AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 9 - MIDI and Recording |
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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?
_________________
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 Nov 01, 2004 10:55 am |
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Rico1210
Joined: 03 Aug 2004
Posts: 39
Location: Newcastle, UK |
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Hi,
here are my answers to MIDI and recording questions. Some of my answers on MTC are rubbish, i've had real trouble finding advanced information on it 
1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
The cartridge on a record player is where the stylus is mounted. The cartridge often has a removable stylus, for easy replacement. The stylus is what houses the needle, which sits in the groove of a record and transfers the sound. The pickup arm is the mechanism that allows the needle to follow the groove of the record from outwards in. It holds the cartridge at one end and is balanced at the other end, so not to place too much weight on the needle. Turntables are essentially recorder players that usually have a pitch adjust slider that ranges from -8 to +8. Some turntables have other features that may include quartz lock or reverse. A DJ mixer is a simple 2 channel mixer (sometimes more than 2) with a crossfader between the 2 channels. It lets the DJ cue the output of each turntable in their headphones and also allows a microphone to be attached. Professional mixers usually have gain control and EQ (Hi,Mid,Lo) control on each channel. Some professional mixers have EQ isolators in the form of 'kill' switches, and the option of attaching effect processors.
2. Why can't the output of the cartridge be connected directly to a mixing console?
The output of the cartridge cannot be directly connected to a mixing console because an EQ filter is applied to the input when cutting vinyl. This removes the bass at a rate of 6dB per octave. The pivot point is around 1khz. Above this point the gain is increased, below it is reduced. This makes the cutting of the vinyl more efficient. Therefore a reverse RIAA EQ curve and a pre-amp are needed to boost the signal when connecting to a mixing console. Also the output level is around 5 mV, much lower than line level around 0.775 V. The required input impedance for a cartridge input is 47 kiloohm. The input impedance of a mic input is around 2 kohm, which is too low for a cartridge.
3. Why is it convenient to DI a synthesizer?
Direct Input or Direct Injection is used to connect a synthesizer to a mixer to convert the output to a low-impedance balanced signal, and to reduce the output to a suitable millivolt range for feeding microphone input. This eliminates problems with interference and ‘hum’. It is convenient to DI a synthesizer rather than have the signal changed from digital to analog via a speaker, then from analog back to digital via a microphone to the mixer.
4. Comment on the stereo output of many synthesizers?
Many synthesizers have more than one stereo output. Infact a lot of synthesizers come with 8 assignable outputs.
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
It may be desirable to amplify and mic up a synthesizer to capture the ambience of a particular room instead of a clear untouched sound. It may also be desirable to add some natural distortion from an amplifier.
6. Comment on the use of loops in recording.
Loops are used extensively in the recording of, for instance dance music. Drums are usually the most likely instruments to be looped, as they tend to be very repetitive. Rather than have a long recording of a repetitive drum beat, a drum loop would be used that is triggered after the necessary number of bars. Rhythm and bass sections also tend to be looped in the recording of dance music.
7. Comment on tape loops.
Tape loops can be created by splicing analog tape at the desired loop point and fixing the tape together at a zero crossing point. It is not always necessary to actually create loops in this way. An audio loop can be created electronically by feeding part of the playback head’s output into the recording input. It is often said that analog tape, and the sonic characteristics of tape delay have a unique quality that is difficult to simulate with digital electronics
8. Comment on looping using a sampler and sequencer.
Loops can be triggered to play from the sampler by the sequencer. The sequencer will tell the sampler to play the desired sample loop from a certain bar. For instance, a four bar drum loop would be triggered at the start of bar one, and then again at the start of bar 5 and so on.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
The sample is looped using the sequencer to make sure there are no timing differences between sequencer tracks. If the sample was looped using the sampler, eventually it will fall out of time with the sequencer. Using the sequencer to trigger the loop eradicates any timing deficiencies.
10. Comment on the significance of synchronising the sequencer to multitrack tape.
If a sequencer is to be used with multitrack tape then it must be synchronised so that the equipment attached to the sequencer plays together with the multitrack. This is achieved by tape sync. Tape sync is an audio signal created by a MIDI device that is recorded onto one track of the multitrack tape in the form of tones, and then played back into the device. Pre-recorded tracks can then be played by the mutlitrack unit and be in sync with MIDI devices attached to the sequencer.
11. Comment on the suitability of audio sequencers for sample looping.
Sample looping in a sequencer is based on the accuracy of the sample in question. If the sample is 'perfect' in repect to timing, then there will be no problem looping in a sequencer. However the only part of the sound you can guarantee to be in sync is the beginning, therefore timing differences will probably occur. Triggering the sample loop using the sequencer and the sampler is the preferred option, as this will ensure the start points of the sample are always in sync.
12. What is timecode?
Timecode is a means of synchronising machines and providing a real-time positional reference on tapes in the audio post-production industry. It is used in video editing and the editing of digital recordings, and is used in hard-disk recording for compiling edit lists and for synchronisation.
