AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 10 - MIDI |
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1. Explain why it is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously.
2. Explain why some multitrack hard disk recording systems can play back much slower than normal speed, but only a little faster.
3. State TWO major advantages of hard disk recording systems over digital tape recorders.
4. Describe THREE major operational advantages of having two modular digital multitrack recorders such as the ADAT or DTRS formats over a format which records sixteen tracks on the same tape on a single machine.
5. Explain why the punch in process on a hard disk recorder is more flexible than that on an analogue or digital tape recorder.
6. With reference to an analogue multi-track recorder briefly explain
a) the term `sync' output
b) why the `sync' output is required when overdubbing.
7. It is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously. Why is this?
8. Some hard disk recording systems have mixing facilities so that several tracks can be mixed into a stereo output. If no other outputs are available why must the system incorporate reverb internally?
9. What are the two major advantages of hard disk recording systems over digital tape recorders?
10. What piece of equipment is necessary to use a sequencer with a multitrack tape recorder?
b) Why is it preferable to use MTC rather than MIDI clocks and Song Position Pointers when synchronising a sequencer to a tape recorder?
c) If MIDI Machine Control (MMC) is not used, describe briefly the two distinct stages of operation when recording a piece of sequenced music to multitrack tape.
d) What is the advantage of MMC?
e) In a system using MMC, while playback or recording progresses the multitrack and sequencer will be running in sync. At this moment which is master and which is slave?
11. You have been given an unlabelled tape to play which starts with a warbling tone. What noise reduction system might have been used?
b) You have been given an unlabelled tape to play which starts with noise. What noise reduction system might have been used?
c) Name three domestic noise reduction systems invented by the Dolby company.
d) Give the name of another fairly common analogue noise reduction system.
e) Where would you find the ATRAC digital noise reduction system?
12. When recording onto analogue or digital multitrack tape, in a situation where synchronisation is going to be used, what procedure must be carried out before any recording can begin?
b) Your studio manager has given you a multitrack tape containing music and timecode to copy. What must you do to ensure that the timecode is copied correctly?
c) A multitrack tape of a band with no sequenced instruments was striped with timecode at the start of the session and has subsequently been edited? Would it be good practice to use the existing timecode as a synchronisation reference for the console automation system during the mix?
d) Referring to c) above, why would it not be a problem to re-stripe the tape with timecode and erase the original timecode, even if the generator does not have a jam sync function?
e) You have striped timecode on track 24 of an analogue tape and recorded a bass guitar on track 23. When you try and synchronise a MIDI sequencer using a cheap timecode to MTC convertor, the sequencer often stops or loses sync. Why?
13. When working with MIDI and multitrack tape, does the multitrack recorder synchronise to the sequencer or does the sequencer synchronise to the multitrack tape?
b) When working with an ADAT recorder, why wouldn’t you necessarily have to stripe the tape with timecode to synchronise a sequencer?
c) Imagine that several tracks of a MIDI sequence have been transferred to multitrack tape. The producer decides that he wants to varispeed the tape a little faster. Should this be done before or after the remaining sequencer tracks have been transferred to tape? Explain your answer.
14. Noise reduction systems such as dbx and Dolby cause the noise level in a recording to vary. Explain why this is so.
15. You have been asked to remix a song (in the sense of creating a completely new version) originally made on multitrack tape in the early 1970s.
a) What would be the main problem in synchronising a sequencer to the original tape?
b) If you decided only to use the vocal track from the original recording, how would you make the lines fit in time with your new MIDI sequencer arrangement?
c) Suppose you want the song to be around 15% faster in tempo. What should you do to speed up the vocals?
d) The record company decides that it wants to keep a lot of the original instrumentation, but also likes your strict tempo MIDI sequence. What type of equipment should you use to put everything together?
16. You are working with a multitrack recorder that will slave to SMPTE/EBU timecode from (for instance) a video machine, but has no other means by which it may be externally controlled. Imagine you stop the master machine, rewind the tape to the beginning and start playing. What will the multitrack do?
