AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 6 Equipment |
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1. 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?
Comment on the presentaNion of Nome disn recordnrs as rnplacements for nape mulnitrack necordern.
2. ff a tapn recordnr has 2n inputsnand 24 nutputs, how many tracks will it have?
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-tnack tapn recordnr?
3.nIf a dink recorning sysnem had nwo inpuns, two lutputs,land wasncapablenof twenny-four nracks, nhat would be its main limitations?
4. What information is stored in the session file?
5. Are session files usually transportable benween dinferent nystems?n
Comment briefny on thn suitabnlity ofnSCSI, AnA and Fnrewire nisks fon audio Necordinn.
6. nhat is 'fragmentation'?
7. Comment on archiving to CD-ROM.
8. What are 'virtual tracks'?
9. What is meant by 'edit density'? Whatnare thenimplicanions ofnhigh ednt densiny?
10f Does tNe editi,g and tnimming Lf regions deletn audio nata fron the diæk?
113 In edi9ing, wh8t is th4 differ8nce beteen 'sl p' and 4grid' m…des?
2. When might i not be2possibl2 to creÐte a cr6ssfade?
13. What is 'bouncing', in the context of mixing?
14. What is meant by 'latency'?
15. What is the difference between DSP rocessi:g and hst-base proces7ing?
ì6. Was 6AT orig€nally i4tended ‚s a pro9essiona' or a d mestic 8ecordin medium@
17. What is the sampling rate of standard DAT?
18. What is the resolution of standard DAT?
19. What is 'azimuth recording'?
208 Descri€e the h4ad whee9 in DATxrecorde0.
21.ƒWhat is4SCMS?
122. Des:ribe in‚what co8ditions3a DAT r corder 9ay be c‚pable of near-simultaneous off-tape recording?
23. What is the sub-code area of the DAT tape used for?
24. What is 'interleaving'? 6
25. Wh4t is th width 1f the t‚pe used3for 24-3rack DA H?
260 What iø the wi th of tXe tape 6sed for48-trac DASH? 9
27. Describe how 24-track and 48-track DASH machines are compatible.
28. How are DASH tapes edited?
29. In DASH, why does a playback head come before the record head in the tape path?
30. Comment on the cleaning requirements of DASH
31. How many tracks dnes a monular difital muntitrackn(MDM) hnve?
3n. How cnn more nracks bn obtainnd?
33n Commenn on thentypes of usage nf ADAT and DTRS machines?
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Mon Apr 12, 2004 5:11 am |
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solhamed
Joined: 04 Apr 2004
Posts: 5
Location: United Arab Emirates |
Can anyone recommend some sources for the first question?
I'm allright with the rest so far
Thanks,
S. |
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Wed Apr 14, 2004 12:15 am |
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hoggs33
Joined: 09 Feb 2004
Posts: 55
Location: Nottingham, England |
P.S I am struggling with question 22 - any ideas? |
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Wed Apr 14, 2004 6:42 pm |
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solhamed
Joined: 04 Apr 2004
Posts: 5
Location: United Arab Emirates |
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Duncan, thanks alot for the link...Gave me an excellent direction to head in..
And here are the answers i found:
1. 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?
Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
An integrated disk recording system as a "known quantity to the manufactue" inmplying that the manufaturer can gaurantee a certain level of performance. This also means that there is one vendor to assume responsibilty for any issues with the system.
Disk recorders are presented as replacements for tape multitrack recorders in an effort to ease transition i.e. Disk recorders are not inherently limited to the number of tracks they can record (this mostly dependent on the spped that hard disks can read data and the speed at which the data can be processed)
2. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
A tape recorder that has 24 inputs and 24 outputs will have 24 tracks. A disk recorder would need only one input and output to perfrom the same function.
3. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
It wouldn't be able to record more than two tracks at a time or take any outputs other than the main stereo output. For example it would not be possible to use an external reverb unit via an aux send and return.
4. What information is stored in the session file?
Project title
Audio files used
Edits
Track assignments
Mix and plug-in data
5. Are session files usually transportable between different systems? Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
Session files are not usually transportable between different systems.
SCSI:
Allows for external disks
Allows for several disks to use the same bus
Faster than ATA or Firewire
ATA (IDE or EIDE also) disks are :
cheap
not the fastest.
not designed to be external which means the expansion of storage capacity is limited (although some systems allow the ATA disk to be installed in a removable cartridge)
Firewire or IEEE 1394 (or iLink as Sony call it) is a fast serial interface, meaning that data travels along only one conductor in the Firewire cable. It is:
Faster than ATA disks
Self-configuring - no ID numbers to be set by the user.
Hot swap - devices can be connected and disconnected without powering down the system.
Bus power - the cable can transfer power from the host to the peripheral device, although this might not be sufficient for all devices.
Thin, flexible cable and robust connectors.
Target mode - where the internal disk of a computer can be connected to another computer as though it were just an external disk.
There is in fact no such thing as a Firewire disk. Firewire is simply a means of data transfer whereas ATA and SCSI intelligently determine the manner in which the data is allocated to the disk's platters. An external Firewire disk is therefore simply an ATA disk in an enclosure together with a 'Firewire bridge'.
6. What is 'fragmentation'?
Fragmentation is where the disk is unable to allocate contiguous disk space and occurs when the disk is nearly full or has been used over a long period of time without being completely erased
7. Comment on archiving to CD-ROM.
Archival to CD-Rom provides the best assurance of archival stability. Negatively, CD-Roms have a smaller storage capability regarding the actual size of data (<700 MB) and if an archival software is used than it will also be required to retreive the data.
8. What are 'virtual tracks'?
'virtual' tracks are tracks which are in synchronization with regular recorded tracks in a disk recording system, but that cannot be allocated to an output. Real tracks and virtual tracks can easily be exchanged. As systems become capable of replaying more and more tracks simultaneously, the relevance of virtual tracks will decrease
9. What is meant by 'edit density'? What are the implications of high edit density?
The term 'edit density' is used to mean the number of regions, their length and proximity to each other (shorter, more densely packed, regions make the disk work harder) and how far they are physically separated on the disk
10. Does the editing and trimming of regions delete audio data from the disk?
No, they are merely silenced.
