AUdIoCoUrSeS
Joined: 31 Oct 2002
Posts: 2014
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| Week 4 - Equipment 1 |
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1. What is the function of mixing desk automation?
2. Why might the faders have to be moved during the mix?
3. What aspects of mixing would normally be automated on an analogue console?
4. Comment on VCA vs. Moving Fader automation.
5. Describe write/update/read.
6. How does an automated mix session start?
7. How would a section of automation data be re-recorded?
8. How are automation 'punch-ins' blended smoothly with existing data?
9. How could a complex series of moves be increased in level by say 3dB?
10. Describe fader grouping.
11. How could EQ, for instance, be automated using an analogue mixing console?
12. How would EQ be automated using a digital mixing console?
13. What is 'recall'?
14. What advantages does a digital console have over an analogue console regarding recall?
15. Does a compressor act upon loud signals or quiet signals? What does it do to the signals upon which it acts?
18. What is the function of 'make up gain'?
19. How is a compressor usually connected to a mixing console to compress a single signal?
20. How is a compressor connected to a mixing console to compress the entire mix?
21. Explain 'ratio', in the context of compression.
22. Describe the difference between hard knee and soft knee.
23. What are 'breathing' and 'pumping'?
24. What happens if the release time is too long?
25. What does it mean if the gain reduction meter is showing frequent changes?
26. Describe the effect of compression on noise level.
27. Describe the function of the stereo link switch.
28. What is the side chain input?
29. Describe a typical use of the side chain input.
30. Is a noise gate usually effective on a mixed stereo signal?
31. Is a noise gate effective on a signal where the instrument plays all the time?
32. Is a noise gate effective on a single noisy signal where there gaps in the playing?
33. Why is it often considered beneficial to gate some or all of the mics on a drum kit (except the overheads)?
34. How many gates are often used in live sound: none, a few or many?
35. How is the noise gate connected to the mixing console?
36. What is the function of the Threshold control?
37. What is the function of the Range control?
38. Comment on the Attack, Hold and Release (Decay) controls.
39. What would happen if a stereo signal was gated, but the stereo link function was not selected?
40. Why are side-chain filters beneficial?
41. Comment on the use of an external key to improve the reliability of gating.
42. What is an expander?
43. Why are compressors and gates often used together?
44. Comment on envelope shaping using a noise gate.
45. Comment on gated reverb.
_________________
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Mon Sep 27, 2004 12:04 pm |
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kurt53
Joined: 15 Sep 2004
Posts: 6
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| Week4 answers |
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Hi, here are my answers for this week, sorry my other assignments will be posted as soon as I’ve completed them, the past few weeks have been so hectic. I found these questions quite challenging, I know what compression does, but, I still can’t determine where it has been used if I had to listen for it, and the whole automation concept, I found quite interesting, anyway, I got most of my answers from the forums and websites, and some from my head.
1. What is the function of mixing desk automation?
Automation enables changes to be made as you see fit in real time, it also gives you the ability to record the changes made via its memory. Faders are used to obtain this
2. Why might the faders have to be moved during the mix?
To obtain the required levels between different instruments, voices and effects.
3. What aspects of mixing would normally be automated on an analogue console?
Channel muting, Eq and faders.
4. Comment on VCA vs. Moving Fader automation.
On Voltage Controlled Amplifier automation there is no audio signal passing through the fader. With Moving fader automation, signal is linked directly to the fader controls.
5. Describe write/update/read.
Write/update/read are modes used for recording the automation data. Update mode is used for modifications made. During the automated mix down process the data is read.
6. How does an automated mix session start?
By positioning the fader settings appropriately.
7. How would a section of automation data be re-recorded?
By using update mode, it would then restore what was pre-recorded, enabling the necessary changes to be made.
8. How are automation 'punch-ins' blended smoothly with existing data?
By using cross fades.
9. How could a complex series of moves be increased in level by say 3dB?
Incorporate the affected faders into one master fader (fader grouping). And then increase the group 3dB.
10. Describe fader grouping.
One fader is initiated as being group master. Whatever is done with the master fader will be done to the slave faders.
11. How could EQ, for instance, be automated using an analogue mixing console?
Adjust EQ in playback and enable write mode (write/read/update).
