AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 7 - Disk editing systems and their operation |
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Lots to do this week Instinct, some repetition and some forward planning here also. Good luck.
1. Was DAT originally intended as a professional or a domestic recording medium?
2. What is the sampling rate of standard DAT?
3. What is the resolution of standard DAT?
4. What is 'azimuth recording'?
5. Describe the head wheel in DAT recorder.
6. What is SCMS?
7. What is the distinguishing feature of a DAT machine capable of near-simultaneous off-tape monitoring?
8. What is the sub-code area of the DAT tape used for?
9. What is 'interleaving'?
10. What is the width of the tape used for 24-track DASH?
11. What is the width of the tape used for 48-track DASH?
12. Describe how 24-track and 48-track DASH machines are compatible.
13. How are DASH tapes edited?
14. In DASH, why does a playback head come before the record head in the tape path?
15. Comment on the cleaning requirements of DASH How many tracks does a modular digital multitrack (MDM) have?
16. How can more tracks be obtained?
17. Comment on the types of usage of ADAT and DTRS machines?
18. Why is perceptual coding necessary?
19. Describe briefly the use of perceptual coding in the following:
Internet audio
Film sound
DVD-Video
Digital television
Personal stereo
20. What can be done, other than perceptual coding, to reduce bitrate?
21. What is masking?
22. How do perceptual coding systems handle signals that are probably going to be masked by other audio?
23. What is Huffman coding?
24. What is the typical bitrate for an MP3 file intended for Internet distribution?
25. What is the bitrate of Dolby AC3 as used in film sound?
26. What is metadata?
27. Describe and explain the following disk editing systems concepts and their operation:
• Comparison with analogue and digital tape editing
• Features, functions and parameters of disk editing systems
• Compatibility between systems of different manufacturers, and between earlier and later versions of the same system
• Operational procedures
• Automation and recall
• Plug-ins
28. What was the original purpose of timecode?
29. Briefly describe a synchronized system, using the words 'master', 'slave' and 'chase' in your answer.
30. Why is the reliable synchronization of audio not possible using MTC (MIDI timecode)?
31. If the speed of a digital recorder is varied due to being controlled by a synchronizer, what must happen to the sampling rate of the output? Give two answers.
32. From where does a digital recorder derive its clock in a synchronized system? Give two answers.
33. Briefly describe the synchronization of multiple ADAT machines (or DTRS).
34. In a synchronized system consisting of a sequencer and a drum machine, where the drum machine is the slave, what setting needs to be made on the drum machine to allow it to synchronize to the sequencer?
35. Before the introduction of song position pointers, what was likely to happen if the master was started at some point other than the start of the sequence?
36. What information do song position pointers provide?
37. Briefly, what is 'LTC'?
38. What is 'latency'?
39. What is 'zero latency monitoring'?
40. What is the drawback to zero latency monitoring?
41. What is DSP?
42. What is the advantage of using a system with DSP?
43. Describe the relationship between the number of plug-ins in use and the available processing power of the computer?
44. In relation to plug-ins, what is an 'instance'?
45. What is an 'insert effect'?
46. What is a 'bus effect'?
47. What problem might be caused by the latency of a plug-in?
48. What is an 'interleaved' sound file?
49. What is 'bouncing'?
_________________
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 Oct 18, 2004 6:11 am |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
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This is what I got for now.. I'll try to get the remaining questions answered tomorrow..
Week 7 – Disk Editing Systems And Their Operations
1. Was DAT originally intended as a professional or a domestic recording medium?
DAT was introduced in 1987. Even though it was intended to be the replacement for cassette players, it stayed as a professional recording medium due to its high price.
2. What is the sampling rate of standard DAT?
Standard DAT samples at a rate of 48KHz.
3. What is the resolution of standard DAT?
The resolution of standard DAT is 16 bit.
4. What is 'azimuth recording'?
In a DAT machine, the azimuth refers to the angle between the tape head gap, where recording takes place, and the tape track itself. A DAT machine uses two tape heads and they are angled at –20 degrees and 20 degrees. With these two heads, adjacent tracks can be recorded very closely and the edge of the preceding track can be overwritten to increase density. This is called azimuth recording.
5. Describe the head wheel in DAT recorder.
The head wheel spins at 2000 rpm’s and is 30mm in diameter.
6. What is SCMS?
SCMS stands for Serial Copy Management System and determines whether or not you will be able to make copies of the DAT tape. This is done using a 2 bit code named ID6 and a byte called ‘category code’ which identifies the source of a digital input.