17. What is the frame rate of NTSC?
18. What is the frame rate of PAL (and SECAM)?
19. What is 'drop frame timecode'?
20. Comment on the requirements for recording timecode onto analog tape
21. Comment on the problems that occur when using timecode on analog tape
22. Why must timecode be regenerated when it is copied?
23. What is an 'offset'?
_________________
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 31, 2005 11:37 am |
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AndyBarber
Joined: 09 Sep 2005
Posts: 18
Location: North Wales |
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Posted: Mon Oct 31, 2005 9:37 pm Post subject: Week 10 - MIDI
ANDY BARBER
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1. Explain why it is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously.
The use of ‘virtual’ tracks allow the recording of multiple takes of a track of which the best can be selected and played back. You can have a number of virtual tracks (usually  for every physical channel. Much more flexible than a tape system.
2. Explain why some multitrack hard disk recording systems can play back much slower than normal speed, but only a little faster.
The speed in which the hard disk can read and playback audio data is limited. Playing back at a higher speed will push the hard drive to its limit ultimately reaching its maximum access time. Playing back at slow speeds is easy as hard drive has plenty of time to read the audio data.
3. State TWO major advantages of hard disk recording systems over digital tape recorders.
Hard disks are random-access systems meaning data can be accessed at random with only a short delay
Tape drives are linear access and have to be winded to reach the required data.
Hard drive systems have a more advanced editing capabilities with a higher density data storage
4. Describe THREE major operational advantages of having two modular digital multitrack recorders such as the ADAT or DTRS formats over a format which records sixteen tracks on the same tape on a single machine.
Modular digital multitrack - ADAT and DTRS are 8-track digital tape recording system
- If a tape gets damaged only half the audio data will be lost
- With two 8 track tape machines its is easily possible to make a complete backup of a tape
- Sub mixes from the first tape can be recorded onto the second tape freeing up tracks on the first machine
5. Explain why the punch in process on a hard disk recorder is more flexible than that on an analogue or digital tape recorder.
Punch in-out recording makes it possible to replace a certain part of a track with a new recording with rest of track untouched. Punching in - setting recording to begin at a specific location in a track
With a tape, when a punch in recording is made it is recorded over the top of the existing original recording. With a hard drive setup the new data is recorded in a new location on the drive not over the top of the original. Punch in/out recording on a hard disk is non destructive. Multiple punch in/out recordings can be made allowing more control when editing.
6. With reference to an analogue multi-track recorder briefly explain
a) the term `sync' output
This is when the recording head in an analogue tape system is used for playback. This removes the time delay between the record head and the normal playback head. This is known as a sync output
b) why the `sync' output is required when overdubbing.
The sync output ensures any overdubbing is in sync with the rest of the audio on the tape
7. It is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously. Why is this?
SEE Q1
8. Some hard disk recording systems have mixing facilities so that several tracks can be mixed into a stereo output. If no other outputs are available why must the system incorporate reverb internally?
Once a number of tracks are mixed down into one stereo channel they can no longer be enhanced separately. Any effects should be applied to the tracks before they are mixed into one signal. With only one stereo output, tracks cant be enhanced by external ‘send’ effects and sent back to recorder.
9. What are the two major advantages of hard disk recording systems over digital tape recorders?
SEE Q3.
10. a) What piece of equipment is necessary to use a sequencer with a multitrack tape recorder?
If a software sequencer is being used then a MIDI interface is required. A time code generator is required to provide a tape sync message. This is a special audio signal created by a MIDI device that is recorded onto one track of the multitrack tape. With an analogue multitrack a timecode converter is required to convert SMPTE in MTC.
b) Why is it preferable to use MTC rather than MIDI clocks and Song Position Pointers when synchronising a sequencer to a tape recorder?
MTC is a timecode measured in absolute time. It allows a track to be played back from any point on the tape. MIDI clock and SPP are a measure of relative time (no positional data) and if recorded onto tape, the sequencer wont know where about in the song to start playing. MTC will also perform better if the code is corrupted.
c) If MIDI Machine Control (MMC) is not used, describe briefly the two distinct stages of operation when recording a piece of sequenced music to multitrack tape.
MMC is a popular means of remote control for modular multitrack recording equipment
MMC can control basic transport functions of tape machine/hard disk from a MIDI port
Without a MMC code;
Tape must firstly be striped with an SMPTE timecode on one of its tracks, setting up multitrack as the master. The SMPTE code must then be sent to the sequencer, converted to MTC by a timecode converter
d) What is the advantage of MMC?