12. How would EQ be automated using a digital mixing console?
As above, adjust EQ in playback and enable write mode
13. What is 'recall'?
Recall is restoring settings that have previously been stored in the memory.
14. What advantages does a digital console have over an analogue console regarding recall?
Digital consoles offer memory to store various settings, e.g. EQ, dynamics and effects parameters to scenes or snapshots. These can be read back when needed
15. Does a compressor act upon loud signals or quiet signals? What does it do to the signals upon which it acts?
A compressor acts on loud signals. It reduces gain on signals exceeding the threshold, giving you a much more controlled sound.
18. What is the function of 'make up gain'?
To restore the level lost in the compression process.
19. How is a compressor usually connected to a mixing console to compress a single signal?
The input of the compressor is fed from the channel insert send, output is sent back to the channel insert return.
20. How is a compressor connected to a mixing console to compress the entire mix?
As above, except that the output channel insert points are used.
21. Explain 'ratio', in the context of compression.
Ratio determines the amount of compression once the threshold has been exceeded. For any gain of ratio dB in the input signal, the output signal from the compressor will have only one dB gain. So, ratio of 3:1 means 3 dB input gain gives 1 dB in output.
22. Describe the difference between hard knee and soft knee.
Hard knee means the signals will have full amount of compression once they pass the threshold level. Soft knee implies the gain reduction occur gradually, with signals closer to the threshold level being less compressed.
23. What are 'breathing' and 'pumping'?
Breathing/pumping is when the compressor’s release time is too short so that the increase in noise level will be audible.
24. What happens if the release time is too long?
”Breathing and pumping” The result would be constant gain reduction, which in fact could be achieved by lowering the fader.
25. What does it mean if the gain reduction meter is showing frequent changes?
The compressor is working effectively.
26. Describe the effect of compression on noise level.
Compression brings the peak levels down. Make up gain is applied to raise the overall level so that peaks are high again in the output.
27. Describe the function of the stereo link switch.
Stereo link switch is used to make compression in both channels behave in the same manner.
28. What is the side chain input?
Side chain input is an input to the compressor's driving circuitry. This is used for making the gain of the signal reliant on the level of another signal that’s applied to the side chain input.
29. Describe a typical use of the side chain input.
Recording voice-over to the musical track: a compressor would be inserted into the music channel insert point. The voice signal is taken from an auxiliary send and fed to the compressor's side chain input. It makes level of the music track dependent on presence of signal in the vocal track.
De-essing: the vocal part is sent simultaneously to two channels, one with a compressor attached to the channel insert point. The other channel is applied EQ boost on high 'essing' frequencies and sent through auxiliary send to the side chain input of the compressor. This way the vocals will be reduced in gain every time there are strong high frequencies present.
30. Is a noise gate usually effective on a mixed stereo signal?
Not Usually. There isn't much noticeable noise on a mixed stereo signal.
31. Is a noise gate effective on a signal where the instrument plays all the time?
No. If the instrument is playing all the time, there is no use for a noise gate.
32. Is a noise gate effective on a single noisy signal where there gaps in the playing?
Yes. A noise gate is meant to eliminate the background noise during these gaps where the instrument is not playing.
33. Why is it often considered beneficial to gate some or all of the mics on a drum kit (except the overheads)?
This is to minimize spill between drum microphones. By gating, you can make sure that the only time sound from each microphone is recorded is when the particular instrument that microphone is meant for is played.
34. How many gates are often used in live sound: none, a few or many?
Depending on how many instruments are being played, you can use as many gates as you like to minimise spill.
35. How is the noise gate connected to the mixing console?
Through an insert point on the channel you want the noise gate to affect.
36. What is the function of the Threshold control?
Any signal above the threshold level will be let through the gate, while signal below the threshold level is reduced.
37. What is the function of the Range control?
Range controls how much the signal below the threshold will be reduced.
38. Comment on the Attack, Hold and Release (Decay) controls.
The attack and release are set to control shape and sounds as it comes and goes away. The hold control has pre-programmed time, it comes, it plays, these are very useful.
39. What would happen if a stereo signal was gated, but the stereo link function was not selected?
When stereo link is selected, both channels are forced to open and close at different times.
