system may not have been specifically designed for music which can affect performance. Hard disk recorders are likely to have better connectivity to outside equipment such as effects and mixing desks. Computer based system however to provide a lot more flexibility with numbers of tracks and effects etc and particularly editing is somewhat easier on a computer based system as you can actually see what you are doing on a screen.
32. Why is it a problem to use hard disks for long term storage?
In this respect I assume you mean hard disks within a computer or on a stand alone system. Such disks can become unstable and crash resulting in loss of data. They can be prone to magnetic fields and as it is a fairly new system of storage their longevity has not yet really been tested. They are also likely to cost more per MB than say storing on a DVD.
33. Onto what media does backup/archival storage take place?
DVD, CD, Zip drive, Minidisc, flash memory cards etc.
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
Editing is much easier as it is all done within the ‘box’ and does not involve splicing tape etc – once this has been done there is no going back. Hard disk recorders usually allow any edits to be undone giving much more flexibility. It is also easy to copy and paste sections of audio that are repeated thus cutting down on overall recording time.
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
Computer based systems are likely to be more prone to crashing and contain many different parts from various manufacturers which can effect reliability and quality. Computer based systems however do have the benefit of being able to add many cheap and even free effects and synths and offer better scope for expandability. Computer based systems to provide a visual display of the recording (although this is available with some stand alone recorders).
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
Not really sure but assume pro tools could be used to edit tracks which can then be recorded to tape.
37. List the common digital multitrack tape formats and describe their characteristics.
DAT, DASH, ADAT & DTRS
38. What is 'formatting'?
Preparing a disk for use in a particular system. Formatting can also be used to erase a disk if required.
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
With analogue recorders – once recorded, all the tracks have a fixed relationship in time, In a digital recorder, it is easy to move one track backwards or forwards in time, or copy it to a new location in the song. In general digital recorders do give much greater flexibility and ease of editing. Some may argue however that analogue still gives a warmer ‘real’ sound. Some also argue that analogue recording are easier to mix. Also tape is ‘universal’ and so can be played on any tape machine whereas there are likely to be compatibility issues with digital recordings between different manufacturers and systems.
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
The most you can do with a digital recorder is run a cleaning tape through it. Analogue recorders do require specific cleaning tasks to be carried out on a regular basis, otherwise performance will suffer. Analogue machines do therefore require much more care, cleaning and maintenance than digital recorders.
41. Who carries out routine maintenance?
Some routine maintenance can be carried out by the studio owner or staff. However items such as demagnetising does require training. Ideally all maintenance should be carried out by a specialist.
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
The heads and all metallic parts of the tape contacts are cleaned gently with a cotton bud dipped in isopropyl alcohol. This has very good cleaning qualities.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
The pinch roller is made up of a rubbery plastic and ideally should not be cleaned with isopropyl alchohol but it often is. You should use a special rubber cleaner for the job.
44. What are the effects of neglecting cleaning?
The overall performance of the machine will deteriorate.
45. Why must an analogue machine be periodically demagnetised?
If not demagnetised, the metal parts will collect a residual magnetism that will partly erase any tape that is played on the machine.
46. What happens if a machine is never demagnetised?
See answer to question 45 above.
47. What might happen if the demagnetised is operated incorrectly?
The condition could be made even worse.
48. Why do analogue tape recorders need to be lined up?
To get the best out of the machine and tape and to make sure that a tape played on one recorder will play properly on any other recorder.
49. Do digital recorders ever need to be lined up?
Not sure but would guess that they don’t.
50. Comment on the three elements of line up.
The three elements of line up are Azimuth, Bias and EQ.
With Azimuth the heads need to be absolutely vertical with respect to the tape otherwise there will be cancellation at high frequencies. The Bias level needs to be set to optimize distortion, maximum output level and noise. The EQ is set as follows:-
High frequency playback EQ – the 10kHz tone on the calibration tape is played and HF EQ adjusted. For the record level, a 1kHz tone at the studio’s standard electrical level is recorded onto a blank tape and the record level adjusted fro unity gain. Bo the high frequency and low frequency record EQ’s are set fro a flat response.