13. Comment on LTC, VITC and MTC.
LTC (Longitudinal TimeCode) is a system created by the Society of Motion Picture and Television Engineers that is also known as SMPTE code. It is basically an encoded signal recorded onto the audio track of a tape that contains registered time information in hours, minutes, seconds and frames. MTC (MIDI TimeCode) is a means of synchronising MIDI-controlled equipment to a real time reference. MIDI TimeCode is a way of transferring longitudinal timecode (LTC) around a MIDI system. Longitudinal TimeCode is a different format to MIDI messaging, therefore the signal must be converted into a MIDI compatible format ie. Status byte followed by data bytes. VITC (Vertical Interval TimeCode) is a form of timecode that is used in video tape recorders. It is recorded in the vertical sync period of a video picture rather than on an audio track, so that it can be read in slow motion and pause modes.
14. Comment on MIDI Clock.
MIDI data transmits timing information as part of a MIDI message called MIDI Clock data. MIDI Clock data is a series of electronic timing markers that are transmitted through the MIDI lead with the other messages. MIDI Clock is a relative timing device, since it depends on musical time or tempo.
15. Why is it desirable to synchronise two MIDI units via MIDI Clock?
It is desirable to synchronise two MIDI units via MIDI Clock so that they play together in sync. One device will be the master that controls the messages sent to the other device (the slave). Messages will include start, stop, continue, and tempo change.
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
MIDI TimeCode (MTC) is used together with MIDI Clock data and Song Position Pointers (SPPs). MIDI Clock data syncs devices in terms of their tempo, whereas Song Position Pointers tell devices how far through they are in terms of bars. MIDI TimeCode records physical time in minutes and seconds, together with MIDI Clock and Song Position Pointers enables a song to be started from a random point. For instance, if a song is to be started 2minutes 30seconds from the start, MTC, MIDI Clock and SPPs combine to make sure all devices are at the correct position in relation to the time.
17. Why is it desirable to synchronise a sequencer to multitrack tape?
MIDI sequencers and multitrack tape recorders can be synchronized together to give more flexibility in recording. Adding a multitrack recorder to a MIDI sequencer setup increases the possibilities in terms of how many sounds that can be played at the same time. A synthesizer with eight voices, together with a sequencer gives a possible of eight sounds being played together. If an eight track recorder is added to the equation, this enables all eight voices to simultaneously sound on all seven available tape tracks (It is limited to 7 because of the sync track). This gives the possibility of 56 voices.
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
First stage would be to create and plan the piece of music with the desired equipment and the sequencer. When the outline of the composition is complete it will then be ready to be recorded to multitrack tape. To enable sync, the tape must first be striped with timecode. Then the individual sequencer tracks can be recorded individually to the multitrack tape.
19. What is an audio sequencer?
In the field of electronic music, a sequencer is a device that records and plays back a sequence of control information for an electronic musical instrument. A MIDI sequencer plays back MIDI events and MIDI control information at a specified number of beats per minute. A sequencer records everything that goes into making the sound but not the sound itself, the sound is created by the devices attached to the sequencer. Sequencers offer the ability to edit and loop tracks very easily.
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analog or digital)?
An audio sequencer does not actually record signals like a multitrack tape recorder does. An audio sequencer holds information for a number of different instruments and enables the synchronised playback of the equipment. The information in a sequencer will eventually need to be recorded to a multitrack format to enable it to be played on a different machine.
21. Comment on the suitability of an audio sequencer for sample and loop editing?
Audio sequencers are very useful when it comes to sample and loop editing. The graphical interface of a sequencer makes it very easy to edit samples and create loops. Also, the ability to undo previous actions can prove to be very useful.
22. Why is it not straightforward to synchronise an audio sequencer to multitrack tape?
The best way of synching a sequencer to tape is to use a sequencer which has inbuilt SMPTE/EBU timecode capability. If this is not the case, then a MIDI/timecode synchronizer which converses with a sequencer via MIDI sync pulses and position pointers can be used. It is never straightforward to synchronise an audio sequencer to multitrack tape, as once the timecode has been striped to tape the tempo must not change.
23. What parameters of effects can often be controlled via MIDI?
Effects that can be controlled via MIDI include modulation, pitch bend, volume, panning.
24. Why would you want to control effects parameters by MIDI?
MIDI controlled effects enable those effects to be changed in real time, whilst playing a section of the song.
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
MIDI TimeCode covers the frame rate of SMPTE/EBU timecode. SMPTE/EBU timecode uses a rate of 25 frames per second.
26. Does MTC contain an address?
MIDI TimeCode must contain a binary address
27. Does MTC contain a clock?
Yes MIDI TimeCode contains a clock that records time in hours, minutes, seconds and frames.
28. Is MTC useful for synchronising a MIDI sequencer?
MIDI TimeCode is useful for synchronising MIDI sequencers to multitrack tape recorders. If the is not compatible with the timecode, then a convertor will be required to change MTC into SMPTE/EBU.
29. Is MTC useful for synchronising digital audio?
MIDI TimeCode is useful for synchronising digital audio on multitrack tape machines.
30. Is MTC useful for synchronising analogue audio?
As above, MIDI TimeCode is useful for synchronising analog multitrack recorders.
31. Comment on the difference between standalone hard disk recorders and computer based hard disk recorders.
The difference between a standalone hard disk recorder and a computer based hard disk recorder is that a computer based hard disk recorder relies on the systems of a computer to ensure that it works correctly. A standalone hard disk recorder has no such limitiation, as it is a separate device that can be guaranteed by the manufacturer.