40. Why are side-chain filters beneficial?
They enable you to send out signal to be processed, or open and close when required.
41. Comment on the use of an external key to improve the reliability of gating.
It lets that gate work at all times by selecting frequencies that permit the gate to open in all situations.
42. What is an expander?
Same as a noise gate, but it stays on all the time, and changes the dynamic range.
43. Why are compressors and gates often used together?
Because the overall effect on the music is smoother and all the levels are equal.
44. Comment on envelope shaping using a noise gate.
This is used to create different effects and sounds. First send it to the side chain to alter the frequency, and send it back, the overall effect, a whole new sound.
45. Comment on gated reverb.
Its effect is to give the reverb an abrupt cut off.
Kurt53 |
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Sat Oct 02, 2004 9:00 am |
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Rico1210
Joined: 03 Aug 2004
Posts: 39
Location: Newcastle, UK |
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Hi, here are my answers to Equipment 1, once again very interesting.
'Sound and Recording' textbook was a big help this week, especially for the automation questions.
1. What is the function of mixing desk automation?
Mixing desk automation is a means of storing fader positions to be used at a later point during a mix. Automation assists the engineer in mixdown when the number of faders that need to be handled at once becomes too great for one person. This allows the engineer to concentrate on specific areas of the mix during each pass.
2. Why might the faders have to be moved during the mix?
Faders would usually have to be moved during a mix as there are always sections where one track would need to be louder than another. For instance, the start of a song might have a very loud section that is a solo instrument, when other instruments or vocals are added the levels would need to adjusted to create a balance. Sounds are brought down to enable other sounds to be added.
3. What aspects of mixing would normally be automated on an analogue console?
Fader positioning, muting and the master stereo output would usually be automated on analogue console.
4. Comment on VCA vs. Moving Fader automation.
VCAs (voltage controlled amplifiers) control the levels of a group of faders without changing their levels in relation to each other. VCAs memorise the position of the faders and use the data to control the gain. Moving Fader automation does the same but actually physically moves the faders via a motor. The disadvantage of a VCA is that the fader position may not always correspond to the gain of the channel, but the advantage is that the change in gain is instant.
5. Describe write/update/read.
These terms are used to describe common operational modes of voltage controlled amplifier (VCA) automation. Write corresponds directly to the fader position and is used to record the automation. Read is controlled by data used from a previously stored mix and cannot be changed during playback. Update is controlled by a combination of previously stored data and current fader position, this is used to edit parts of the automation.
6. How does an automated mix session start?
An automated mixing session would start with a first pass of the mix with the faders set to write mode. This stores the absolute fader positions.
7. How would a section of automation data be re-recorded?
A section of automation would be re-recorded using the write mode of the console during playback, unless changes are needed, then the update mode would be used.
8. How are automation 'punch-ins' blended smoothly with existing data?
Punch-ins use two tracks of multitrack recording, therefore automation 'punch-ins' are blended smoothly with existing data by using crossfaders.
9. How could a complex series of moves be increased in level by say 3dB?
A series of fader movements could be increased by 3dB using the Update mode. In this mode the system assumes that the starting position is a point of unity gain, therefore it adds any changes made to the previously stored data. If a fader is increased by 3dB in update mode, the overall level of the passage is increased by 3dB i.e. all fader movements.
10. Describe fader grouping.
Often a number of faders can be moved up or down together. To reduce the number of faders an engineer is required to handle, these faders can be grouped together so that one fader controls them. The faders do not have to be at the same level and can be adjusted individually.
11. How could EQ, for instance, be automated using an analogue mixing console?
EQ automation on an analogue console would have to be adjusted manually during the mix, with write mode selected.
12. How would EQ be automated using a digital mixing console?
EQ on a digital console could be automated using the write or update modes. EQ automation settings could be recalled.
I couldn't find much information on EQ automation, could anyone point me to a website 
13. What is 'recall'?
Recall allows the engineer to call back previously saved settings.
14. What advantages does a digital console have over an analogue console regarding recall?
Unlike analogue consoles, digital consoles can save automation settings for a variety of tasks including effects and EQ. A digital console will have a lot of memory to store settings.