51. Explain the need for monitoring in sync.
This is so that the person performing an overdub can listen to the playback and then play their part in sync with the original.
52. Why is the sync signal inferior to the playback signal?
While overdubbing, the record head is used as a playback head in order for the parts to be in sync. The sound quality is not as good therefore as the record head is optimized for recording and not playback.
53. Why does this matter in track bouncing?
If not used then the bounce will not be in time with the other tracks.
54. Is it possible to edit 2" analogue tape?
Yes – the tape is placed in a special precision-machined aluminium editing block, and cut with a single sided razor blade, guided by an angled slot.
55. Is it possible to synchronise two 24-track recorders?
Yes, but only if the machines are identical mechanically – in this instance, a wax pencil mark could be made on corresponding rotating tape guides and the tapes then backed up by the same number of revolutions.
56. Why is it often considered better to use an integrated disk recording system rather than one that uses a personal computer as the user interface?
With an integrated disk recording system, the entire system is a known quantity to the manufacturer, who can guarantee performance. If there is a problem, you just go back to the manufacturer for the solution
57. Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
The Euphonix R-1 is marketed as a replacement for the traditional multitrack recorder. The IZ RADAR and other similar machines are ‘drop in’ replacements for the old 24 track recorders. Pro Tools is far and away the most common professional system.
58. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
24
59. How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
24
60. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
No more than 2 tracks could be recorded simultaneously and the output would only be the main stereo out – this restricts the use of external effects units and routing to a mixing desk etc.
61. What information is stored in the session file?
Project title, audio files used, edits, track assignments and mix and plug in data.
62. Are session files usually transportable between different systems?
Not usually as session files on different systems are highly incompatible between manufacturers.
63. Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
SCSI is commonly regarded as an old interface on the verge of extinction. However SCSI does allow disk to be external to the computer (the host), and disks can be daisy chained on a bus so that several can be connected at the same time. It also has the advantage that, being a parallel interface, data travels along several wires rather than the single data conductor of Firewire or USB and can therefore be faster than either.
ATA disks are cheap, but they are not the fastest. The ATA interface does not intrinsically lend itself to having disks that are external to the computer so expansion of storage capacity is limited. Some systems allow the ATA disk to be installed in a removable cartridge, which does come close to the convenience of tape.
Firewire is a fast serial interface, meaning that data travels along only one conductor the Firewire cable. It is self-configuring – no ID numbers are set by the user, it is hot swappable between machines, it can use bus power – i.e transfer power down the cable with the need for an external power supply and it uses thin, flexible cable with robust connectors.
64. What is 'fragmentation'?
A condition in which pieces of individual files on a disk volume are not contiguous, but rather are broken up and scattered around the disk. This means the disk has to work harder to find the data when playing back audio for example which can have an adverse effect on performance.
65. Comment on archiving to CD-ROM.
CD-ROM’s can only store a relatively small amount of data (around 700Mb). Audio data takes up a lot of memory so this could cause problems. Also long term storage of data on CD ROM’s has not been tested yet as it is a relatively new format for storage – the discs could therefore deteriorate over time – particularly cheaper discs.
66. What are 'virtual tracks'?
Hard disk recorders can store additional tracks that are in sync with the regular tracks but cannot be allocated to an output.
67. What is meant by 'edit density'? What are the implications of high edit density?
Edit density is the number of regions, their length and proximity to each other and how far they are physically separated on the disk. The greater the edit density, the fewer tracks will play.
68. Does the editing and trimming of regions delete audio data from the disk?
No the audio data is just silenced.
69. In editing, what is the difference between 'slip' and 'grid' modes?
Since there is no fixed time relationship between tracks on a hard disk recorder, any track or region can be ‘slipped’ with respect to the others. This would be carried out in slip mode.