32. Why is it a problem to use hard disks for long-term storage?
It is not advisable to use a hard disk for long-term storage, as they are a mechanical medium that contains perishable parts. If a part of the hard disk e.g. the arm were to seize, then the data contained on the disk would be lost.
33. Onto what media does backup/archival storage take place?
Backup/archival storage is generally copied to a digital medium, as they are non-perishable. Such media could be Compact Disc or Digital Versatile Disc.
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
The advantages of standalone hard disk recorders for editing are that the tracks are recorded on to the hard disk instead of tape. This makes it a lot easier to edit, as the editing will take place in a virtual environment where mistakes can be undone at the touch of a button. Whereas tape is more complicated to edit as it means splicing and joining pieces of tape, which can be difficult to undo.
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
A standalone hard disk recorder has the advantage that 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. Standalone hard disk recorders can be expensive. PC systems have the advantage that they can be much cheaper because they use standard computer industry hardware and operating systems, but they have the disadvantage that if you come across a problem there could be a number of causes. It could be the audio software, the audio hardware, the computer itself, the disk drive, the operating system or the hard disk driver software.
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
Using Pro Tools as an accessory to multitrack tape has the advantages are that there is no rewind time, and editing is much more flexible. If mixing is done internally, then the entire project can be stored in the session file and recalled at any later date.
37. List the common digital multitrack tape formats and describe their characteristics.
DAT - Digital Audio Tape. DAT recorders offer a range of sampling rates that include professional rates of 44.1 and 48 kHz. When recording, a DAT machine lays the tracks diagonally across the width of the tape unlike analog tape which records the signal parallel to the tape edge
DASH - Digital Audio Stationery Head. DASH format offers open-reel stationery-head recording formatsfrom 2 tracks up to 48 tracks. It operates at sample rates of 44.1 and 48 kHz
ADAT - Alesis Digital Audio Tape. ADAT machines are very affordable and are popular in budget music recording studios. ADAT is an eight-track digital tape recorder that uses the S-VHS 1/2 inch tape format. This tape is similar in design to the tape used in consumer VCRs.
DTRS - Digital Tape Recording System. DTRS machines are used in broadcasting and post-production of films. They use 8mm tape
38. What is 'formatting'?
To format a hard disk or diskette is to set up the space divisions on the medium and initiate a space allocation table that will know exactly how to reach each bit of data that may be stored there later.
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
The main advantage of analog multitrack over digital multitrack is the fact that they are universal. You can take a tape anywhere and find a machine to play it on. Digital multitrack recording tapes come in many different formats, which doesn't make it easy to transfer to a studio with a different type of recorder. Digital multitrack includes Serial Copy Management System(SCMS) to prevent illegal copying of tapes. There is no such restriction on the copy of analogue tape. Although an analog recorder should be cleaned by the recording engineer in the normal course of studio activities, a digital machine should only be cleaned by an expert, or thousands of dollars worth of damage can be caused.
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
There is a difference between the maintenance of an analog recorder and a digital recorder. Firstly you can do a lot of maintenance on an analog machine. You can't do more than run a cleaning tape on a digital recorder. The second is that you have to do the maintenance, otherwise performance will suffer.
41. Who carries out routine maintenance?
Routine maintenance will be carried out by the recording engineer unless there are specific problems, then a specialist in analogue recorder cleaning will be called.
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
The heads and all metallic parts that the tape contacts are cleaned gently with a cotton bud dipped in isopropyl alcohol. Isopropyl alcohol is only one of a number of alcohol variants, and it has good cleaning properties.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
The pinch wheel is made of a rubbery plastic. In theory it shouldn't be cleaned with isopropyl alcohol, but it often is. You can buy special rubber cleaner from pro audio dealers but in fact you can use a mild abrasive household liquid cleaner.
44. What are the effects of neglecting cleaning?
If cleaning is neglected on an multitrack tape recorder, metal parts will collect a residual magnetism that will partially erase any tape that is played on the machine. If cleaning is not done periodically then performance of the machine will be affected, this will be evident on any recordings made on the machine.
45. Why must an analogue machine be periodically demagnetised?
After a while, the metal parts will collect a residual magnetism that will partially erase any tape that is played on the machine. A special demagnetizer is used for which proper training is necessary, otherwise the condition can be made even worse.
46. What happens if a machine is never demagnetised?
If an analogue machine is never demagnetised then its magnetism will be so great that it will completely erase any tape that is played on the machine.
47. What might happen if the demagnetised is operated incorrectly?
If the demagnetiser is operated incorrectly further damage may be done to the the relevant parts of the recorder. A special demagnetizer is used for which proper training is necessary.
48. Why do analogue tape recorders need to be lined up?
Line-up or alignment, has two functions. The first is to get the best out of the machine and the tape, the other is 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?
Digital recorders do need lining up. This is a job for a specialist service engineer and not a recording engineer.
50. Comment on the three elements of line up.
The three elements of line-up are: Azimuth, Bias Level and Playback level. Azimuth states that the heads need to be absolutely vertical with respect to the tape otherwise there will be cancellation at high frequencies. The other adjustments of the head - zenith, wrap and height are not so critical and therefore do not need to be checked so often. Bias level - optimizes distortion, maximum output level and noise. Playback level - the 1 kHz tone on a special calibration tape is played and the output aligned to the studio's electrical standard level. On a 24-track machine 168 separate adjustments are required in line-up.