15. Does a compressor act upon loud signals or quiet signals? What does it do to the signals upon which it acts?
A compressor acts upon loud signals. It does this by reducing the level of the loud sections This reduces dynamic range, or reduces the difference in level between loud parts and quiet parts
18. What is the function of 'make up gain'?
Make up gain restores the level lost in the compression process. Compressors work by bringing down the loud parts, therefore the level of the output would be lower. Gain make up is applied to bring the output level back up to the previous level. The sections of the input signal that were quiet will now be louder.
19. How is a compressor usually connected to a mixing console to compress a single signal?
To compress a single signal, the input signal is routed to the compressor. The output from the compressor is then routed to the mixer. This setup prevents the signal from being affected by any of the console controls.
20. How is a compressor connected to a mixing console to compress the entire mix?
To compress the entire mix, the insert point of the main stereo output is routed to the compressor. Alternatively, the compressor can be connected to the group insert point of the console.
21. Explain 'ratio', in the context of compression.
In terms of compression, Ratio is the strength of compression above the threshold level. The higher the ratio, the greater the effect. If the ratio is set at 2:1, it means that when the signal is above the threshold level, if the input signal rises by 2 dB, the output signal rises by 1 dB. Compression ratios above 20:1 are no longer known as compression. Above this point it is known as 'limiting'
22. Describe the difference between hard knee and soft knee.
A 'knee' is the point where the slope of the compressor curve changes. This is variable between hard and soft. With a soft knee, signals which only just exceed the threshold level are compressed at a low ratio, the ratio increases the higher the signal. This creates a small curve. A hard knee is said to be normal, as it compresses at a constant ratio.
23. What are 'breathing' and 'pumping'?
'Breathing' and 'pumping' are unpleasant effects created when the noise level goes either up or down as the signal is doing the same. Basically, it is background noise.
24. What happens if the release time is too long?
The release time determines the rate at which the gain will increase. If this is set too long, the gain will stay at a low level only increasing gradually. Therefore it won't be compressed, rather reduced in level.
25. What does it mean if the gain reduction meter is showing frequent changes?
The gain reduction meter shows how much compression is going on. If the gain reduction meter is frequently changing, this means that there is active compression. The faster the meter goes up and down, the more compression is working. If the meter is steady, there is little compression taking place.
26. Describe the effect of compression on noise level.
Compression increases the noise level. This is because the peaks of the signal are brought down in level, bringing them closer to the noise floor. The make-up gain is applied bringing the signal level back up, raising the noise floor at the same time. This will always happen when compression is applied to noise.
27. Describe the function of the stereo link switch.
The stereo link switch is used when applying a twin channel gate to a stereo signal. When the switch is on, the channels are forced to open or close at the same time. When the switch is off for a stereo signal, the channels will open at slightly different times. This will make the signal sound terrible, apparently. I wouldn't know!
28. What is the side chain input?
The side chain input is an additional input featured on compressors. It allows the signal to be controlled by the dynamics of another signal.
29. Describe a typical use of the side chain input.
A typical use of the side chain input is 'De-essing'. De-essing is a compression technique used to reduce sibilants (s sounds) in a vocal. The sibilants are selectively removed by compressing only when there is an excessive level of high frequencies.
30. Is a noise gate usually effective on a mixed stereo signal?
A noise gate can only process one unmixed signal. It would not be effective on a mixed stereo signal as there would be no gaps in the signal that required the noise reduced.
31. Is a noise gate effective on a signal where the instrument plays all the time?
A noise gate is not effective when an instrument is constantly played, as the instrument itself will drown out any noise.
32. Is a noise gate effective on a single noisy signal where there gaps in the playing?
A noise gate works by closing or almost closing off the signal when there are gaps in the playing. It detects when the signal is low (intrument not being played) and blocks it off, therefore reducing the noise.
33. Why is it often considered beneficial to gate some or all of the mics on a drum kit (except the overheads)?
A drum kit is set up with a microphone on each drum and on the hihat. It is inevitable that to a certain extent spill will occur from the other parts of the kit, therefore it is beneficial to gate the microphones so that they are only open when that piece of equipment is being played. The overheads are there to record the overall sound of the kit, therefore this does not apply.