11. In editing, what is the difference between 'slip' and 'grid' modes?
Slip: Since there is no fixed time relationship between tracks, any track or region can be 'slipped' with respect to the others. If it is known that a region (or whole track if no separate regions have been defined) is in the right place, usually it can be locked so that it can't be slipped accidentally.
Grid: It is usually possible to define a grid, so that regions will always 'snap' to grid positions when moved.
So the difference is that in the grid mode tracks will automatically snap to grid postions when moved and in slip mode tracks can be moved to any postion at all.
12. When might it not be possible to create a crossfade?
When audio from the outgoing region does not extend beyond the end of the region or Audio from the incoming region does not extend before the start of the region,
13. What is 'bouncing', in the context of mixing?
Bouncing can either mean mixing together similar tracks, such as backing vocals, and recording them onto fewer tracks to free up the original tracks for further recording or it can mean mixing the composition and recording it as a single track .
14. What is meant by 'latency'?
Latency is the delay that occurs between recording a signal and hearing that signal. It occurs in the sound card, in the software itself, and in the recording buffer.
15. What is the difference between DSP processing and host-based processing?
DSP (digital signal processing) are specially designed for processing audio signals. The latency of a DSP-based system is very low, of the order of 3 to 4 milliseconds.
16. Was DAT originally intended as a professional or a domestic recording medium?
As a domestic recorsing medium to supercede the compact cassette
17. What is the sampling rate of standard DAT?
48000 samples per second
18. What is the resolution of standard DAT?
16 bit.
19. What is 'azimuth recording'?
Azimuth recording funsction by eliminating the guard band betweenh tracks and positioning the angle of the playback head in such a way as to prevent it from being able to pick up signals from adjacent tracks. This results in a greater in a higher recording capacity
20. Describe the head wheel in DAT recorder.
The DAT recorder has a rotary head recorder that lays tracks DIAGONALLY across the width of the tape. This means that even though the tape speed is a only 8.15 millimetres/second, the actual writing speed is 3.133 metres/second.
21. What is SCMS?
Serial Copying Management System which was forced on the hardware developers by the software manufacturers (i.e. record companies) to prevent unlimited digital copying of CD's and other prerecorded media.
22. Describe in what conditions a DAT recorder may be capable of near-simultaneous off-tape recording?
The introduction and use of two more heads.
23. What is the sub-code area of the DAT tape used for?
Sub Code areas allow extra data to be recorded alongside the audio information like :
time codes which can log the total elapsed time and the time since the beginning of each item on the tape;
the Start ID marks the beginning of each item;
the Skip ID tells the machine to go directly to the next Start ID
24. What is 'interleaving'?
INTERLEAVING is a technique that scatters audio data across a media section so that if one section of data is lost, then there will be enough data elsewhere - hopefully beyond the site of media damage - which can be used to reconstruct the signal.
25. What is the width of the tape used for 24-track DASH?
1/2"
26. What is the width of the tape used for 48-track DASH?
1/2"
27. Describe how 24-track and 48-track DASH machines are compatible.
Tracks 25-48 are written into the spacing between the original 24 tracks therefor 24 track tapes can be played on 48-track DASH machines and the first 24 tracks of a 48-track tape will play on a 24-track machine.
28. How are DASH tapes edited?
29. In DASH, why does a playback head come before the record head in the tape path?
Due to the digital delay between reading data and playing it. iIf you analog overdubbing is to be performed where the sync playback signal comes from the record head itself there will be a slight delay while the playback signal is processed, and another delay while the record signal is processed and put onto tape
30. Comment on the cleaning requirements of DASH
The heads can be cleaned with a special chamois-leather cleaning tool, wiping in a horizontal motion only. Cotton buds, as used for analog records will clog a DASH head with their fibers. Likewise, an analog record can be aligned by a knowledgable 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
31. How many tracks does a modular digital multitrack (MDM) have?
8 tracks
32. How can more tracks be obtained?
Multiple machines need to be synchronized
33. Comment on the types of usage of ADAT and DTRS machines?
Maximum record time: ADAT - 60 minutes, DTRS - 108 minutes
ADAT popular in budget music recording studios
DTRS popular in broadcast and film post-production |
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Fri Apr 16, 2004 8:32 am |
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hoggs33
Joined: 09 Feb 2004
Posts: 55
Location: Nottingham, England |
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1 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
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.
2. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
24 – all tape recorders have the same number of inputs, tracks and outputs.
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
This depends a lot on the speed of the disk – the number of tracks a hard disk system might be capable of is not a constant. If the disk is fast enough, two inputs and two outputs could be enough for a 24 track system, but of course it would not be possible to record more than two tracks at once, nor take any outputs other than the main stereo output. A good compromise would be 8 inputs and 8 outputs to allow for recording several tracks at once and also to allow the use of outboard effects. However, this would still not be a complete replacement of a 24 track tape recorder to be used with a normal mixing console – to do this you will still really need 24 inputs and outputs.
3. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
- No separate outputs – you would only get the main stereo outputs therefore no foldback mixes etc.
- You would not be able to use a normal mixing console as the outputs would not be separated.
- Outboard effects could not be used.
4. What information is stored in the session file?
The project title, the audio files used, any edits, track assignments and mix and plug in data.
Typically each song would be given its own session file.
5. Are session files usually transportable between different systems?
Not always - for example if a session was recorded and edited on a system with 16 inputs and outputs and mixed in that system using a certain combination of plug in effects and you then tried to play that back on another similar system that only had 8 outputs and with a different combination of plug-ins, then it would take some effort to try and get the session sounding similar to the way it did originally. Session files are also highly incompatible between manufacturers.
Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
ATA is the most common disk interface because they 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.