7. What is the distinguishing feature of a DAT machine capable of near-simultaneous off-tape monitoring?
Adding an extra pair of heads allows the DAT to act like a three-head analogue tape recorder allowing simultaneous monitoring during recording.
8. What is the sub-code area of the DAT tape used for?
The sub-code area is used for time code and MIDI Machine Control data and insures that the DAT tape will be compatible with other DAT machines.
9. What is 'interleaving'?
Interleaving is an extra precaution against data dropouts during recording on a DAT. It works by scattering data so there is always enough to reconstruct the signal in case of a dropout.
10. What is the width of the tape used for 24-track DASH?
½ inch tape
11. What is the width of the tape used for 48-track DASH?
½ inch tape
12. Describe how 24-track and 48-track DASH machines are compatible.
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.
13. How are DASH tapes edited?
DASH tapes are edited by copying a segment of the audio to a second machine, which is then punched in at the desired position on the original machine. This is a similar process to the way videotapes are edited. DASH tapes can also be razor blade edited. This means that the tape can physically cut and pasted just like analogue tape.
14. In DASH, why does a playback head come before the record head in the tape path?
If the playback head didn’t come before the record head, synchronous overdubbing would not be possible due to the delay when the heads process the recorded and playback audio signals.
15. Comment on the cleaning requirements of DASH
The heads in a DASH machine can be cleaned with a special chamois-leather cleaning tool, wiping in a horizontal motion only. This should be only be done by a skilled expert. A qualified engineer should align the machine every 6 months using a PC that has service software that can check every aspect of the DASH machine.
How many tracks does a modular digital multitrack (MDM) have?
8
16. How can more tracks be obtained?
More tracks can be obtained by linking multiple machines together by using their internal time code.
17. Comment on the types of usage of ADAT and DTRS machines?
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.
18. Why is perceptual coding necessary?
Perceptual coding is necessary to reduce data, which can be done by removing material in the audio that is not audible due to auditory masking.
19. Describe briefly the use of perceptual coding in the following:
Internet audio
Film sound
DVD-Video
Digital television
Personal stereo
20. What can be done, other than perceptual coding, to reduce bitrate?
Predictive coding can also be used to reduce bitrate. It is a data reduction method, which has a ‘predictor’ that has knowledge of typical audio signal behaviour. The ‘predictor’ looks at the preceding audio signal and attempts to determine what will happen next and due to the repetitive nature of audio signals, the prediction is usually very accurate. The difference between the original signal and the prediction is then recorded as the data reduced signal. To regenerate the signal, a decoder must use the same ‘predictor’ knowledge and this is usually done to an accuracy of 98%. This accuracy is completely dependant on the predictor algorithm. To improve the precision of the system, a multi-band coding technique is also being used. This means splitting the signal into four frequency bands and applying separate predictors for each. One thing to be taken into consideration is that the encoder and decoder of the system must use the exact same predictor. Therefore, both have to be updated in order to ensure no signal degradation. The predictive coding system provides a 4:1 data reduction.
21. What is masking?
When the ear hears two tones with the same dominant frequencies, the louder tone will make the softer tone less sensitive to the ear and it will be masked so only the louder tone is audible. Lossy data compression methods, such as perceptual coding, take advantage of this phenomenon, since the human ear does not hear the masked tones anyways, they don’t need to be coded, therefore saving storage space.
22. How do perceptual coding systems handle signals that are probably going to be masked by other audio?
Using algorithms, the perceptual coding system determines the masked signal. Since the system knows that a masked signal won’t be audible to humans, it leaves it out of the coding to reduce the data.
23. What is Huffman coding?
Huffman coding is a method of coding introduced by David Huffman in a seminal paper in 1952. It works by varying the length of the encoded symbol in proportion to its information content. MP3 encoding takes advantage of this method.
24. What is the typical bit rate for an MP3 file intended for Internet distribution?
The typical bit rate is 128Kbs
25. What is the bitrate of Dolby AC3 as used in film sound?
In cinemas, Dolby AC3 uses a 640Kbs bitrate. On DVD’s and laserdiscs, the bitrate is 384Kbs.
26. What is metadata?
Metadata is data that comes with the audio. It holds information about the work such as authoring information (artist, label, engineer, year of release, genre etc.). Metadata can also be used to control certain characteristics of the audio. Metadata is documentation used for cataloguing the audio for preservation reasons.