34. How many gates are often used in live sound: none, a few or many?
In a live performance virtually all microphones of the entire band would be gated.
35. How is the noise gate connected to the mixing console?
The noise gate is connected to the mixer via the channel insert point as it can only process one unmixed signal.
36. What is the function of the Threshold control?
The function of the threshold control is to set the level at which the gate will open or close. When the signal is above the threshold it will be open. When it is below the threshold it will be closed. When threshold is set at the minimum, the signal will always be above the threshold whether this is the instument or noise. When the threshold is set at the maximum, the signal will not be heard. A balance must be struck between open and closed to enable the signal to be heard, and the noise reduced.
37. What is the function of the Range control?
The function of the range control is to set the degree of attenuation when the gate is closed. The gating of a signal should not be heard throughout a mix. It is usual for the range control to be set at to the maximum but if the opening and closing of the gate is noticeable, then the range control should be set to achieve the best compromise.
38. Comment on the Attack, Hold and Release (Decay) controls.
The attack and release (decay) controls are used to make the transition from signal to silence (and back again) as smooth as possible. It shapes the envelope of the sound without letting noise get through or without cutting off any of the signal. The hold control sets a time period during which the gate will remain fully open, even though the signal has just dropped below the threshold. If the hold time is zero the gate will open and close rapidly when it crosses the threshold, this causes a 'jitter'. The hold control should be set to the point that causes the 'jitter' to cease.
39. What would happen if a stereo signal was gated, but the stereo link function was not selected?
The stereo link function is used when applying a twin channel gate to a stereo signal. When the sereo link is on, it forces both channels to open or close together. If the stereo link is off the channels will open or close at different times.
40. Why are side-chain filters beneficial?
Side-chain filters are used to control the behaviour of the processed signal. They can be used on microphones that are very close together to stop one signal from opening the gate of the other. This is very useful on a drum kit, where the hihat and the snare are very close together. High or low frequencies can be filtered out using the side-chain which enables the gates to differentiate between the two instruments.
41. Comment on the use of an external key to improve the reliability of gating.
An external key can be used when the gate is not functioning correctly even after using the side-chain filter. An external key is set up using a contact mic on the instrument which is fed via a preamp to the external key input of the gate. This signal will trigger the gate without almost no external sound, aswell as opening the gate slightly earlier than a regular microphone.
42. What is an expander?
An expander works much like a gate. Whereas a gate is either on or off, an expander increases the dynamic range when the signal is below the threshold. This makes the signal get quieter rather than just switching off. There is no effect when the signal is above the threshold. When the signal is above the threshold, there is no change.
43. Why are compressors and gates often used together?
Compressors and gates are often used together as compression increases the level of noise. This is because the peaks of the signal are brought down in level, bringing them closer to the noise floor. The make-up gain is applied bringing the signal level back up, raising the noise floor at the same time. Therefore a noise gate is applied to reduce the excess noise level. Compressors and gates can be connected with either one coming first according to an engineers preference.
44. Comment on envelope shaping using a noise gate.
A noise gate is not just a problem solver, it can also be used to create effects using envelope shaping. A constant signal can be fed through the gate which is then altered by an envelope to create a rhythm. This can be achieved using an external key signal to synchronize the input. An example could be chords played on an electric guitar, which are then synchronized to the drums fed through the external key.
45. Comment on gated reverb.
Gated reverb is a technique that was widely used in the 1980's. It works by sending some of the input signal to a reverb unit via an auxilary send, this is then routed to a channel where a noise gate is connected. The insert send of the original signal is then connected to the external key input of the gate. Hold and release controls are set to achieve long hold and short release, so that the reverb extends beyond the original signal, but then dies away suddenly. This is gated reverb. |
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Sun Oct 03, 2004 8:19 am |
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seanm
Joined: 06 Sep 2004
Posts: 20
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hi chris
please find my answers below, can you suggest an supplementary sources on mixer automation?