Grid mode is when a grid is defined so that regions will always ‘snap’ to grid positions when moved.
70. When might it not be possible to create a crossfade?
In order to create a crossfade there has to be audio on the disk that extends beyond the region boundaries. This material is used to create the crossfade. If there is no material beyond the region boundaries, or insufficient for the desired duration of the crossfade, then the crossfade cannot be created.
71. What is 'bouncing', in the context of mixing?
The mixing together of similar tracks, such as backing vocals, onto fewer tracks to free up the original tracks for further recording.
72. What is meant by 'latency'? What is the difference between DSP processing and host-based processing?
Latency is the delay in a sound being heard. For example the time between a key being pressed on a keyboard and the sound actually being heard.
Host based processing is where the computers own processor performs any ‘calculations’ such as those required for plug in effects. In DSP processing (direct signal processing) audio signals are different in structure from standard computer data and benefit from having DSP chips specially designed for the purpose. Special DSP cards are used to perform mixing and plug in effects resulting in less demand on the computers CPU and lower latency. |
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Thu May 06, 2004 7:03 pm |
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griff505
Joined: 23 Feb 2004
Posts: 68
Location: Bristol |
Hey Chris,
What was the name of the microphone you recommended to me a while back? It was similar to the Rode NT-3, but seemed to be better value for the money.
I hope to sell my NT-3 and get two of the recommended one to use as a stereo pair.
Thanks,
Mark. |
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Sat May 08, 2004 6:48 pm |
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griff505
Joined: 23 Feb 2004
Posts: 68
Location: Bristol |
| MIDI and Recording |
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1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
Cartridge – The cartridge holds the stylus and transforms vibrations into electrical signals using electro-magnetic induction.
Stylus – The stylus has contact with the vinyl. It ‘reads’ information from the grooves of the vinyl and vibrates accordingly.
Pickup arm – The cartridge is attached to the pickup arm which freely follows the grooves of the vinyl.
Turntable – A rotating plate which turns the vinyl in order for the stylus to pick up information from the grooves of the vinyl. Its speed can be varied according to the requirements of the vinyl.
Mixer – Used to control the outputs of multiple turntables. It can control crossfade, volume levels, and eq. Mixers may also include an amplifier to increase the output from the turntable to line level.
2. Why cannot the output of the cartridge be connected directly to a mixing console?
The output from a cartridge is too weak to be connected directly to a mixer; therefore a pre-amp is required to boost the signal to line level. Also, to achieve a satisfactory duration on a record, RIAA EQ is used in the cutting process which reduces LF and therefore the maximum excursion of the groove. This is compensated by reverse RIAA EQ in the cartridge input stage. Normal mic and line inputs do not have this.
3. Why is it convenient to DI a synthesizer?
To avoid the colouration which would be created by connecting a synth to an amp and speaker, and then using a stereo miking technique to mic up the speaker.
4. Comment on the stereo output of many synthesizers?
Synths stereo outputs can be connected directly to an amplifier at line level. Multi-timbral synths often have more than one set of stereo outputs to allow different sounds to be connected to different mixer inputs and recorded to separate tracks, simultaneously.
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
This technique could be used to add some colour to the sound of the synth. Miking techniques could be used to capture the sound and ambience of the room. Special effects could also be achieved by miking the synth up to special speakers, for example a rotating Leslie Cabinet.
6. Comment on the use of loops in recording.
Loops are used in various types of music. Early experimental electronic composers used tape loops, often manipulated to create Musique Concrete pieces. Today loops are used in experimental music, and mainstream dance music – mostly drum loops – either cut and paste in a sequencer, or triggered by a sampler.
7. Comment on tape loops.
Tape loops are loops of pre-recorded magnetic tape used to create repetitive, rhythmic musical patterns. A measure of recorded magnetic tape is cut and spliced to end to end, creating a circle or loop which can be played continuously. Simultaneous playing of tape loops to create phase patterns and rhythms was developed and initially used by Musique Concrete and Tape music composers, and was utilized by Steve Reich and Karlheinz Stockhausen. Tape looping is in some ways a precursor of digital sampling.