Automatically controls transport functions of all connected devices, keeping them in sync with each other
e) In a system using MMC, while playback or recording progresses the multitrack and sequencer will be running in sync. At this moment which is master and which is slave?
Sequencer is the master with multitrack as slave.
11.
a) You have been given an unlabelled tape to play which starts with a warbling tone. What noise reduction system might have been used?
Dolby A creates a warbling tone which is an alignment signal coming from the encoding processor. The signal is put at the start of the tape so it can be used to calibrate the decoding process.
b) You have been given an unlabelled tape to play which starts with noise. What noise reduction system might have been used?
Dolby SR uses a pink noise signal as the alignment signal.
c) Name three domestic noise reduction systems invented by the Dolby company.
Dolby employs circuitry that pre-emphasizes high frequencies before they are recorded onto tape in order to make them larger than the tape hiss noise with which they compete.
Dolby B - most widespread, used in popular tape decks
Dolby C - most recent, involves double compression
Dolby S - home entertainment version of Dolby SR
(Dolby A - professional level, used in high speed multitrack machines)
d) Give the name of another fairly common analogue noise reduction system.
Dbx system is a linear compression-expansion system
- Amplifies high frequencies when encoding recording signal
- filtering the high frequencies when decoding or playing back the signal.
e) Where would you find the ATRAC digital noise reduction system?
(Adaptive TRansform Acoustic Coding)
Used on Mini disks and other Sony-branded audio players
12.
a) When recording onto analogue or digital multitrack tape, in a situation where synchronisation is going to be used, what procedure must be carried out before any recording can begin?
An SMPTE timecode signal must be recorded/striped onto one of the tapes channels before recording
b) Your studio manager has given you a multitrack tape containing music and timecode to copy. What must you do to ensure that the timecode is copied correctly?
When copying it must be done in real time with both recorders running at the same speed so that timecode signal isn’t distorted. The ‘jam sync’ (regeneration) function must be used when copying time code as timecode degenerates quickly when a copy is made.
c) A multitrack tape of a band with no sequenced instruments was striped with timecode at the start of the session and has subsequently been edited? Would it be good practice to use the existing timecode as a synchronisation reference for the console automation system during the mix?
If the tape has been edited (parts removed/cut and pasted) then the timecode would no longer be constant and should not be used as a reference for synchronisation. Best to re record the timecode.
d) Referring to c) above, why would it not be a problem to re-stripe the tape with timecode and erase the original timecode, even if the generator does not have a jam sync function?
The timecode may have been altered but the song will still be running at the same constant tempo. No instruments are being synchronised so a new timecode can be added after editing from the start of the song.
e) You have striped timecode on track 24 of an analogue tape and recorded a bass guitar on track 23. When you try and synchronise a MIDI sequencer using a cheap timecode to MTC convertor, the sequencer often stops or loses sync. Why?
With analogue tape, magnetic data from one track on the tape can spill over and be picked up on adjacent tracks causing signal interference. Crosstalk onto timecode track will cause these problems.
13.
a) When working with MIDI and multitrack tape, does the multitrack recorder synchronise to the sequencer or does the sequencer synchronise to the multitrack tape?
The best method of sync involves converting SMPTE/EBU timecode on the tape to MIDI timecode (MTC) for the sequencer to follow. The sequencer should be synchronised to the multitrack
b) When working with an ADAT recorder, why wouldn’t you necessarily have to stripe the tape with timecode to synchronise a sequencer?
ADATS have their own optical/digital and synchronization interface with an internal word clock, easily integrating them into an existing system with sample-accurate sync.
c) Imagine that several tracks of a MIDI sequence have been transferred to multitrack tape. The producer decides that he wants to vary the speed of the tape a little faster. Should this be done before or after the remaining sequencer tracks have been transferred to tape? Explain your answer.
Varying the speed of the tape machine will change the pitch of the tracks recorded on the tape. Its best to copy all tracks first so that when the tape is speeded up, all tracks will be stretched equally and will remain in tune relative to each other.