27. Describe and explain the following disk editing systems concepts and their operation:
• Comparison with analogue and digital tape editing
Digital consoles, even the low-end ones are more ergonomically advanced than most analogue consoles. They have the advantages of automation, which is only found in the hi-end analogue consoles by way of computer automation. This is normally an inclusion in most digital mixing consoles in all price ranges. Digital consoles also have the benefit of scene memory where routing and effects settings can be stored for each mix and instantly recalled when needed. If the mixer also has a hard disk included, then it can function as a hard disk recorder as well. Since the audio can then be stored as non-linear data, editing can be done quicker and with visual aids..
• Features, functions and parameters of disk editing systems
Digital mixers include many features and functions. All included DSP effects and EQ’s usually come with libraries of presets for different instruments and inputs. Optional add-ons for a digital mixing console can include a meter bridge or extra input channels. Digital mixers also include a screen for visual navigation and menus for browsing through different internal routing and features. Using the screen, plugin effects can be edited and routed to selected channels. Disc recorders such as the Minidisc come with features such as track editing (renaming, moving, deleting), digital bass, playlist editing, functions such as repeating songs or entire discs. Many new models can also be connected to computers using USB and editing of parameters can be done through the PC.
• Compatibility between systems of different manufacturers, and between earlier and later versions of the same system
Since different systems may use different forms of data reduction or compression formats, transferring data between them may not be an option if one system doesn’t have the specific format of data reduction available. Then the system won’t be able to read the audio transferred. Session files and plugins from one system may not be compatible with another system and therefore the project data won’t function properly on the other system.
With earlier and later versions of the same system, there could be some problems if the different versions have different inputs and outputs, for example if you’re working on a Pro Tools HD 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 HD 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.
• Operational procedures
All instruments, samplers, external devices that need to be recorded should be connected to the mixer. If effects are required during recording, such as a compressor on vocals, then the effect should be routed as an insert to the microphone channel. The channel should also be routed to be output to the desired in of the recorder (PC with sequencing software). If no internal effects are desired then the input signal should be routed directly through the digital mixer and into the recorder at the highest possible bit rate available for optimal sound quality.
• Automation and recall
A major difference between analogue and digital mixing consoles is that with digital consoles you have the ability to save settings such as EQ, panning, effects, dynamics, fader levels and even routing settings into scenes. Different settings can be made and saved to separate scene memories and instantly recalled when needed. Since the digital mixing console can be used as a MIDI control surface, the automation can be recorded onto the external sequencer and stored there or on the console itself. This can then be edited and updated by navigating through the screen on the console.
• Plug-ins
Digital mixing consoles have DSP plugins that can be used to process the input signals. These include eq’s, compressors, reverbs and delays etc. Some may come included with the mixer but mid and hi end digital mixers usually come with expansion slots for further adding additional effects cards. The internal processing should at least be done at 24 bits as not to compromise the sound by truncation. This is why 32 bit internal processing is preferred for optimal sound quality.
28. What was the original purpose of timecode?
29. Briefly describe a synchronized system, using the words 'master', 'slave' and 'chase' in your answer.
A software sequencer and a drum machine are connected in sync. The software sequencer, Steinberg Nuendo for example, is the master. It sends out positioning and tempo information and start and stop commands to the drum machine, which is the slave. As the sequencer is triggered to play, it will send the play command to the drum machine and they will start in sync. Stop the sequencer and the drum machine will stop as well. If you start the sequencer in the middle of the song, the sequencer will send positioning information to the drum machine before it starts so the drum machine can ‘chase’ the sequencer, to catch up to the position in the song where the sequencer is starting.
30. Why is the reliable synchronization of audio not possible using MTC (MIDI timecode)?
31. If the speed of a digital recorder is varied due to being controlled by a synchronizer, what must happen to the sampling rate of the output? Give two answers.
32. From where does a digital recorder derive its clock in a synchronized system? Give two answers.
33. Briefly describe the synchronization of multiple ADAT machines (or DTRS).
34. In a synchronized system consisting of a sequencer and a drum machine, where the drum machine is the slave, what setting needs to be made on the drum machine to allow it to synchronize to the sequencer?
The drum machine needs to be set to be able to receive MIDI clock messages.
35. Before the introduction of song position pointers, what was likely to happen if the master was started at some point other than the start of the sequence?
All slaved equipment such as drum machines would not have any indication of where to start so would just start from the beginning.
36. What information do song position pointers provide?
SPP provide the song position in MIDI beats from the start of the song.
37. Briefly, what is 'LTC'?
Longitudinal Time Code 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.