8. Comment on looping using a sampler and sequencer.
A sample of set length, or set of samples, can be loaded into a sampler. The sample can then be programmed to be triggered by the sequencer as they are required. For example, if it was a drum loop it would need to be cut to a certain amount of bars, and then triggered on every multiple of the length of the loops by the sequencer.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
It is easier to loop a sample using a sequencer as it can be easily visualised, different loops can be programmed to play, and the exact length of the sample is not so important as it can be triggered every bar.
10. Comment on the significance of synchronizing the sequencer to multitrack tape.
Synchronising the sequencer to multitrack tape allows everything to play back in sync with each other. Sounds controlled my MIDI and the sound on the tape should be perfectly aligned, with no delay or latency. SMPTE is often used to achieve this.
11. Comment on the suitability of audio sequencers for sample looping.
Sequencers are very well suited for sample looping, it is easy to visualise the loops, it is easy to cut, paste and edit the loop or individual loops, and it is easy to change eq and effects settings.
12. What is timecode?
Timecode is a signal that contains a chronological record of the absolute time in a recording. It is used for synchronizing different recorders. It can be used for electronic editing. Timecode was initially invented for the motion picture business, as a method of synchronizing the pictures recorded in the frames of a camera to the sound recorded on tape recorder.
13. Comment on LTC, VITC and MTC.
LTC - Longitudinal Timecode - Longitudinal time code is a timing signal that is part of an audio tape recording. It is recorded on a track that runs lengthwise along the tape, which is why it is called longitudinal. LTC assigns a specific time in hours, minutes, and seconds to various points along the tape. The LTC can therefore be used to keep a playback machine synchronized with a master time source. This can be useful in broadcasting applications where program lengths and time-slot scheduling are critical. Because the timing signal is recorded lengthwise along the tape, it is necessary for the tape to be in motion for the signal to be read.
VITC - Vertical Interval Time Code - A timing signal that is part of a video recording. It is recorded in the vertical blanking intervals between successive picture frames, hence the "vertical interval."
VITC is one of two timing schemes adopted by the Society of Motion Picture and Television Engineers (SMPTE) in the 1960s. The other, known as longitudinal time code (LTC), is used with audio recordings. VITC assigns a specific time in hours, minutes, and seconds to each vertical blanking interval in a video recording, along with a frame number. The time code can be used to start a recording at a certain chronological time (such as 5:00:00 p.m.), or it can be used to keep a playback machine synchronized with a master time source. The former application might be used by a home television viewer, while the latter application would more likely be used by a broadcaster.
MTC – MIDI Time Code - A form of time code representing real time in Hours: Minutes: Seconds: Frames: Subframes, and transmitted over MIDI. MTC can also be described as a way of sending SMPTE time code over MIDI cables. Like all forms of time code, MTC is designed to allow various pieces (in this case MIDI-equipped) of equipment to synchronize together.
14. Comment on MIDI Clock.
A MIDI timing reference signal used to synchronize pieces of equipment together. MIDI clock runs at a rate of 24 ppqn (pulses per quarter note). This means that the actual speed of the MIDI clock varies with the tempo of the clock generator (as contrasted with time code, which runs at a constant rate). MIDI clock does not carry any location information - the receiving device does not know what measure or beat it should be playing at any given time, just how fast it should be going.
15. Why is it desirable to synchronize two MIDI units via MIDI Clock?
MIDI clock allows the two units to run in sync and ensures no timing errors occur. One device acts as a master – the tempo/timing of the song and the position can be changed on the master and the slave will follow.
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
MIDI Clock - Principle role - to tell connected midi devices (sequencers / drum machines / sound modules) what the tempo is. Based on tempo and beats and bars – does not carry positioning information with the sync, therefore if it gets lost it stays lost.