51. Explain the need for monitoring in sync.
Monitoring in sync is essential to be able to listen to or monitor previously recorded tracks while performing an overdub. The problem is that there is a gap between the record head and the playback head. If the singer sings in time with the output from the playback head, the signal will be recorded on the tape a couple of centimeters away, therefore causing a delay. This is the reason the record head is used as a playback head. The record head output isn't of very good sound quality as it is optimized for recording, but is good enough for monitoring.
52. Why is the sync signal inferior to the playback signal?
The sync signal is inferior to the playback signal as it is taken from the record head, which is optimized for recording and not playback.
53. Why does this matter in track bouncing?
Track bouncing must be done in sync, therefore cannot be done from the playback head for the same reason that monitoring cannot. There will be a delay because of the gap between the record head and the playback head. Track bouncing must therefore be done from the record head as the bounced tracks would not be in sync with the other tracks. The slight loss of quality has to be tolerated in order for the tracks to be in sync.
54. Is it possible to edit 2" analogue tape?
It is possible to edit 2" analogue tape by splicing the tape and then sticking it back together at the desired point.
55. Is it possible to synchronise two 24-track recorders?
It is possible to synchronise two 24-track recorders. This is done in analogue tape editing, when a 'spin in' is required.
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?
It is often considered better to use an integrated disk recording system rather than a medium that uses a PC as the user interface. This is because the performance of an integrated system can be guaranteed by a manufacturer and if there is a problem, you go back to the manufacturer. In a PC based system if you encounter a problem, there could be a number of factors to consider. It could be the software, the hardware, the computer, the operating system, the hard disk, the list goes on.
57. Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
The nature of tape demands that each track be given its own area across the width of the tape. So a tape recorder always has a fixed number of tracks. There are no such constraints in disk recording. The number of tracks of which a system may be capable depends on how fast the disk can access data, and how fast the rest of the system can process it. The speed of the disk is the main limitation. There are question marks over the progress of a disk recording than a tape recording. Recording a live event on tape can be almost guaranteed that the recording will be made successfully. There is always a doubt with disk recording that the recording will suddenly stop for no reason, or that when the recording is stopped it will be found that the disk is blank. Editing on a disk recorder is made a lot easier by the nature of the recording and the interface, whereas multitrack tape editing requires splicing the tape and fixing back together.
58. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
If a tape recorder has 24 inputs and 24 outputs, it will have 24 tracks. Tape recorders always have an equal amount of in inputs, outputs and tracks.
59. How many inputs and outputs would a disk recorder need if it were to be a replacement for a 24-track tape recorder?
A disk recorder being used as a replacement for a 24-track tape recorder could have as little as 2 inputs and 2 outputs. Although this would mean that no outputs other than the main stereo output could be used, and only 2 tracks could be recorded at once. If the recorder is to be used with a normal mixing console it would need 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?
As above. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, it's limitations would be that it can only record 2 tracks at once and would not be able to take any outputs other than the main stereo output.
61. What information is stored in the session file?
The session file contains information including the project title, audio files used, any edits, track assignments and mix and plug-in data.
62. Are session files usually transportable between different systems?
Session files can be transported between different systems provided the systems are compatible. For instance, if a session file is recorded and edited on a system with 16 inputs and outputs and mixed with a particular set of plug-ins. It will be very difficult to recreate the session on a system with only 8 inputs and a different combination of plug-ins. Session files are highly incompatible between manufacturers. SCSI is a parallel interface, therefore is faster than Firewire. SCSI disks are attached to a computer via an external interface for convenience. ATA(IDE) is the most common disk interface, although expansion is limited as this is strictly an internal interface but some systems allow an ATA disk to be mounted in a removable cartridge. There is no such thing as a 'Firewire disk' as Firewire is a medium that transfers data, therefore a 'Firewire disk' is an ATA disk with a Firewire bridge. The advantage of Firewire is that it is hot-swappable(connected/disconnected without PC shutdown) unlike SCSI.
63. Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
SCSI is a parallel interface, therefore is faster than Firewire. SCSI disks are attached to a computer via an external interface for convenience. ATA(IDE) is the most common disk interface, although expansion is limited as this is strictly an internal interface but some systems allow an ATA disk to be mounted in a removable cartridge. There is no such thing as a 'Firewire disk' as Firewire is a medium that transfers data, therefore a 'Firewire disk' is an ATA disk with a Firewire bridge. The advantage of Firewire is that it is hot-swappable (connected/disconnected without PC shutdown) unlike SCSI.
64. What is 'fragmentation'?
Fragmentation is when a file is stored in several 'chunks' instead of all together. Files are split and saved into separate clusters on a disk.
65. Comment on archiving to CD-ROM.
Archiving to an optical medium like CD-ROM is considered to be one of the most stable methods of storing data. Unfortunately the space available for storage is only 700MB on a standard CD-ROM.
66. What are 'virtual tracks'?
A Virtual Track or V-Track represents a workspace that can be used to hold recordings. A recorder may have lots of v-tracks but only the number of actual tracks allowed by the recorder can be played back at once. This means that on an 8 track recorder, an engineer is not limited to only 8 tracks of recording, but only 8 tracks can be played back. Tracks can be moved to v-tracks to enable more recordings to be made.