14. Noise reduction systems such as dbx and Dolby cause the noise level in a recording to vary. Explain why this is so.
When recording a compressor is used to reduce the difference between the loudest and quietest sound permitting the optimum recording level for the signal When playing back an expander is used to create the original dynamic range with quieter passages having less background noise. The noise in louder sections is louder too but is masked by the desired part of the signal.
15. You have been asked to remix a song (in the sense of creating a completely new version) originally made on multitrack tape in the early 1970s.
a) What would be the main problem in synchronising a sequencer to the original tape?
MIDI sequencers didn’t exist in the 1970s so the song would not have been recorded with this remix in mind. SMPTE timecode was created in 1967 so would have been used on the tape. The main problem would be with the quality of the striped timecode track as the tape may have deteriorated with time. Synchronization problems would also occur if the music was recorded without a metronome/click track as the tempo might not be constant.
b) If you decided only to use the vocal track from the original recording, how would you make the lines fit in time with your new MIDI sequencer arrangement?
I would record all of the vocal track and import it as a digital audio file in the sequencer. From there it can be easily edited/time stretched to fit the timing and tempo of the remix track.
c) Suppose you want the song to be around 15% faster in tempo. What should you do to speed up the vocals?
I would record the vocals with the tape playing at a higher speed so the increase in tempo can be achieved. A automatic pitch shifter can then be used to correct the vocal frequency.
d) The record company decides that it wants to keep a lot of the original instrumentation, but also likes your strict tempo MIDI sequence. What type of equipment should you use to put everything together?
I would bounce each track off the tape in turn as individual audio tracks into a MIDI/Audio sequencer. Once done they can be edited and played back at any desired tempo.
16. You are working with a multitrack recorder that will slave to SMPTE/EBU timecode from (for instance) a video machine, but has no other means by which it may be externally controlled. Imagine you stop the master machine, rewind the tape to the beginning and start playing. What will the multitrack do?
The multitrack would also rewind and start playing at the same point and time as the master. This is because the multitrack is receiving a timecode which specifies exactly where its position is in the song.
17. What is the frame rate of NTSC? (National Television System(s) Committee)
Converting between digital and audio sample rates and video frames need to be accurate enough to ensure audio/video sync relationship.
The NTCS frame rate is 29.97 FPS
18. What is the frame rate of PAL (and SECAM)? (phase-alternating line)
PAL video frame rate is a true 25 FPS:
SECAM (European colour TV standard) also 25 FPS
19. What is 'drop frame timecode'?
Monochrome TV programs run at exactly 30FPS, where as colour TV runs at 29.97FPS. This creates a flaw in synchronisation of 3.6 seconds per hour playback
In order to accommodate colour information the old monochrome frame rate for television had to be changed from 30 FPS to 29.97 FPS. In order for 30fps timecode could be made synchronous with new rate the following modifications were required
With NTSC running at 30 frames per second causes an excess of 108 frames per hour.
To eliminate 108 frames an hour, 2 time code frame values are dropped each minute (120 in total) except every 10th minute (120 - (2 x 6) =108).
Results in minimum long term drift between timecode and picture
20. Comment on the requirements for recording timecode onto analog tape
Tape speed must be kept at a constant rate. During playback a device (sync stripper) isolates a sync pulse out of the timecode signal and sends it to a resolver unit which controls the precise speed of the tape by comparing signal to a reference signal. This allows tape to playback at different tempos like 29.97 FPS.
When recording an audio tone (linear time code) from a timecode generator, signal must be strong giving good SNR. The standard level is -10dBv ensuring signal is hot enough to be read but not so hot to cause excessive crosstalk to adjacent tracks.
Always record onto an edge track trying to leave the adjacent track unused (guard track)
21. Comment on the problems that occur when using timecode on analogue tape
Incorrect recording of timecode can make it difficult for slave to read code.
Crosstalk problems occur if sync signal recorded to loud.