38. What is 'latency'?
Latency is a delay caused by the components of a system. The latency time it takes an audio signal to be processed and move through the components of a system. The total latency is then the sum of all the smaller latencies caused by each component.
39. What is 'zero latency monitoring'?
This means that the input signal is routed directly to the output of the audio interface so the signal is heard instantly.
40. What is the drawback to zero latency monitoring?
Since the signal doesn’t go through the computer, no software-based effects processing can be heard on the signal.
41. What is DSP?
Digital Signal Processing is changing the characteristics of an audio signal digitally.
42. What is the advantage of using a system with DSP?
DSP chips are specifically designed for audio processing so the latency is always low. And if you are running a computer setup with an addition DSP card, then the plugins on the DSP card will not put a strain on the computer.
43. Describe the relationship between the number of plug-ins in use and the available processing power of the computer?
As the number of plugins being used increases, the CPU power decreases since the computer needs more power to process all the plugins.
44. In relation to plug-ins, what is an 'instance'?
An instance refers to the number of the same plugin being used. For example if you are using a Waves C4 multiband compressor on 4 separate channels, then four instances of the same C4 plugin are running.
45. What is an 'insert effect'?
This type of effect is inserted onto a track so the actual audio signal is affected. The types of effects that are used as inserts include equalizers, dynamics (compressors, limiters, expanders) and gates.
46. What is a 'bus effect'?
A bus effect or send/return effect doesn’t affect the actual signal but is combined with it. This effect has its own separate track and many audio tracks can utilize one bus effect. The audio tracks can then be bussed out to the effect at a desired level and that signal will blend with the original. Send/return effects include delays and reverbs.
47. What problem might be caused by the latency of a plug-in?
If it is an insert plugin, the track onto which it is inserted will play a little later than the other tracks and may have to be scrubbed back a little bit to make up for it. If the plugin is a send effect, i.e. a delay effect, then the set delay time won’t reflect the actual delay since the latency will be added to the time.
48. What is an 'interleaved' sound file?
This is a sound file where the left and right channels are joined to make one stereo file.
49. What is 'bouncing'?
It means taking selected audio tracks and mixing them down to one stereo or mono track. In the context of mixing, it means taking the entire mix and bouncing it to the hard disk as one stereo file (interleaved) or a left and right 2 file mix. This eliminates having to record the mix over to another medium when mixing down.
Last edited by iNSTiNCT2765 on Wed Oct 27, 2004 11:20 am; edited 1 time in total |
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Sun Oct 24, 2004 8:00 am |
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AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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You have done very well here, with some of these answers being excellent!
I understand time factors play a part here, but I do ask you to obtain the quality you are capable of in ALL your answers.
For example the difference between 26 and 27 is huge.
Try using examples as much as possible, you could have with the meta data question.
ok?
_________________
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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Tue Oct 26, 2004 8:06 am |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
yeah i'll try 
I got the rest of the answers coming and some I might need a little help on. I'll post them soon!
- Aman |
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Tue Oct 26, 2004 11:23 am |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
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Here's the rest of the questions, but some of them I need some help on..
19. Describe briefly the use of perceptual coding in the following:
Internet audio – MP3’s use perceptual coding for the low data rate and high quality output. Advances in the technology have introduced newer compression schemes such as the AAC (Advanced Audio Coding) used in the MPEG-4 codec, which introduces even higher quality output and a greater data reduction.
Film sound – Dolby AC-3 provides multichannel digital sound with perceptual coding. It provides high quality sound with remarkable data rate efficiency.
DVD-Video – DVD’s use the Dolby AC-3 perceptual coding method as well for high quality multichannel audio at a very efficient data reduction.
Digital television – ?
Personal stereo – ?
28. What was the original purpose of timecode?
30. Why is the reliable synchronization of audio not possible using MTC (MIDI timecode)?
This is because MTC is not as reliable as SMPTE. MTC doesn’t pass on positioning information as accurately as SMPTE.
31. If the speed of a digital recorder is varied due to being controlled by a synchronizer, what must happen to the sampling rate of the output? Give two answers.
The sampling rate must be changed accordingly to avoid a pitch shift in the output. (can’t find another answer).
32. From where does a digital recorder derive its clock in a synchronized system? Give two answers.
It can sync from SMPTE or MIDI.
33. Briefly describe the synchronization of multiple ADAT machines (or DTRS).
Multiple ADAT machines are synchronized by connecting the sync out connector of the first ADAT to the sync in connector of the next ADAT and so on. |
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Wed Oct 27, 2004 11:16 am |
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