67. What is meant by 'edit density'? What are the implications of high edit density?
When audio is recorded it is placed in a long continuos section of the disk. This makes it easy for the disk to read. When the audio is edited, the regions that are to be replayed are not continuous. This makes it more difficult for the disk to read, potentially enabling less tracks to be replayed simultaneously. 'Edit density' describes the number of regions, their length and proximity to each other. If the regions are shorter and more densely packed, this is said to be high edit density. The problem caused by high edit density is that fewer tracks can be played simultaneously.
68. Does the editing and trimming of regions delete audio data from the disk?
Editing and trimming of disk regions does not delete audio from the disk. Editing and trimming is used to separate useful audio from non-useful audio. The audio is silenced but not deleted, as it may be required later.
69. In editing, what is the difference between 'slip' and 'grid' modes?
In grid mode of editing a grid is defined to enable regions to be snapped to a grid position when they are moved. They can then be given a time stamp to enable them to be found if moved. In slip mode there are no fixed time relationships between tracks, therefore any region or track may be 'slipped' in relation to others.
70. When might it not be possible to create a crossfade?
It is not possible to create a crossfade if audio is not beyond the region boundaries of the disk. If the audio does not extend beyond the region boundaries or if there is insufficient audio extended for the duration of the crossfade, a crossfade cannot be created.
71. What is 'bouncing', in the context of mixing?
Bouncing is when a number of tracks are grouped together onto a smaller number of tracks. For instance, a drum kit may have been recorded separately onto 5 or 6 tracks. These tracks can be grouped together into smaller tracks, maybe 2 tracks. This enables more playback tracks to be available for other instruments, instead of taking up 5 or 6 tracks they now only take up 2. V-tracks of the original recordings can be kept in case it is later felt that individual changes are needed. These can again be grouped or 'bounced' down to the required number of tracks.
72. What is meant by 'latency'? What is the difference between DSP processing and host-based processing?
Latency can be defined as the time it takes a packet of data to get from one designated point to another. The time it takes the data to reach the designated point then return to the sender is considered to be the latency. In other words, latency is delay.
Host based processing uses a PC's processor to complete the calculations needed for using plug-ins such as reverb effects. The amount of plug-ins that can be used at any one time is limited by the power of the host based processor, although more can be added if the buffer is increased. DSP (Digital Signal Processing) uses specially designed DSP chips that use audio signals in a different structure to host based processors. They tend to be very expensive but improve latency problems dramatically. |
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Sun Nov 07, 2004 3:24 pm |
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seanm
Joined: 06 Sep 2004
Posts: 20
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| week 9 task |
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sorry for delay chris
1. Describe the following equipment used by a DJ: Cartridge and stylus, Pickup arm, Turntables, Mixer.
Cartridge and Stylus. Situated a the end of the tonearm (pick up arm) are the cartridge and stylus connected via the headshell. The cartridge is a electro-mechanical device converting the movement of the styli on the record into an electrical signal. There are two types of stylus (or needle), spherical and elliptical. Professional DJ’s use spherical styli because they have the highest skip resistance and a higher output. Elliptical styli are designed for home use where playback is the sole purpose. They have a lower tracking force (easier on the vinyl) and a “truer” playback sound. The stylus traces the signal inscribed in the grooves. The better the stylus traces the signal the more accurate the sound reproduction.
Pickup Arm. The function of the pickup arm is complex. It is the relative motion between the armature and stator portions of the generating system of the cartridge, which produces the signal. Reproduction of the signal can only be true if the movement from the groove modulation is transmitted by the stylus/cantilever not be the stator or cartridge body. Unless the pick up arm holds the cartridge still against even the smallest movement the signal will be modified in some way. This results in a loss of clarity, dynamic range and transient attack.
Turntables. These come in two varieties; Direct Drive and Belt drive. Most professional DJs use direct drive turntables as belt drive turntables use less torque because the motor is not connected directly to the platter which, results in poor playback performance over time due to loosening of the rubber belt.
Direct drive turntables use a drive mechanism, which is directly attached to the platter. This mechanism uses a system of gears designed to provide enough torque to the platter enabling it to play almost instantly and at a constant speed without drag. This ensures a long playback life and greater control for the DJ.
Mixer. DJ mixers are used to mix the output from decks and other audio playback equipment, voices, samplers, instruments and outboard effects. They need to be robust (heavy and sustained use of faders etc.) and portable.
2. Why cannot the output of the cartridge be connected directly to a mixing console?
The output signal from a cartridge requires level conversion, impedance matching and reverse RIAA filtering. All of which is not available in a mixing console.
3. Why is it convenient to DI a synthesizer?
If the desire is simply to record the output from the synthesiser and isolate it from any other sound sources whilst converting the signal to a balanced one. This approach will have the added benefit of isolating the signal path and reduce the potential for ground loop hum.
4. Comment on the stereo output of many synthesizers?
Many modern synthesisers provide stereo outputs, this is to reflect the stereo nature of the patches and effects available on them
5. Why might it be desirable to amplify and mic up a synthesizer, as you would an electric guitar?
It might be desirable if;
The desired sound includes that of the microphone(s)/amplifier/speaker configuration.
The desired sound includes the above and characteristics of the space in which it’s being recorded.