22. Why must timecode be regenerated when it is copied?
The signal quality of the time code recorded onto analogue tape is slightly degraded and will continue to degrade with each copy made of the tape
SMPTE regenerators can be used to solve this problem
23. What is an 'offset'?
Some times you may wish to offset the position of two devices with respect to each other but still in sync with each other. Offsets can be positive or negative, use the following rule
Time Code In + Time Code Offset = Transport Position
http://www.atariage.com/common/video_key.html
http://www.answers.com/ATRAC
http://home.earthlink.net/~rongonz/home_rec/background.html
http://teamcombooks.com/mp3handbook/14.htm
http://www.equipmentemporium.com/introtimecode.htm
http://www.audiomasterclass.com/library/recordingtechniques/4midiandmultitrack.html
http://www.sfu.ca/sca/Manuals/ZAAPf/n/noise_reduction.html
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/tape5.html#c4
http://www.xowave.com/doc/recording/timecode.shtml |
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Fri Nov 04, 2005 12:49 pm |
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Polarman
Joined: 24 Jun 2005
Posts: 55
Location: Barbados |
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1. Explain why it is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously.
It is common for multitrack hard disk recorders to store more tracks in synchronisation than it can play simultaneously. You can find in specifications that it is a 32-track recording studio and that it is able to record up to 272 tracks. The reason for this is that you are able to record multiple takes on each track and save that. Later in the mixing stage you can use the best parts from each track. A multitrack hard disk recording system can have for example 8 virtual tracks for each track. That means that you can play any combination of this 8 virtual track one track. So for example: Thirty-two physical tracks plus a stereo master track for mixdown (all have 8 virtual tracks per) gets you a total of 272 tracks.
http://www.zzounds.com/item--KORD3200
2. Explain why some multitrack hard disk recording systems can play back much slower than normal speed, but only a little faster.
The reason why some multitrack hard disk recording systems can play back much slower than normal speed, but only a little faster is that slower playback demands less CPU power and disk speed, disk buffer than a faster playback. Normally multitrack hard disk recording systems are built only for a reason amount of faster play back.
3. State TWO major advantages of hard disk recording systems over digital tape recorders.
- A hard disk recording system can record more tracks. That means no bouncing.
- The fast and non-destructive edit function on hard disk recoding systems is a big advantage.
4. Describe THREE major operational advantages of having two modular digital multitrack recorders such as the ADAT or DTRS formats over a format which records sixteen tracks on the same tape on a single machine.
Three major operational advantages of having two 8 tracks instead of one 16 track:
- You will have almost endless amount of tracks since you can change cassettes and continue to record using bouncing.
- Easy to take back up of the tapes
- Editing is easier since you can bounce from one machine to the other.
5. Explain why the punch in process on a hard disk recorder is more flexible than that on an analogue or digital tape recorder.
The main difference is that the recording process is not destructible. The punch ins doesn’t have to be made in exact timing it can be edited afterwards or just be redone.
6. With reference to an analogue multi-track recorder briefly explain
a) the term `sync' output
The outputs of a professional analogue multi-track recorder can be switched between three different modes: Input, Reproduce and Sync. The term “sync” output comes from selective synchronisation or sel-sync. The sync mode lets the track be played back by its record head (Huber & Runstein, 2005).
b) why the `sync' output is required when overdubbing.
When overdubbing you normally have to monitor previously recorded track to play along to. Overdubbing one or more tracks while listening to previously recorded tracks through the playback head will cause the newly recorded tracks to be out of sync in the final playback. To avoid this sync problem the tracks to be monitored has to be set to sync mode. This lets the tracks being played back by their respective record head tracks. In this way the record head will both record and play back their respective tracks there is no signal delay (Huber & Runstein, 2005)
7. It is common for a multitrack hard disk recording system to be able to store more tracks in synchronisation than it can play simultaneously. Why is this?
It is common for multitrack hard disk recorders to store more tracks in synchronisation than it can play simultaneously. You can find in specifications that it is a 32-track recording studio and that it is able to record up to 272 tracks. The reason for this is that you are able to record multiple takes on each track and save that. Later in the mixing stage you can use the best parts from each track. A multitrack hard disk recording system can have for example 8 virtual tracks for each track. That means that you can play any combination of this 8 virtual track one track. So for example: Thirty-two physical tracks plus a stereo master track for mixdown (all have 8 virtual tracks per) gets you a total of 272 tracks.
http://www.zzounds.com/item--KORD3200
8. Some hard disk recording systems have mixing facilities so that several tracks can be mixed into a stereo output. If no other outputs are available why must the system incorporate reverb internally?