SCSI is commonly regarded as an old interface on the verge of extinction. This is not so. SCSI does allow disks to be external to the computer, and disks can be daisy chained on a bus so that several can be connected at the same time. SCSI also has the advantage that being a parallel interface, data travels along several wires rather than a single data conductor of Firewire or USB and can therefore be faster than either.
Firewire is a fast serial interface, meaning that data travels along only one conductor in the Firewire cable. Firewire is fast, if not as fast as modern versions of SCSI, and has a number of features that SCSI lacks such as being self configuring, they are hot swappable, they have bus power and use thin, flexible and robust connectors.
There is in fact no such thing as a Firewire disk. Firewire is simply a means of data transfer whereas ATA and SCSI intelligently determine the manner in which the data is allocated to the disk's platters. An external Firewire disk is therefore simply an ATA disk in an enclosure together with a 'Firewire bridge'
6. What is 'fragmentation'?
This is when the disk is unable to allocate contiguous disk space and occurs when the disk is nearly full or has been used over a long period of time without being completely erased. Discontiguous recording forces the disk mechanism to w0rk harder and the system will be capable of fewer simultaneous tracks under this condition.
7. Comment on archiving to CD-ROM.
The main problem with archiving to CD-ROM is the relatively small amount of data a disk can hold (around 800mb). CD-ROMs however are very cheap. They can develop faults over time and long term storage may not be recommended on this medium.
8. What are 'virtual tracks'?
Unlike tape, digital recorders do not generally have a the same number of tracks, inputs and outputs. In addition, beyond the limit of the number of tracks that are re-playable simultaneously, many disk recorders can store additional virtual tracks which are in synchronization with the regular tracks, but cannot be allocated to an output. Real tracks and virtual tracks can easily be exchanged.
9. What is meant by 'edit density'? What are the implications of high edit density?
Edit density is used to mean the number of regions, their length and proximity to each other (shorter, more densly packed, regions make the disk work harder) and how they are physically separated on the disk. The greater the edit density the fewer tracks will play. If high density is causing a problem, two or more disks should be used so that tracks can be shared among them.
10. Does the editing and trimming of regions delete audio data from the disk?
No the edited or trimmed regions remain on the disk, but is silenced.
11. In editing, what is the difference between 'slip' and 'grid' modes?
In slip mode there is no fixed time relationship between tracks so any track or region can be ‘slipped’ with respect to the others. In grid mode it is usually possible to define a grid so that regions will always ‘snap’ to the grid positions when moved – the snap to grid can usually be set in a number of different ways such as whole notes, half notes, quarter notes etc.
12. When might it not be possible to create a crossfade?
To create a crossfade there needs to be audio on the disk that extends beyond the region boundaries. If there is no material beyond the region boundaries, or insufficient for the desired duration of the crossfade, then a crossfade cannot be creates.
13. What is 'bouncing', in the context of mixing?
Mixing together similar tracks, such as backing vocals onto a fewer number of tracks to free up the original tracks for further recording. This is what bouncing normally means in multitrack recording. However, in a disk system bouncing can also sometimes mean mixing. In this instance there is no need to record a mix to a separate medium, such as DAT, it can simply be bounced to disk as a stereo file.
14. What is meant by 'latency'?
Latency is the delay between performing an action (e.g playing a note on a keyboard) and it actually being heard.
15. What is the difference between DSP processing and host-based processing?
DSP is digital signal processing and is an alternative to host based processing which can sometime result in unacceptable levels of latency if too much is asked of the CPU. In DSP audio signals are different in structure from standard computer data and benefit from having DSP chips specially designed for the purpose. The latency of a DSP based system is very low (around 3 to 4 milliseconds), which for most purposes is unnoticeable.
16. Was DAT originally intended as a professional or a domestic recording medium?
Domestic but it never really took off with the public but was adopted by the ‘professionals’
17. What is the sampling rate of standard DAT?
16 bit, 44.1 or 48kHz
18. What is the resolution of standard DAT?
16 bit
19. What is 'azimuth recording'?
Azimuth is the angle of the tape head with respect to vertical. In digital recording to tape, the head can use azimuth to discriminate track recorded by a different head, and thereby increase recording density. This is because a track recorded with a cetain azimuth will only play back properly when reproduced using the same azimuth. A different azimuth used in playback will be attenuated.
20. Describe the head wheel in DAT recorder.
The head wheel in a DAT recorder is 30mm in diameter and spins at 2000 rpm. The tape is wrapped only a quarter of the way around, which means at times neither of the two heads is in contact with the tape. The tracks are laid diagonally across the width of the tape
21. What is SCMS?
Not sure if I’ve got the right thing here but the closest thing I can find is that SCMS is Serial Copy Management System which prevents illegal production of multiple generations of digital copies from a copyrighted original. Making a single copy for personal use by owners of digital audio home recorders is permitted.
22. Describe in what conditions a DAT recorder may be capable of near-simultaneous off-tape recording?
23. What is the sub-code area of the DAT tape used for?
The sub code area allows extra data to be recorded alongside the audio information. Data recorded can be as follows:-
A-time, which logs the time taken since the beginning of the tape
P-time, which logs the time taken since the last start ID
Start ID, which marks the beginning of each item
Skip ID, which tells the machine to go directly to the next start ID, thus performing and ‘instant edit’
End ID, which marks the end of the recording on the tape.
There is also a provision fro SMPTE/EBU timecode.
24. What is 'interleaving'?
This is a precautions against ‘drop outs’ in the audio playback. This scatters the data so that if one section of data is lost, then there will be enough data beyond the site of the damage which can be used to reconstruct the signal.
25. What is the width of the tape used for 24-track DASH?
½” tape
26. What is the width of the tape used for 48-track DASH?
Same as 24 track as far as I can gather as the 47 track DASH slots an additional 24 tracks in between the original 24 and therefore I assume uses the same width of tape .
27. Describe how 24-track and 48-track DASH machines are compatible.
If my assumption above is correct they will be compatible as they use the same width of tape. Therefore 24 tracks could be recorded on a 24 track machine and if extra tracks are needed then a 48 track machine could be brought in and the tape from the 24 track machine put into the 48 track machine to record up to another 24 tracks in the ‘guard bands’ left by the other machine. The machines however are two way compatible as well. So if it is decided that the extra tracks were not needed then the tape could be put back on the 24 track machine and still play back OK with no ‘interference’ from the extra tracks that were recorded.