Some level of spill from other microphones might be desired to produce a “live” feel to the whole recording.
6. Comment on the use of loops in recording.
Loops of many kinds are used extensively in modern recording and writing. Sometimes whole parts of songs are made up exclusively of pre-existing loops.
During recording looping can provide a method of comping a performance some elements of a song.
7. Comment on tape loops.
Tape loops were the pre-cursors of sampled loops. Indeed tape looping has been around for many years and formed the basis of “musique concrete” (a mid 20th century movement). Tape loops are made up manually by recording a phrase or passage to tape, editing it carefully and playing it back repeatedly using a separate tape machine.
8. Comment on looping using a sampler and sequencer.
Looping in a sampler is a little more time consuming than in a sequencer. Samplers utilise small screens and multi-level programming, the programming of loops under these circumstances has been described as “painting the hallway through the letterbox.
Sequencers with graphical displays, linear representation along the timeline and easy cut and paste functions make looping quicker and easier. Editing and altering loops in a sequence is also a much simpler operation.
9. Why is the sample looped using the sequencer in preference to looping it in the sampler?
When triggering such a sample the only part, which you can guarantee is in synch is the beginning. Unless the loop length is matched exactly to the tempo of the sequencer the timing of the loop will drift over the duration of a song. If however you retrigger the loop every two bars instead of looping it in the sampler, as long as the first beat is quantised to the first beat of every other bar in the sequencer, any timing discrepancies in the loop will be rectified every two bars.
10. Comment on the significance of synchronizing the sequencer to multitrack tape.
Synchronising a sequencer to multitrack tape enables the multitrack tape to be used efficiently as it is not necessary to record the sequenced tracks to multitrack. This leaves more tracks available for overdubs or extra instruments on the multitrack and reduces the need for track bouncing.
11. Comment on the suitability of audio sequencers for sample looping.
Such loops are relatively small audio files which along with the intuitive editing facilities of audio sequencers make then very suitable for sample looping.
12. What is timecode?
Timecode is a type of non-audio signal that contains information about elapsed time on a film, video/audio tape or disk recording.
13. Comment on LTC, VITC and MTC.
LTC, Longitudinal time Code is a timing signal which is part of an audio tape recording and is recorded on a track running longitudinally. LTC is one of the timing codes adopted by the Society of Motion Picture Engineers (SMPTE) the other being VITC (see below). LTC assigns a specific time in hours, minutes, seconds and frames. LTC can therefore be used to keep a playback machine in sync with a master time source.
VITC, Vertical Interval timecode is a timing signal that is part of a video recording. It is recorded in the vertical blanking intervals between successive picture frames, hence the name. VITC assigns a specific time in hours, minutes and seconds and frames to each vertical blanking interval in a video recording and is used to synchronise a playback machine to a master sync source.
MTC, Midi Time Code is a digital conversion of SMPTE timecode allowing midi devices to lock up in real time. MTC doesn’t contain any start or stop commands or change with tempo. MTC provides an absolute (positional) timing reference in minutes and seconds and frames rather than music related timing (bars and beats).
14. Comment on MIDI Clock.
Midi Clock (a status byte) is sent 24 times every quarter note. Advanced sequencers will also subdivide each midi clock twenty times giving a resolution of 480 times per quarter note. Unlike LTC, VITC and MTC Midi clock responds to tempo changes. Midi clock is transmitted over the same cable as all midi messages.
15. Why is it desirable to synchronize two MIDI units via MIDI Clock?
When two more midi devices are synchronised together they must share a common timing reference. The midi clock acts like a metronome indicating where the beats and subdivisions of beats occur. When two or more midi devices are synchronised together there can only be one source of event clock in the system, as such one device must be the master with the other(s) being slaves.
16. How does MTC correspond to MIDI Clocks and Song Position Pointers?
Mid clock contains song position pointers whilst midi time code (being absolute elapsed time) does not. Song position pointer messages tell receiving midi devices how many sixteenths have elapsed since the start of the sequence enabling them too sync to the exact point in the sequence.
17. Why is it desirable to synchronize a sequencer to multitrack tape?
Synchronising the two makes more efficient use of both giving the opportunity to free up sequencer tracks by recording them to multitrack or save multitrack tracks for more instruments or bouncing. Synchronising both enables midi and audio tracks to run together in real time starting and stopping together and lining up at any point for overdubs, drop ins etc. Keeping the midi parts in the midi domain for as long as possible allows them to be edited more easily. Indeed if they stay in the midi domain until mixdown they can still be edited later for any remixing.
18. Comment on the two stages of building up a recording on multitrack tape with the aid of a sequencer.
First is necessary to record the sync code to a track on the multitrack and then set up the sequencer to sync to this timecode. Now both the sequencer and multitrack are synchronised it is possible to begin recording. Decisions can then be made about what is to remain on the sequencer and what is to be recorded to multitrack.
19. What is an audio sequencer?
An audio sequencer is a software programme run on computer which can record and playback both midi and audio tracks.
20. Is an audio sequencer suitable as a replacement for a multitrack tape recorder (analogue or digital)?
Yes, audio sequencers are improving constantly and many can run a great number of audio and midi tracks simultaneously. There is some debate about analogue v digital sound and their respective qualities, which will continue I’m sure.