Song Position Pointers - Principle role - to tell other midi devices where bar 1 is, where bar 2 is, etc. A high degree of accuracy (milliseconds) is needed for consistent control and lockup between video decks, audio machines and midi equipment running together.
Midi Time Code - MTC - Developed to give midi devices an absolute reference point, much finer than bars or beats. MTC is independent of musical tempo; it follows the same format as SMPTE – i.e. it carries positioning data continuously. This positional data is sent in short burst (four per frame). It takes 8 messages to complete the positioning data therefore the receiving MIDI device needs to read two frames before it gets the complete positioning information. The positioning information is updated every two frames.
(Midi machine control (MMC) - allows the sequencer to chase the audio recorder OR for the audio recorder to chase the sequencer - uses MTC to keep things locked up to a very tight degree of resolution).
17. Why is it desirable to synchronize a sequencer to multitrack tape?
A sequencer synchronised to a multitrack tape allows for MIDI sound modules to be recorded to separate track and still be synchronised and in tempo. A sound module with eight voices controlled by a sequencer and recorded to an eight track recorder synchronised to the sequencer will allow for up to 64 different sounds playing simultaneously:
8 sounds on each of the 7 tape tracks = 56 (one tape track will be the sync track).
8 sounds synced from the sequencer during mixdown = 64.
Therefore a sync multitrack tape gives more flexibility to even a simple MIDI setup. It allows synchronised MIDI sounds and overdubs to be recorded.
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
1 – Stripe a timecode to the tape – record 30 mins+ of timecode along the highest numbered track i.e. 8, 16, 24.
2 – Record each track from the sound module to the multitrack. When the tape is full more can be sequencer to sound during mixdown.
19. What is an audio sequencer?
Audio Sequencer – Software which allows audio to be recorded, edited, sequencer and mixed into a finished track. Usually such software also comes equipped with a MIDI sequencer, e.g. Cubase, Logic.
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analog or digital)?
Yes, audio sequencing software coupled with complimentary hardware (duplex / multi I/O soundcard, mixer) is a suitable replacement for a multitrack tape recorder. However some people prefer to keep their recordings in the analog domain and still prefer multitrack tape.
21. Comment on the suitability of an audio sequencer for sample and loop editing?
Sequencers are very well suited for sample looping, it is easy to visualise the loops, it is easy to cut, paste and edit the loop or individual loops, and it is easy to change eq and effects settings.
22. Why is it not straightforward to synchronize an audio sequencer to multitrack tape?
Timecode needs to be present on the tape before you can synchronize. This is not a straightforward procedure because when striping timecode onto the multitrack tape the level needs to be around 7 dB to 5 dB below 0, however many timecode generators have no output level control.
Two options are temporarily going through the mixer (ensuring no cross talk is recorded and that no EQ or effects are applied to the channel) then disconnect the generator, or buy a generator with an output level control.
Also 2 bars need to be left empty at the beginning of the sequence - 1 to make sure the sequencer catches up and syncs with the recorder, and 1 bar for a 4 beat metronome count in.
23. What parameters of effects can often be controlled via MIDI?
Effect amount, pan, mod, aftertouch, cut off, pitch, resonance, volume, volume of MIX out and LFO.
24. Why would you want to control effects parameters by MIDI?
MIDI can be used to automate effects as they are needed during the duration of a track. For example reverb can be programmed to effect drums in a certain section, or the reverb can be programmed to pan from left to right in tempo with the track for a special effect.
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
MTC comes in all four frame rates: - 30 fps, - 29.97 fps (30 fps drop frame), - 25 fps and - 24 fps
26. Does MTC contain an address?
No
27. Does MTC contain a clock?
MTC carries timing information in hours, minutes, seconds, and, frames.
28. Is MTC useful for synchronizing a MIDI sequencer?
Yes.
29. Is MTC useful for synchronizing digital audio?
Yes.