To be able to use an external reverb there is a need for a send, auxiliary sends or an output. If the hard disk recording system only have one stereo output both outputs are used for mixing down to two track. Therefore to be able to add reverb the reverb has to be incorporated internally.
9. What are the two major advantages of hard disk recording systems over digital tape recorders?
- A hard disk recording system can record more tracks. That means no bouncing.
- The fast and non-destructive edit function on hard disk recoding systems is a big advantage.
10. What piece of equipment is necessary to use a sequencer with a multitrack tape recorder?
To be able lock a sequencer to a multitrack tape a SMPTE-to MTC converter is needed. The SMPTE-to MTC converter will generate the SMPTE tone that should be striped on to the tape then it will convert this tone to MTC back to the sequencer (Huber & Runstein, 2005).
b) Why is it preferable to use MTC rather than MIDI clocks and Song Position Pointers when synchronising a sequencer to a tape recorder?
MTC is used instead of MIDI Clocks and Song Position Pointers when real time synchronisation is important and not beats or note values. This can be for example when synchronising for video. With timecode the locations will remain in the same place even if the musical tempo is changed. That is not the case with MIDI Clocks and song position pointers (Rumsey, 2004).
c) If MIDI Machine Control (MMC) is not used, describe briefly the two distinct stages of operation when recording a piece of sequenced music to multitrack tape.
The first stage is to stripe the highest track on the tape with ascending code from the tapes beginning to the end. Then the code can be routed to the SMPTE interface. Or a box that converts SMPTE to MTC which then can be plugged into a MIDI interface in to the DAW or sequencer. (Rumsey, 2004). When using a sequencer together with a multi track tape it is very important that the synchronisation is correct. It’s very hard and costly to sync the multitrack recorder to the sequencer since the tape will fluctuate in speed. Therefore is desirable to synchronise the sequencer to the multitrack (Huber & Runstein, 2005).
d) What is the advantage of MMC?
The MMC protocol lets you remotely control DAWs, MIDI sequencers, hard-disk recorders, tape and video transports etc from a hardware device or a computer program via MIDI. The advantages are mainly two; everything is controllable from one single device and different functions can be pre-programmed and automated (Huber & Runstein, 2005).
e) In a system using MMC, while playback or recording progresses the multitrack and sequencer will be running in sync. At this moment which is master and which is slave?
This system is setup so the sequencer is the master regarding MMC commands. When play is pushed on the sequencer the MMC command transmits to the multitrack to start. The multi track will send out SMPTE converted to MTC that the sequencer will chase. So to answer the question when the sequencer and the multitrack is running in sync the multi track is the master (Rumsey, 2004).
11. You have been given an unlabelled tape to play which starts with a warbling tone. What noise reduction system might have been used?
If I play a tape that starts with a warbling tone I am hearing the alignment signal for Dolby A from the encoding processor which is recorded at the start of the tape and used to calibrate the decoding process on replay.
http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html
b) You have been given an unlabelled tape to play which starts with noise. What noise reduction system might have been used?
If I play a tape that starts with noise (pink) I am hearing the alignment signal for Dolby SR from the encoding processor which is recorded at the start of the tape and used to calibrate the decoding process on replay.
http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html
c) Name three domestic noise reduction systems invented by the Dolby company.
a. Dolby B
b. Dolby C
c. Dolby S.
http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html
d) Give the name of another fairly common analogue noise reduction system.
Another fairly common analogue noise reduction system is dbx. It uses a fixed-ratio compressor to reduce the dynamic range of the signal to be recorded (primarily by increasing the level of quiet signals). On replay, a matching expander pushes low-level signals even lower, with the aim of recreating the original signal dynamics and reducing the tape noise correspondingly
http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html
e) Where would you find the ATRAC digital noise reduction system?
The MD format employs data reduction to decrease the amount of data saved on disc by a factor of five. Uses ATRAC (Adaptive TRansform Acoustic Coding) algorithm to do this. ATRAC applies high-complex digital signal processing according to a model for human hearing, coding the signal so that redundant or inaudible information can be omitted, thus reducing the number of bits needed to store it
http://www.minidisc.org/format_wars.html
12. When recording onto analogue or digital multitrack tape, in a situation where synchronisation is going to be used, what procedure must be carried out before any recording can begin?