21. Comment on the suitability of an audio sequencer for sample and loop editing?
Audio sequencers are very suitable for sample and loop editing offering built in audio editors for this purpose. Many audio sequencers are so intuitive to use most editing and looping functions can be undertaken in the arrange page itself. Most offer time stretching and pitch shifting plug-ins as standard facilitating the production of loops and samples. The copy cut and paste functions allow the user to move loops and samples around the timeline offering experimentation possibilities.
22. Why is it not straightforward to synchronize an audio sequencer to multitrack tape?
Audio sequencers contain their own specialised timing reference designed to keep the digital audio and midi in sync. This in built digital audio clock is extremely stable and will not respond to the slight variations in timing inherent in timecode from other devices. The only solution is an external master clock for all components in a system, this solution isn’t compatible with all multitrack tape machines.
23. What parameters of effects can often be controlled via MIDI?
As long as the effect in question can respond to midi controller messages any parameter of the effect can be controlled via midi.
24. Why would you want to control effects parameters by MIDI?
Controlling effect parameters via midi is a way of adding movement and interest to a performance. As controller information this can be “played” in real time, stored and edited later.
25. Does MTC come in all the frame rates of SMPTE/EBU timecode?
Yes MTC is a digital version of SMPTE.
26. Does MTC contain an address?
Yes expressed in hours, minutes, seconds and frames.
27. Does MTC contain a clock?
No, MTC works with absolute time and transmits no tempo pulses.
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 multitrack hard disk recorders are dedicated hardware systems specifically designed for this purpose. They mimic the basic transport, operational and remote controls of a traditional multitrack recorder. These systems are attractive to some (particularly those accustomed to tape based systems) as they offer simple, dedicated multitrack controls, while offering the speed and flexibility of random access audio.
Computer based hard disk recorders are software programmes run on computers not specifically designed for this purpose (with the exception of the newer bespoke audio PC’s offered by companies such as Red Submarine and Millennium Music). These software packages differ in their features and operation and require the user to learn their idiosyncrasies. The computers on which these programmes run are usually not solely dedicated to this function. The capabilities of these systems are dictated by the hardware capacities of the system.
32. Why is it a problem to use hard disks for long term storage?
Hard disks contain moving parts, which can break down. They depend on other parts of a system to function (OS etc.). Data on hard disks can become corrupted making it impossible to retrieve the data stored on them.
33. Onto what media does backup/archival storage take place?
A large capacity high speed tape drive.
34. What are the advantages of standalone hard disk recorders (compared to tape) for editing?
Editing in standalone hard disk recorders is non-destructive.
Editing is also performed graphically enabling the operator to see the waveform being edited in great detail often down to individual sample level.
Once edits have been undertaken they can be copied and pasted to any position.
35. What are the advantages and disadvantages of computer based hard disk recorders compared to standalone hard disk recorders?
Advantages
Computer based hard disk recorders are relatively cheap compared to standalone hard disk recorders.
They offer an integrated package including audio and midi recording, editing, processing, mixing and mastering.
They are relatively portable.
They are regularly upgraded.
Their capacity is only limited by the hardware capacity of the host computer.
Disadvantages.
Computer based hard disk recorders vary in their designs and functionality.
They only allow one manual operation at a time.
Many people do not like operating mixers, effects etc. with a mouse or graphics tablet, preferring to get their hands on knobs and sliders.
They can cause RSI.
36. Comment on the use of Pro Tools as an accessory to multitrack tape.
Pro Tools is often used as an supplementary tool alongside another multitrack, such as a two-inch tape machine, digital multitrack tape or Otari RADAR, for example. In this situation, the contents of the multitrack can be transferred to Pro Tools to edit drums, tune and comp vocals, make song structure changes, and also serve as a backup.
37. List the common digital multitrack tape formats and describe their characteristics.
DASH, (Digital Audio Stationary Head) systems use a ½ inch open reel offer 24 and 48 tracks (cross compatible) support sampling frequencies of 44.1, 48 and 44.056kHZ and up to 24bit sample rate. DASH tapes can be spliced due to the interleaving of even and odd words. Also as error correction encoding and decoding is done independently on each track, any dropouts can be rectified without affecting other tracks and cross fading, punch in/out and electronic editing functions are all available.
ADAT types 1 and 2 can record and re-play 8 tracks of 16/20bit digital audio at 44.1kHz sampling frequencies and use S VHS video tape. Due to their modular nature ADAT machines can be linked together to record more tracks. Maximum record time 60 minutes
DTRS (Digital Tape Recording System) records and playback 8 tracks of 16/24bit audio at 44.1/48kHZ and uses a Hi8 cassette. Maximum record 108 minutes
38. What is 'formatting'?
Formatting in the context of digital tape refers to the preparation of tape prior to recording. Data is recorded on digital tape in a pre-defined pattern sometimes known as a “footprint”. Formatting creates the footprint onto which data can be written.
39. What are the advantages and disadvantages of digital multitrack compared to analogue multitrack?
Advantages
Longer recording times.
No tape hiss.
Non-destructive editing.
Virtual tracks
Bouncing in the digital domain.
Copies/backups with no degradation of sound quality.
Random access.
Reduced wear and tear on machines
Disadvantages
Sound quality of digital is not necessarily better.
Rapidly evolving technology leaves no time to really get under the skin of one system before it is changed.