30. Is MTC useful for synchronizing analogue audio?
No.
31. Comment on the difference between standalone hard disk recorders and computer based hard disk recorders.
Hard disk recorders – Purpose built, good signal to noise ratios, can record on all tracks at once, dedicated hard drive, software and effects processors for audio recording, editing and mixing.
Computer based hard disk - general purpose, not normally designed with digital audio in mind, additional hardware required to enable the recording multiple tracks. However computer based hard disk systems offer greater flexibility with recording software, Virtual Instruments and software plugins/effects.
32. Why is it a problem to use hard disks for long term storage?
Instability / risk of malfunction / data corruption.
33. Onto what media does backup/archival storage take place?
CD-ROM, DVD-R, Zip Drive, RAID system.
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
Audio can be cut, paste and copied without having to spice or dub tape to another track. Also any editing done is non-destructive.
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
Advantage – Flexibility and integration with third-party audio software. Laptops more portable than standalone hard disk recorders.
Disadvantages – Desktop systems are less portable. Not designed specifically for audio tasks. Need to be set up carefully for digital audio use.
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
Pro Tools may be synced to a multitrack tape to add MIDI, loops and even use the programme to record some of the audio and copy it to other locations in the song. It therefore makes editing a much easier procedure.
37. List the common digital multitrack tape formats and describe their characteristics.
DASH - Digital Audio Stationary Head - 24 Track - Uses inexpensive reel to reel tapes. The quality will not diminish over time. Two-way compatible with 48-track DASH machines; the same tape used to record the 24 tracks of digital audio on the 24-track machine can be used to record the remaining 24 tracks of audio on the 48-track DASH.
MDM - Modular Digital Multitrack - 8 tracks per unit but more tracks can be obtained by linking multiple machines together by using internal time code. There are two types of MDM’s: ADAT and DTRS.
ADAT - Alesis Digital Audio Tape - Uses Video tape as a medium, capable of 8 tracks. Tapes need to be formatted before use. More machines can be synced to provide more tracks. A 2-hour ADAT tape, which is S-VHS, can hold about 40 minutes of audio. ADAT machines work in 20-bit resolution.
DTRS - hi-8 8mm 2-hour tape can hold about 108 minutes of audio. Some models can reach 24-bit resolution. The DTRS machines are preferred for post-production work over ADAT machines because they locate faster.
HDR - Hard Disk Recording - Uses a computer hard drive to store audio data. The use of dedicated hardware raises the number of audio tracks that can be used. When a recording is finished the audio files can be written to a CD ROM for later use.
38. What is 'formatting'?
The process of wiping a digital medium and preparing it for use in a particular system.
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
Advantages - Low SNR, no quality loss when copying, bigger headroom before distortion, easier to edit.
Disadvantages - No ‘analogue warmth’, expensive.
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
Analogue recorder – Heads need to be aligned, cleaned and be demagnetized.
Digital recorder – Hard disk needs to be kept clean (no unnecessary data) and defragmented.
A Digital recorder is easier to maintain without expert help.
41. Who carries out routine maintenance?
Qualified technician.
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
The heads can be cleaned using denatured or 91% isopropyl alcohol on a cotton swab. The swab should be dipped in the alcohol and then wiped on the heads.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
Denatured alcohol is should be used with a cotton swab. Care must be taken not to let the alcohol get on parts other than the pinch roller.
44. What are the effects of neglecting cleaning?
Poor recording / playback quality, loss of top end frequencies and problems if you are having to go back to an old tape and put on overdubs - the new tracks will sound different. Cleaning before every session is recommended.
45. Why must an analogue machine be periodically demagnetised?
The head picks up magnetic particles which affect the recording quality of the machine and can lead to tapes being erased.
46. What happens if a machine is never demagnetised?
The tape could be erased as the machines magnetizer may malfunction.
47. What might happen if the demagnetised is operated incorrectly?
The tape head may become even more magnetised.