The first stage is to stripe the highest track on the tape with ascending code from the tapes beginning to the end. Then the code can be routed to the SMPTE interface. Or a box that converts SMPTE to MTC which then can be plugged into a MIDI in to the DAW or sequencer. It’s always cheaper to let the sequencer or the DAW act a slave and the tape act as master (Rumsey, 2004).
b) Your studio manager has given you a multitrack tape containing music and timecode to copy. What must you do to ensure that the timecode is copied correctly?
To ensure that the timecode is copied correctly jam sync can be used but under normal circumstances the time code refresher should be enough. The time code refresher reads, amplifies and then regenerates the square wave back to its original shape. If after checking the time code and you find that slaves stops then you have to use jam sync. Jam sync mode on the synchroniser outputs the next time code value even if has not appeared on the input. Jam sync only works with short dropouts though (Huber & Runstein, 2005).
c) A multitrack tape of a band with no sequenced instruments was striped with timecode at the start of the session and has subsequently been edited? Would it be good practice to use the existing timecode as a synchronisation reference for the console automation system during the mix?
Since the tape has been edited there is no continuous time code on the tape. The best thing to do is record a new time code.
d) Referring to c) above, why would it not be a problem to re-stripe the tape with timecode and erase the original timecode, even if the generator does not have a jam sync function?
Since there are no sequenced instruments on the tape there is no use for the old time code. A totally new time code can be recorded.
e) You have striped timecode on track 24 of an analogue tape and recorded a bass guitar on track 23. When you try and synchronise a MIDI sequencer using a cheap timecode to MTC convertor, the sequencer often stops or loses sync. Why?
This is a problem of crosstalk between channels. This can be of two reasons. The level of time code can recorded at a level to low or your MTC converter is to sensible. If it worked before recording the bass guitar record the bass on another track and leave track 23 empty.
13. When working with MIDI and multitrack tape, does the multitrack recorder synchronise to the sequencer or does the sequencer synchronise to the multitrack tape?
When using a sequencer together with a multi track tape it is very important that the synchronisation is correct. It’s very hard and costly to sync the multitrack recorder to the sequencer since the tape will fluctuate in speed. Therefore is desirable to synchronise the sequencer to the multitrack. The sequencer reads the converted SMPTE as MTC (Huber & Runstein, 2005).
b) When working with an ADAT recorder, why wouldn’t you necessarily have to stripe the tape with timecode to synchronise a sequencer?
An ADAT recorder has a built in sync signal which has almost sample accuracy. The synchronisation ports are used to transmit a proprietary code for locking multiple devices together. This code is also used to synchronise to fro example a sequencer but needs to be converted to SMPTE or MTC using a ADAT sync interface (Huber & Runstein, 2005).
c) Imagine that several tracks of a MIDI sequence have been transferred to multitrack tape. The producer decides that he wants to varispeed the tape a little faster. Should this be done before or after the remaining sequencer tracks have been transferred to tape? Explain your answer.
If you varispeed the tape the tracks on the tape will change in pitch but the tracks played by the sequencer will not. To keep the same pitch change for all tracks, all tracks should be on the tape before varispeeding the tape.
14. Noise reduction systems such as dbx and Dolby cause the noise level in a recording to vary. Explain why this is so.
The filter(s) in noise reduction systems is side chained so they only work on high level signals in their respective frequency band. The lack of noise reduction on high levels does not matter since high level signal masks low-level noise. So the noise level is actually higher on high levels then on low levels (Rumsey, 2004).
15. You have been asked to remix a song (in the sense of creating a completely new version) originally made on multitrack tape in the early 1970s.
a) What would be the main problem in synchronising a sequencer to the original tape?
The main problem would be the timing of the tape. If the tape doesn’t have a click track or timecode you will have to stripe the tape with a new time code if there is a free track left. To avoid problems I would import all tracks into a sequencer. In this way I can built a tempo track that fits the drum tracks.
b) If you decided only to use the vocal track from the original recording, how would you make the lines fit in time with your new MIDI sequencer arrangement?