28. How are DASH tapes edited?
DASH was designed to be a cut and splice editing format. However it was found in practice that edits were often unreliable. Editing of DASH tapes is now done by copying between two machines synchronized together with an offset.
29. In DASH, why does a playback head come before the record head in the tape path?
While analogue processors take place virtually instantaneously, digital operations take a little time. So if you were carrying out analogue overdubbing where the sync playback signal comes from the record head itself, this would not work in the digital domain as there would be a slight delay while the playback signal is processed and another delay while the record signal is processed and put onto tape (105 milliseconds to be precise!!!!). In order therefore to perform synchronous overdubs there has to be playback head ‘upstream’ of the record head otherwise the multitrack recording process will not work.
30. Comment on the cleaning requirements of DASH
A DASH machine should only be cleaned by an expert otherwise 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 fibres.
31. How many tracks does a modular digital multitrack (MDM) have?
8.
32. How can more tracks be obtained?
Multiple machines can be connected together and synchronized to give more tracks.
33. Comment on the types of usage of ADAT and DTRS machines?
ADAT is popular in budget music recording studios. DTRS is popular in broadcast and film post production. |
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Fri Apr 16, 2004 10:43 pm |
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iNSTiNCT2765
Joined: 05 Nov 2003
Posts: 60
Location: Denmark |
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Week 6 – Equipment 2 8O
1. 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?
Firstly, an integrated disk recording system is 100% dedicated to audio recording and editing and is designed specifically for that purpose. It is also more portable than a desktop PC or Mac used for the interface since an integrated disk recording system is usually contained within one piece of equipment.
Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
Disk recorders don’t have to be aligned as tape recorders do. Tape doesn’t have to be purchased for a disk recorder, as audio data is stored on a harddisk instead of analogue tape. Disk recorders are also cheaper than multitrack tape recorders.
2. 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.
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
It would need 24 inputs and 24 outputs for a disk recorder to act as a full replacement for a tape recorder.
3. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
The most obvious limitation here would be that the recorder would not be able to record any more than two mono tracks or one stereo track simultaneously. Tracks would have to be recorded two at a time if mono or one if stereo. With only two outs, there would be no option of routing individual tracks to their own channels on a mixing console since there only is a master mix out available. Everything would have to be mixed inside the disk recording system.
4. 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.
5. 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.
http://www.datolitemusic.com/prestdmb.html
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.
6. 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.
7. Comment on archiving to CD-ROM.
Archiving to CD-ROM is good due to its stability but a downside is the limited space per CD.
8. 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.
9. 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.
10. Does the editing and trimming of regions delete audio data from the disk?
Even if an audio track is trimmed or edited, the actual unprocessed audio file would usually still be stored in the audio pool.
11. In editing, what is the difference between 'slip' and 'grid' modes?
If grid mode is selected, moving an audio region back or forth will automatically snap it into place to the closest line in a defined grid. If the sequencer is in slip mode, the region will not snap into place but stay, as is, exactly where it has been moved.
12. 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.
13. 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.
14. What is meant by 'latency'?
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.
15. What is the difference between DSP processing and host-based processing?
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.
16. 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.
17. What is the sampling rate of standard DAT?
Standard DAT’s sample at a rate of 48 KHz.
18. What is the resolution of standard DAT?
Standard DAT’s have a 16 bit resolution. 24 bit DAT’s are available too.
19. 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.
20. Describe the head wheel in DAT recorder.
The head wheel spins at 2000 rpm’s.
21. 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.
22. Describe in what conditions a DAT recorder may be capable of near-simultaneous off-tape recording?
I found this explanation but it doesn’t make much sense to me.
“If an extra pair of heads is mounted on the drum [head wheel??], simultaneous off-tape monitoring can be performed during recording just like a three-head analogue tape recorder”
From http://www.music-recording.com/stereo_recording/dat.html
23. 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.
24. 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.
25. What is the width of the tape used for 24-track DASH?
A 24 track DASH (digital audio stationary head) uses ½” tape.
26. What is the width of the tape used for 48-track DASH?
The same width of tape is used with a 48 track DASH recorder.
27. 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.
28. 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.
29. 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.
30. 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.
31. How many tracks does a modular digital multitrack (MDM) have?
They each have 8 tracks.
32. How can more tracks be obtained?
More tracks can be obtained by linking multiple machines together by using their internal time code.
33. 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.
Last edited by iNSTiNCT2765 on Mon May 03, 2004 7:09 pm; edited 3 times in total |
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Fri Apr 16, 2004 11:34 pm |
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griff505
Joined: 23 Feb 2004
Posts: 68
Location: Bristol |
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1. 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 entire system has been set up by the manufacturer for the purpose of audio, therefore performance is guaranteed, and it is dedicated to audio tasks
- If any problems arise it is easy to go back to the manufacturer, or their website for a solution.
- An integrated system is easier to transport as it is one piece of hardware, and as a result is easier to transport and set up and live recording sessions.
Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
With tape each track needs its own area across the width of the tape, and therefore there are always a fixed number of tracks. With disk recording, data is recorded on the disk in three dimensions, not necessarily contiguously or in sequence. 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.
2. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
- 24
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
Technically two inputs and two outputs would be enough to create a 24 track mix on an integrated recoding system. However this would limit the amount of tracks that could be recorded simultaneously. Eight inputs and eight outputs is a compromise and suitable for many recording situations, however it is not a ‘complete’ replacement for 24 inputs and 24 outputs.
3. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
The number of simultaneous inputs and outputs:
- Only two tracks could be recorded to at any one time.
- Only one stereo would be possible, which would not allow for any foldback mixes, effect sends, or external mixing consoles to be used
4. What information is stored in the session file?
When a new project is started often a new hard disk will be inserted into the system, within the hard drive session files are created. Session files contain information on project title, audio files, edits, track assignments and mix and plug-in data. These are created for each track.