48. Why do analogue tape recorders need to be lined up?
To ensure machine is operating at its most efficient and to ensure tapes recorded on one machine can be accurately played back on any another machine.
49. Do digital recorders ever need to be lined up?
DASH machines need to be aligned every six months by a qualified specialist using a laptop.
50. Comment on the three elements of line up.
The azimuth / relative angle of the head to the tape needs to be lined up perpendicular in order to insure optimal frequency response. If they aren’t aligned properly the HF can suffer.
Adjusting the bias is done to find the optimal balance between distortion, noise and maximum output level.
The recording and playback levels are adjusted to standard levels. This is done for both LF and HF.
51. Explain the need for monitoring in sync.
To prevent a delay in the musician hearing the recorded tracks and playing their part. If the musician was to listen to normal playback, he would play slightly behind.
52. Why is the sync signal inferior to the playback signal?
It comes from the record head and not the playback head.
53. Why does this matter in track bouncing?
Because bouncing is carried out by the record head, otherwise the tracks that aren't being bounced will be out of sync.
54. Is it possible to edit 2" analogue tape?
Yes by cutting and splicing it. It would be easier to record it into a system such as Pro Tools, edit it, and then return it back to tape.
55. Is it possible to synchronise two 24-track recorders?
In theory yes, although it would need to be 2 identical machines
56. Why is it often considered better to use an integrated disk recording system rather than one that uses a personal computer as the user interface?
An integrated system is designed specifically for the job of digital audio, the parts have been selected specifically for the purpose and the system has been tested and modified to handle digital audio. Most PC’s purchased are general systems set up for internet / home entertainment use. As a result they have a lot of things going on in the background other than audio application which puts a strain on the hard drive and processor. A PC also requires additional hardware, and is often much less portable than an integrated disk recording system.
57. Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
Disk recorders are presented as being much more user friendly than multitrack recorders – they are faster, have better sound quality, internal effect, allow for easy editing, etc. However multitrack tape still appeals to many people who wish to get a certain analogue sound. Therefore both systems continue to be used in studios around the world.
58. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
24
59. How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
24 in and 24 out.
60. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
Only 2 tracks could be recorded to individual tracks simultaneously. Also all mixing, effect, and eq would have to take place within the recording system as it is limited to 2 outputs only.
61. What information is stored in the session file?
Project title, fader positions, automation, audio edits, effects settings such as EQ, Send/Return, the arrangement of all recorded audio, sample / bit rate.
62. Are session files usually transportable between different systems?
This is possible if the different systems are using the same software and are equipped with the same plugins. People with a desktop and laptop setup with the same software can utilize this, however most people will not have the exact same set-up as other people. With Pro Tools the compatibility is also dependant on the number of inputs and outputs two different systems have.
63. Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
SCSI - Small Computer Systems Interface - A high speed parallel interface for hard disks, CD-ROM, scanners - Can be daisy chained - Fast and reliable.
ATA - Slower and can have buffer problems where data is bottle necked during transfer causing a loss of data – Cheap.
Firewire - Very fast - Hot swappable data transfer interface.
64. What is 'fragmentation'?
The process of "reads, writes and deletes" to a magnetic disk causes all kinds of unused small and large spaces on the disk and files are chopped up into many parts. Reading those fragmented files takes a lot longer compared to reading a file that is in one contiguous chunk on disk. File fragmentation is like a slow disk disease and needs to be cleaned up regularly.
65. Comment on archiving to CD-ROM.
CD-ROM archiving is supposed to be a stable and reliable method as long the CD-ROM’s are taken care of and stored in a safe place. However recent research claims that over a period of time CD-ROM are susceptible to losing their data. Another downside is the small amount of space available on a CD-ROM (700 MB) – DVD-R’s can hold more data.
66. What are 'virtual tracks'?
Virtual tracks are stored on a hard disk and act as different ‘takes’ of a track. Although they cannot all be played back simultaneously they can be exchanged with the selected project tracks. |
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