I would import the vocal track into my sequencer and adjust the vocal there. Checking the wave file from the vocal makes it easy to find the tempo. I can slave the tempo track to the vocal or I can correct the vocal to a more modern quantised feel.
c) Suppose you want the song to be around 15% faster in tempo. What should you do to speed up the vocals?
To change a tempo on a wav file you can use a time stretch tool. Normally maximum change of a wav files tempo without changing the pitch is 10% before serious quality loss occur. If it sounds well in after changing the tempo15% it is ok…
d) The record company decides that it wants to keep a lot of the original instrumentation, but also likes your strict tempo MIDI sequence. What type of equipment should you use to put everything together?
As I said in a) I would bring all tracks over to the digital domain. I would use a MIDI/Audio sequencer to bring everything together. If they want a strict quantised feel I have to lock the wave files to a strict tempo. I can for example use warp feature in Cubase SX to lock each track to the MIDI tempo track. The result would be a remix that has a strict tempo all through. No fluctuations in tempo.
16. You are working with a multitrack recorder that will slave to SMPTE/EBU timecode from (for instance) a video machine, but has no other means by which it may be externally controlled. Imagine you stop the master machine, rewind the tape to the beginning and start playing. What will the multitrack do?
The multitrack will stop when the master machine is stopped. It will still be stopped while rewinding the video tape. When play is pressed on the video machine the multitrack will immediately rewind and chase the video machine to get back in sync.
17. What is the frame rate of NTSC?
The frame rate of NTSC is 29.97 fps.
18. What is the frame rate of PAL (and SECAM)?
The frame rate of PAL (and SECAM) is 25 fps.
19. What is 'drop frame timecode'?
Before colour TV in USA was introduce the frame rate was 30 fps on the black and white transmission. The reason for 30fps was that it was lock to the mains frequency of 60 HZ. When colour TV was introduced it was proved that it was necessary to change the frame rate slightly in order to accommodate the colour information within the same spectrum. Since there was no longer need to lock the frame rate to the mains frequency because of improvements in oscillator stability the 30fps could be made synchronous only if if it dropped two frames every minute except for every tenth minute. This resulted in a minimal long-term drift between the picture and the timecode (75ms over 24 hours). The drift is reset every minute. When a recording is expected to be used for a NTSC video programme the “drop frame” should be set used (Rumsey, McCormick, 2004).
20. Comment on the requirements for recording timecode onto analog tape
The tape should be striped with code from beginning to the end all the way. The code should be recorded around -5 to -10 dB on the edge (outside) track (Rumsey, McCormick, 2004) (Huber & Runstein, 2005).
21. Comment on the problems that occur when using timecode on analog tape
The biggest problem I crosstalk between tracks or cables due to the very audible mid-frequency of the timecode. It is very important that the time code is recorded at the accurate level otherwise difficulty in tracking can occur (Rumsey, McCormick, 2004).
22. Why must timecode be regenerated when it is copied?
The time code is a square –wave waveform and this is difficult to record on an analogue tape and it will be distorted. Time code readers can handle this and a relatively tolerant. When the code is copied from tape to tape for one or several generations the distortion gets worse and can result in a useless code. To avoid this, a time code refresher is often incorporated in most time code synchronisers and MIDI interfaces which have sync capabilities. The process reads the degraded time code information that has benne previously recorded and then amplifies and regenerates the square wave back to it original shape. The code can now be freshly recorded to a new track.
(Rumsey, McCormick, 2004)
23. What is an 'offset'?
An offset is the relative time between a master and a slave. IF a recording of a song starts on a tape recorder at 00:07:21:07 the off set to the slave is set to the same. This means that the slave will start at the beginning of the song.
(Rumsey, McCormick, 2004)
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SOURCES:
Huber, D.M., & Runstein, R.E. (2005). Modern Recording Techniques, 6th ed. Focal Press: Burlington
Rumsey, F. (2004). Desktop Audio Technology: digital audio and MIDI principles. Focal Press:Oxford.
Rumsey, F. & McCormick, T. (2004). Sound and Recording: An Introduction, 4th ed. Oxford: Focal Press
http://www.zzounds.com/item--KORD3200
http://www.soundonsound.com/sos/1997_articles/may97/analysinganalogue.html
http://www.minidisc.org/format_wars.html |
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Sat Nov 05, 2005 9:44 pm |
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