5. Are session files usually transportable between different systems?
Session files can be transferred between systems, however there are often complications. For example a recording and editing session may take place on an integrated disk system with 16 inputs and outputs, and mixed using a particular set of plug-ins. If this way later played back on an integrated disk system with only 8 inputs and outputs and a different set of plug-ins it would take time to get it back to the original sound. However usually it would be the other way round, i.e. at the later stage a system with more inputs and outputs would be used (for example, mixing a project in a pro-studio after the tracks were recorded at a home, or mobile studio setup).
A further problem is that session files are highly incompatible between manufacturers, a disk cannot simply be taken from one system and be expected o work on another.
Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
SCSI – This is often seen as an ‘old’ interface, on the verge of extinction, however SCSI has a number of advantages. It does allow for external disks to be connected to the host, which can be daisy chained allowing several to be connected at once. It is a parallel interface which means that data can travel along several wires simultaneously and is faster than Firewire.
ATA – The most common type of interface, also known as IDE or EIDE. They are cheap but not the fastest interface, and also do not lend themselves to external disk setups and so have limited storage expansion capabilities.
Firewire – This is a fast serial interface whereby data travels along one conductor in the Firewire cable. It is a fast connection, self-configuring, hot swappable, capable of bus-powering, and allows target mode (where the internal disk of one computer can be connected to another as though it were an external disk).
6. What is 'fragmentation'?
Fragmentation occurs naturally when you use a disk frequently, creating, deleting, and modifying files. At some point, the operating system needs to store parts of a file in noncontiguous clusters. Although entirely invisible to users, it can slow down the speed at which data is accessed because the disk drive must search through different parts of the disk to put together a single file. It can occur more frequently if the disk is nearly full or has been used over a long period of time without being completely erased. It is a reason why a drive dedicated to audio is recommended for integrated disk systems.
7. Comment on archiving to CD-ROM.
Archiving to CD-ROM is cheap and quick, however the durability and archival life of CD-ROM storage is still not proven. Also CD-ROMs can only hold a relatively small amount of data
8. What are 'virtual tracks'?
Added to the number of tracks that disk recorders can play simultaneously, they can also store virtual tracks in synchronisation with regular tracks. Although they cannot be allocated to an output they can easily be exchanged with regular tracks which make them ideal for storing various takes of any track.
9. What is meant by 'edit density'? What are the implications of high edit density?
Audio is recorded to long continuous sections on the disk which easy to retrieve. However once the data is edited and replayed the audio is no longer continuous on the disk. The heads on the disk have to work harder and move more often to retrieve the data. This has an effect on the number of tracks that can be simultaneously played-back by the machine. “Edit density” refers to 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 few tracks will play. The use to two disks can ease some of the problems created by edit density.
10. Does the editing and trimming of regions delete audio data from the disk?
The audio that is not referred to by a project is retained on the disk and is silenced.
11. In editing, what is the difference between 'slip' and 'grid' modes?
Slip – Unlike tape, an integrated disk recording system allows tracks to be moved forwards or backward in time in relation to each other. When a track is moved with respect to others it is ‘slipped’. When it is recorded it is given a time stamp and if moved can be ‘spotted’ back to the original’ position if needed.
Grid – In a grid mode regions will ‘snap’ to the grid positions when moved
12. When might it not be possible to create a crossfade?
A crossfade cannot be created if there is no material beyond the region boundaries or there is insufficient audio for the desired duration of the crossfade.
13. What is 'bouncing', in the context of mixing?
‘Bouncing” involves the mixing together of similar audio tracks onto fewer tracks to free up the original tracks for further recording or taking the entire mix and bouncing it to the hard disk as a mixed stereo file.
14. What is meant by 'latency'?
On an integrated disk recording system the buffer is the short amount of time during which the processor performs its calculations, and at other times allows the processor to catch up if it was struggling. The size of the buffer is critical when overdubbing as anything over 10ms is audible and distracting for the performer, it is this which is know as latency. It occurs in the sound card, the software and in the buffer.
15. What is the difference between DSP processing and host-based processing?
DSP or digital signal processing is beneficial as it is specially designed for the purpose of audio. DSP based systems have a very low latency, often below 3-4 ms, which is unnoticeable. DSP can work in combination with host-based processing and take the strain off the hosts processor.
16. Was DAT originally intended as a professional or a domestic recording medium?
DAT was originally intended as a domestic recording medium (failed due to high price).
17. What is the sampling rate of standard DAT?
48 KHz – to avoid the possibility for digital copying of machines (some professionally modified machines will operate at 44.1 KHz from analogue inputs).
18. What is the resolution of standard DAT?
16 bit (recent modifications allow the storing of up to 20 bit audio).
19. What is 'azimuth recording'?
Azimuth is the orientation of the head gap with respect to the tape. The gap should be exactly perpendicular to the edge of the tape otherwise the following occurs:
- High frequencies are not efficiently recorded or replayed because the head gap becomes wider as far as the tape is concerned.
- The relative phase between tracks is changed.
‘Azimuth recording’ takes advantage of azimuth error: Rotary-head tape formats have been developed with one or more pairs of rotating heads which have opposing or complementary azimuth angles, thereby enabling the recording of adjacent tracks very closely, or even overwriting the edge of the preceding track in order to increase density.
20. Describe the head wheel in DAT recorder.
The head wheel is 30mm in diameter and spins at 2000 rpm. Tracks are written diagonally across the tape which allows the data to be written and read at a faster rate than the actual tape speed.
21. What is SCMS?
Serial Copy Management System - Originally put in place through the insistence of the RIAA as an anti-piracy measure, it aimed to prevent unlimited cloning of DAT’s and CD’s. It effectively killed the use of DAT's at the consumer level.
22. Describe in what conditions a DAT recorder may be capable of near-simultaneous off-tape recording?
If an extra pair of heads is mounted to the DAT recorder simultaneous off-tape monitoring can be performed during recording just like a three-head analogue tape recorder.