Digital recording necessarily discards original source material that falls between samples.
Sampling leads to inaccurate representation of higher frequencies.
Tape saturation and compression heavily used in analogue recordings has to be emulated.
Digital recording involves latency.
40. Compare the maintenance and cleaning of an analogue recorder to that of a digital recorder?
Although an analogue recorder can be, and should be, cleaned by the recording engineer in the normal course of studio activities, a DASH machine should only be cleaned by an expert, or thousands of dollars worth of damage can be caused. The heads can be cleaned with a special chamois-leather cleaning tool, wiping in a horizontal motion only. Cotton buds, as used for analogue records will clog a DASH head with their fibre’s. Likewise, an analogue record can be aligned by a knowledgeable engineer, but alignment of a DASH machine is something that is done every six months or so by a suitably qualified engineer carrying a portable PC and a special test jig in his tool box. The PC runs special service software which can interrogate just about every aspect of the DASH machine checking head hours, error rates, remote ports, sampler card etc etc. With the aid of its human assistant it can even align the heads and tape tension.
41. Who carries out routine maintenance?
A knowledgeable engineer can carry out all routine maintenance on an analogue tape machine.
42. Describe how the heads and guides of an analogue machine are cleaned. Mention the materials used.
Heads and guides are cleaned using cotton swabs, (“Q Tips”) preferably the wooden kind and isopropyl alcohol (contains much less water). Dip the swab in the alcohol, wring it out against the side of the bottle so it is only damp, not dripping. Rub the heads and tape guides. Discard this swab and use a fresh one every time (dirty swabs should never be dipped back in the alcohol). Continue until the swab is clean after being rubbed against the heads and guides.
43. Describe how the pinch roller of an analogue machine is cleaned. Mention the materials used.
After cleaning the heads and guides engage the tape mechanism and using the same materials and procedure, clean the pinch roller. Some insist that pinch rollers (made of rubber) should not be cleaned with isopropyl alcohol as this will erode the rubber and suggest a small amount of household detergent.
44. What are the effects of neglecting cleaning?
If not cleaned a tape machine will not give the best quality in recording and playback. A build up foreign matter will clog the heads resulting in a “muddy” sound quality (no pun intended). Dirty heads will cause a loss of high frequency response and/or volume in recording and playback and an increase in “wow” and “flutter”.
45. Why must an analogue machine be periodically demagnetised?
Even thought they are made from materials with very low remanence tape heads can become magnetized. This magnetization causes high second harmonic distortion, clicks and tape splices. It can also produce low frequency noise (rumbling and popping) and high frequency noise (hiss). Magnetization can also partially erase recorded signals (especially those with short wavelengths).
46. What happens if a machine is never demagnetised?
See above
47. What might happen if the demagnetised is operated incorrectly?
It will magnetize the heads.
48. Why do analogue tape recorders need to be lined up?
The alignment of the three tape heads, erase, record and playback is crucial to the performance of an analogue tape machine. Poorly aligned heads result in a number of problems including “skewing”, dropouts and crosstalk.
49. Do digital recorders ever need to be lined up?
No
50. Comment on the three elements of line up.
The erase, record and playback heads often have five adjustments: height, azimuth, zenith, wrap and rack. The physical alignment of each tape head is an important factor in an analogue recorder’s performance.
Height determines the track’s vertical position in relation to the tape path. If a track is recorded and reproduced on heads that have different height settings, not all of the recorded signal will be reproduced, resulting in a compromised signal to noise ratio and increased crosstalk between multitrack channels.
Azimuth refers to the head’s tilt in the plane parallel to the tape. The head gap should be perpendicular (90 degrees) to the tape, this ensures that all track gaps are electrically in phase.
Zenith refers to the head’s tilt toward or away from the tape. Zenith must be adjusted so that the tape contacts the top and bottom of the tape with the same degree of force, otherwise the tape will tend to “skew” off it’s path. Skewing occurs when the tape rides up, down and even out of the guide path.
Wrap refers to the angle at which the tape bends around the head. It also determines the degree of tape to head contact and thus controls the heads sensitivity to dropouts.
Rack determines the pressure of the tape against the head. The forward the head is, the greater the pressure.
51. Explain the need for monitoring in sync.
Monitoring in sync is required as recording one or more tracks whilst monitoring previously recorded tracks via their respective play heads would result in a delay. In sync mode the monitor tracks are played from their respective record heads.
52. Why is the sync signal inferior to the playback signal?
On older machines sync mode produced a degraded replay signal because the record heads had wider gaps than the play heads causing less frequency resolution and the design of the head was different. Additionally in sync mode the record heads were simply switched to the standard replay electronics so no special equalisation was provided. In newer models however there is only a small difference in quality between the sync and standard play signals. With separate sync level and EQ provided any signal difference is minimal.
53. Why does this matter in track bouncing?
When track(s) bouncing previously recorded tracks are to played back and recorded to a new track(s) simultaneously. If the new track(s) are to be synchronised with the rest of the tracks this must be done in sync mode.
54. Is it possible to edit 2" analogue tape?
Yes
55. Is it possible to synchronise two 24-track recorders?
Yes this is achieved by interlocking the transport speeds of two or more machines using SMPTE. |
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Tue Nov 09, 2004 6:10 pm |
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