23. What is the sub-code area of the DAT tape used for?
Sub-code allows extra data to be recorded alongside the audio information. For example:
- Start ID marks the beginning of each item.
- A-time, which logs the time taken since the beginning of the tape.
24. What is 'interleaving'?
Interleaving is a recording method that reduces data errors during playback. Instead of being written in a contiguous data stream, data sectors are intermixed along the recording track. If a DAT should have a smudge or scratch, the entire data file is generally recoverable because a smaller amount of the file data is affected.
25. What is the width of the tape used for 24-track DASH?
½”
(The DASH - digital audio stationary head - format uses reel-to-reel transports and stationary heads to record digital audio).
26. What is the width of the tape used for 48-track DASH?
½”
27. Describe how 24-track and 48-track DASH machines are compatible.
A project can be started on a 24-track machine and completed on a 48-track recorder if needed, as the data from tracks 25-48 are written into the spacing between the original 24 tracks. However, if the tape is the played back on the 24 track machine, only tracks 1-24 will be played.
28. How are DASH tapes edited?
DASH tapes can be physically cut and pasted like analog tape. To allow this, electronic circuitry is employed to conceal the damaged data block and buffer and crossfade the two ends of the edit. The sophistication of the DASH machines is reflected in their price.
29. In DASH, why does a playback head come before the record head in the tape path?
Because the digital heads cannot be made to record and play at the same time. The problems associated with overdubbing are addressed by using a second write head after the read head and using digital delay to synchronize the playback with the incoming audio
30. Comment on the cleaning requirements of DASH
DASH machines should only be cleaned by an expert who uses a special chamois leather cleaning tool moved only in a horizontal direction. Every 6 months the DASH should be aligned using specialist computer software.
31. How many tracks does a modular digital multitrack (MDM) have?
A Modular Digital Multitrack is an 8 track multitrack digital recorder than can be run in synchronization with other machines of the same type to attain more tracks. ADAT brand recorders are an example.
32. How can more tracks be obtained?
By synchronising multiple MDM’s.
33. Comment on the types of usage of ADAT and DTRS machines?
ADAT - Alesis Digital Audio Tape – Developed in the early 1990's the ADAT records eight tracks digitally on a standard 1/2" SVHS video cassette. ADAT is arguably the most significant technology / price breakthrough for recording studios in the last 20. The ADAT has gone through several generations and is currently a 20-bit digital format. The ADAT optical connections for transferring digital data 8-tracks at a time have become a standard of the industry and are used in a wide range of products from many manufacturers. A 2-hour ADAT tape (S-VHS) can hold about 40 minutes of audio.
DTRS - An 8-channel digital audiotape format which uses Hi-8 metal-particle cassettes. Some models are capable of 24-bit resolution. DTRS machines are preferred for post-production work over ADAT machines because they locate faster. |
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Tue Apr 20, 2004 10:21 pm |
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albertom
Joined: 21 Jan 2004
Posts: 22
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1. 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?
Comment on the presentation of some disk recorders as replacements for tape multitrack recorders.
Disk recorders come in two types, one is as a complete system, the other is as a software and peripherals to operate in conjunction with a standard personal computer. Complete systems have certain advantages:
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.
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 distinct disadvantage that if you come across a problem, who do you turn to for help?
2. If a tape recorder has 24 inputs and 24 outputs, how many tracks will it have?
How many inputs and outputs would a disk recorder need if it was to be a replacement for a 24-track tape recorder?
All tape recorders have the same number of inputs, tracks and outputs. So for example, a 24-track recorder always has 24 inputs, 24 tracks and 24 outputs. There wouldn't be any point in any other arrangement.
3. If a disk recording system had two inputs, two outputs, and was capable of twenty-four tracks, what would be its main limitations?
Once the number of tracks ceases to be a constant, the question of how many inputs and how many outputs is thrown wide open. The fewest could be two inputs and two outputs. If the disk is fast enough, this could be a 24-track system, or even more, but you wouldn't be able to record more than two tracks at once, nor take any outputs other than the main stereo output.
4. What information is stored in the session file?
With a conventional tape recorder, you would start a session by taking out a new reel of tape and loading it on the machine. There has to be an equivalent to this in disk recording.
With removable hard disk cartridges available, the process could be very similar. Take out a new hard disk and connect it to the system. But within this there is also the process of creating a new 'session file'. Manufacturers tend to have their own terminology, but it's reasonable to use Digidesign's terms since Pro Tools is so common. The session file contains a lot of information about the project:
Project title
Audio files used
Edits
Track assignments
Mix and plug-in data
Typically each new song would be given its own session file.
5. Are session files usually transportable between different systems?
Comment briefly on the suitability of SCSI, ATA and Firewire disks for audio recording.
One difference between the session file and a reel of tape is that the session is not so easily transportable. For instance, a session might be recorded and edited on a Pro Tools system with 16 inputs and outputs and mixed within Pro Tools using a certain combination of plug-in effects. If you try and play that back on another Pro Tools system with only 8 outputs, and with a different combination of plug-ins, then it will take some effort to get the session sounding similar to the way it did originally. With tape, you know that you can record on one machine and play back on another without any problems, assuming the machines are properly aligned, and you don't expect the tape to contain mix data, so it is a completely natural process simply to reconstruct a rough mix.
Also, session files are highly incompatible between manufacturers. There are moves towards compatibility, or at least common transfer processes, but you can't just take a disk recorded on one system and expect to get any sense out of it at all on another.
The choice of disk media isn't as tricky as it once was. There used to be the problem that hard disks need to recalibrate themselves every so often to account for the heating and expansion of the disk platters but the manufacturers have now mostly found workarounds to this. It is still necessary for a disk to achieve a certain level of performance, and the rotational speed of the platters should ideally be at least 7400 revolutions per minute, preferable 10,000 rpm. Most modern disks will be capable of simultaneous record and playback of at least 24 tracks. Note that the very small disks used in laptop computers may have a rotational speed of only 4800 rpm so either the track count will be low, or the recording software may recognize that the disk is not qualified and refuse to use it.
ATA, formerly known as IDE or EIDE. 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.
SCSI is commonly regarded as an old interface on the verge of extinction. This is not so. SCSI does allow disks 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. SCSI 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. It is likely that SCSI will continue to be developed for the foreseeable future.
Firewire, or IEEE 1394 (or iLink as Sony call it) is a fast serial interface, meaning that data travels along only one conductor in the Firewire cable. Firewire is fast, if not as fast as modern versions of SCSI, and has a number of features that SCSI lacks:
Self-configuring - no ID numbers to be set by the user.
Hot swap - devices can be connected and disconnected without powering down the system.
Bus power - the cable can transfer power from the host to the peripheral device, although this might not be sufficient for all devices.
Thin, flexible cable and robust connectors.
Target mode - where the internal disk of a computer can be connected to another computer as though it were just an external disk.
There is in fact no such thing as a Firewire disk. Firewire is simply a means of data transfer whereas ATA and SCSI intelligently determine the manner in which the data is allocated to the disk's platters. An external Firewire disk is therefore simply an ATA disk in an enclosure together with a 'Firewire bridge'.
USB is currently not of relevance as a disk interface for audio recording as it is too slow, and faster versions must compete with the longer established Firewire.
It is better to dedicate a separate disk to audio rather than allow audio and software to share disk space. The advantage is that the disk can periodically be erased completely so that excessive fragmentation does not occur. Fragmentation is where the disk is unable to allocate contiguous disk space and occurs when the disk is nearly full or has been used over a long period of time without being completely erased. Discontiguous recording forces the disk mechanism to work harder and the system will be capable of fewer simultaneous tracks under this condition
6. What is 'fragmentation'?
Fragmentation means two things:
1) a condition in which individual files on a disk are not contiguous but are broken up in pieces scattered around the disk
2) a condition in which the free space on a disk consists of little bits of free space here and there rather than only one or a few free spaces.
7. Comment on archiving to CD-ROM.
Until recently, disk storage was too expensive to be able to store or archive a project on the original media. Disks are now cheaper than 2-inch analog tape so this is no longer a restriction. However, the archival life of a recording on disk is currently not adequately proven. Recordings can be archived to tape media, typically Exabyte, or to CD-ROM. Optical storage is felt to provide the best assurance of archival stability. The only problem with CD-ROM is the small amount of data (<700 Megabytes) that each disk can hold. If an archiving utility such as Retrospect is used, then successful restoring of the archive depends on the availability of that software, and compatibility with current systems. It would be doubtful whether this would be so in thirty years time, and the relevance and marketability of a recording could easily last a much longer time than that.
Often when recording to a disk system, there ends up being a lot more audio on the disk than is actually used. For instance, inadequate takes that would have been erased on tape are automatically kept by the disk recording system. Systems often allow unused takes to be selected, then deleted. However, there will also be unused audio remaining that consists of the trimmings from regions of audio that have been 'topped and tailed'. This can amount to a considerable quantity of data, so the system may offer a 'compact' function where the superfluous material is deleted. If so, there should be the provision to retain 'handles'. Handles are sections of audio before the start and after the end of each region that are not actually displayed on the screen and do not sound. These can be useful if it proves necessary to adjust an edit, or to create crossfades. A handle duration of 2 seconds is reasonable for most purposes.
8. What are 'virtual tracks'?
All tape recorders have the same number of inputs, tracks and outputs. Disk recorders have no such fixed relationship. Further than that, beyond the limit of the number of tracks that are replayable simultaneously, many disk recorders can store additional so-called 'virtual' tracks which are in synchronization with the regular tracks, but cannot be allocated to an output. Real tracks and virtual tracks can easily be exchanged. As systems become capable of replaying more and more tracks simultaneously, the relevance of virtual tracks will decrease.
9. What is meant by 'edit density'? What are the implications of high edit density?
When an audio file is recorded, subject to the whims of the SCSI or ATA controller, it is recorded in long contiguous sections on the disk. The disk does not have to work hard to retrieve the data therefore many tracks can be replayed simultaneously. When material is edited, then the regions that are to be replayed are probably not continuous on the disk, so the heads have to move more often to retrieve the data. Ultimately, there can come a point where this affects the number of simultaneous tracks. The term 'edit density' is used to mean the number of regions, their length and proximity to each other (shorter, more densely packed, regions make the disk work harder) and how far they are physically separated on the disk. The greater the edit density, the fewer tracks will play. If high edit density is causing a problem, two or more disks should be used so that tracks can be shared among them.
10. Does the editing and trimming of regions delete audio data from the disk?
When editing and trimming otherwise known as “topping and tailing” the useful regions are separated out, the junk audio remains on the disk, but is silenced. This can be extended to audio that might be useful; you can silence a segment of audio that you don't think you will need, and then retrieve it if you realize that you do.
11. In editing, what is the difference between 'slip' and 'grid' modes?
Slip: Since there is no fixed time relationship between tracks, any track or region can be 'slipped' with respect to the others. If it is known that a region (or whole track if no separate regions have been defined) is in the right place, usually it can be locked so that it can't be slipped accidentally.
Grid: It is usually possible to define a grid, so that regions will always 'snap' to grid positions when moved.
The grid mode tracks will automatically snap to grid postions when moved and in slip mode tracks can be moved to any postion at all.
12. When might it not be possible to create a 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.
13. What is 'bouncing', in the context of mixing?
The term 'bouncing' in multitrack recording normally means mixing together similar tracks, such as backing vocals, onto fewer tracks to free up the original tracks for further recording.
14. What is meant by 'latency'?
On record or playback, the size of the buffer is of no consequence - you just have to wait a little longer between pressing play and hearing audio. When you are overdubbing however, the size of the buffer is critical. Anything over 10 milliseconds is clearly audible, and distracting for the performer. Manufacturers often call this 'latency'. Latency occurs in the sound card, in the software itself, and in the buffer, and without doubt it SUCKS.
15. What is the difference between DSP processing and host-based processing?
'Host based processing' is where the computer's own processor performs calculations. In use, you would find that a number of plug-ins can be inserted, but there comes a point where the system can't perform, and (hopefully) it informs you that you have asked too much and a plug-in needs to be removed. There is only one way to increase the performance of a host-based system, other than replacing the computer with a faster one. That is to set up a larger 'buffer'.
The alternative to host-based processing is DSP, or digital signal processing. Audio signals are different in structure from standard computer data and benefit from having DSP chips specially designed for the purpose. The latency of a DSP-based system is very low, of the order of 3 to 4 milliseconds, which for most purposes is unnoticeable. The cost of a DSP-based system may be considerable, but the benefits of eliminating problems due to latency are great.
16. Was DAT originally intended as a professional or a domestic recording medium?
The original purpose of DAT (Digital Audio Tape) was to be a replacement for the Compact Cassette (or simply 'cassette', as we now know it). DAT was intended for domestic recording medium.
17. What is the sampling rate of standard DAT?
The standard DAT format uses 16 bit sampling at a sampling frequency of 48 kHz.
18. What is the resolution of standard DAT?
24 bit high resolution 16 bit resolution standard
19. What is 'azimuth recording'?
The ‘azimuth’ of a tape head refers to the angle between the head gap, where recording takes place, and the tape track itself. In an analog recorder the azimuth is always adjusted to 90 degrees, so that the head gap is at right angles to the track
20. Describe the head wheel in DAT recorder.
In DAT, which uses two heads, one head is set at -20 degrees and the other to +20 degrees, and they lay down tracks alternately. So on playback, each head receives a strong signal from the tracks that it recorded, and the adjacent tracks, which are misaligned by 40 degrees, give such a weak signal that it can be rejected totally.
21. What is SCMS?
Serial Copy Management System
SCMS was developed in response to record companies' needs to protect their copyright. DAT was, and is, capable of making near-perfect digital copies of CDs. Many CDs have their copy-protect flag set so that a DAT machine will not copy them digitally, but it is always possible to copy a CD in the analog domain, with little quality loss. From then on however, an unlimited number of generations of copies can be made from that first DAT, all - allowing for a little error concealment - digitally perfect.
SCMS restricts digital copying by setting certain bits in the data stream. There are three options:
Copy permit - a recording can be copied freely. Only professional machines allow this code to be set.
Copy restrict - a recording can be copied once, then its SCMS bits are set to...
Copy prohibit. Digital copying is not allowed.
22. Describe in what conditions a DAT recorder may be capable of near-simultaneous off-tape recording?
DAT, like the Compact Disc, uses a technique called Double Reed-Solomon Encoding which duplicates much of the audio data, in fact 37.5%, in such a way that errors can be detected, then either corrected completely or concealed so that they are not obvious to the ear. If there is a really huge drop-out on the tape, then the DAT machine will simply mute the output rather than replay digital gibberish
23. What is the sub-code area of the DAT tape used for?
Sub Code areas allow extra data to be recorded alongside the audio information. Not all of the capacity of the Sub Code areas is in use as yet, allowing for extra expansion of the DAT system. Those at present in use include:
A-time, which logs the time taken since the beginning of the tape
P-time, which logs the time taken since the last Start ID.
Start ID marks the beginning of each item;
Skip ID tells the machine to go directly to the next Start ID, thus performing an ‘instant edit’.
End ID marks the end of the recording on the tape.
24. What is 'interleaving'?
As an extra precaution against dropouts, another technique called interleaving is employed which scatters the data so that if one section of data is lost, then there will be enough data beyond the site of the damage which can be used to reconstruct the signal.
25. What is the width of the tape used for 24-track DASH?
24-track machines use the normal density geometry on 1/2” tape, which allows twenty-four digital audio tracks, two analog cue tracks, a control track and a timecode track.
26. What is the width of the tape used for 48-track DASH?
Same as 24 –track machine
27. Describe how 24-track and 48-track DASH machines are compatible.
DASH-format machines are backward compatible: 24-track machines can be used with newer models, and a project can be started on a 24-track machine and completed on a 48-track recorder, if needed, as the data from tracks 25-48 are written into the spacing between the original 24 tracks. In addition to 24-track or 48-track recording, DASH format provides two analog cue tracks and one track each for control and timecode sig-nals.
28. How are DASH tapes edited?
Digital tape recording systems such as DASH can be edited by copying the tape.
29. In DASH, why does a playback head come before the record head in the tape path?
The first head is a playback head, which on an basic DASH machine is followed a record head only. Analog processes take place virtually instantaneously, digital operations take a little time. There will be a slight delay while the playback signal is processed, and another delay while the record signal is processed and put onto tape. 105 milliseconds in fact, which corresponds to about 75 mm of tape. To perform synchronous overdubs there has to be a playback head upstream of the record head otherwise the multitrack recording process as we know it just won’t work.
30. Comment on the cleaning requirements of DASH
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 analog records will clog a DASH head with their fibers
31. How many tracks does a modular digital multitrack (MDM) have?
Formats capable of 8 tracks.
32. How can more tracks be obtained?
Multiple machines can be easily synchronized to give more tracks.
33. Comment on the types of usage of ADAT and DTRS machines?
Recordings are made on commonly available video tapes: ADAT takes S-VHS tapes, DTRS takes Hi-8
Tape need to be formatted before use. Formatting can take place during recording, but this is only appropriate when a continuous recording is to be made for the entire duration of the tape.
Very maintenance-intensive. For a 24-track system, four machines (4 x 8 = 32) are necessary to account for the one that will always be on the repair bench.
High resolution versions available (ADAT 20-bit, DTRS 24-bit, 96 kHz, 192 kHz, with reduced track count)
The differences are these:
Maximum record time: ADAT - 60 minutes, DTRS - 108 minutes
ADAT popular in budget music recording studios
DTRS popular in broadcast and film post-production
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Sat Apr 24, 2004 5:48 am |
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