Week 4 - Equipment 1
1. What is the function of mixing desk automation?
Mixing desk automation enables the mixer setting for every channel to be stored, altered and recalled very quickly. Engineers and producers know how and when any mixer settings need to be changed during a mix but the physical dexterity and memory required can simply be beyond human capabilities. Such automation saves a lot of time enabling different mixes to be stored and recalled at will. It also enables the re-setting of the mixer prior to a new session instantly.
2. Why might the faders have to be moved during the mix?
Faders might be moved to increase the vocal level during chorus’s or boost a instrument during a solo section. Instruments might be faded in or out at certain points.
3. What aspects of mixing would normally be automated on an analogue console?
Analogue console automation ranges from none whatsoever to only being able to automate volume fader positions and level related switching functions, to being able to store and recall all dynamic functions (volume, pan, eq and sends).
4. Comment on VCA vs. Moving Fader automation.
In an analogue console the positions and moves of the various dynamic controls are converted into a DC voltage that can be converted into digital data. With VCA (voltage Controlled Amplifier) automation this voltage (equal to the parameters setting) is used to vary the gain of an audio signal. The automation system translates the voltage into digital data and on playback converts the data back into an equivalent voltage level, which directly controls the parameter level.
In moving fader automation, a fader will have two separate control paths. One to pass the audio signal and one to pass a DC voltage. Moving the fader changes the control voltage (again converted to digital data). On playback the control voltage is fed to a DC server motor in the fader which causes the fader to move to the correct position.
In mover fader automation the position of the fader reflects it’s actual volume at all times. Moving fader automation often employs touch sensitive faders, making updating of fader moves easier. Such faders are always in the read mode so any alterations are made and stored simply by moving the fader.
The switching automation employed in the moving fader type is easier to encode and decode as buttons have an off/on state that can be easily converted to digital using a simple and reliable silent transistor switching network.
5. Describe write/update/read.
During the write mode the system begins the process of recording all mix moves, live and in one pass or on each channel or groups of channels (to build up a mix in sections). On completion of each pass or passes the information can be written into the systems memory.
If parts of the mix automation were not satisfactory, for instance the overall level of one or more tracks was too high, it is possible to update these elements using the update mode. This is done without affecting any of the previously recorded settings.
When in read mode the mix plays back using all the automation settings stored.
6. How does an automated mix session start?
Before any attempt at automation set up a mix with a balance that seems as close as is required, along with panning, eq the main effects you intend to use. Only then place the required channel or channels in the write mode.
7. How would a section of automation data be re-recorded?
Using either the update mode or the write mode on the required channels.
8. How are automation 'punch-ins' blended smoothly with existing data?
High end consoles allow for more intricate editing and merging of automation information.
9. How could a complex series of moves be increased in level by say 3dB?
By grouping the appropriate channels and increasing the group fader by 3dB.
10. Describe fader grouping.
Channels can be grouped together allowing the one channel’s fader to control the volume of those selected. Grouping in this instance still allows the selected channel controls to remain independent.
11. How could EQ, for instance, be automated using an analogue mixing console?
With an analogue console EQ would be automated by converting changes in EQ settings into a DC voltage that is then converted into digital data. In an analogue console this can be done in two different ways depending on the model;
VCA where a voltage controlled amplifier is used to control the DC voltage transmitted by the alterations in EQ settings. On playback the digital data is converted back into a DC voltage and directly controls the EQ settings.
DCA where a Digitally controlled amplifier is used to convert the DC voltage into digital data. On playback co conversion is required as the signal has remained in the digital domain throughout and can be understood by the EQ settings directly.
12. How would EQ be automated using a digital mixing console?
With a digital console EQ automation can be achieved by either a VCA (as above) or via a digital controller. In this instance EQ parameters output their control settings in digital form. This information is understood by the console directly and is simply read by the consoles automation system.
13. What is 'recall'?
Automation mixes and parts of mixes can be stored for various purposes. Recall is the function which allows previous automation sessions (complete mixes or parts of mixes) to be reloaded into the console.
14. What advantages does a digital console have over an analogue console regarding recall?
Th ability to store and recall instantly a large number of different mixes with all their automation settings.
15. Does a compressor act upon loud signals or quiet signals? What does it do to the signals upon which it acts?
A compressor acts on the whole signal or in the case of multi-band compression a user-determined frequency range of the signal. Whether a compressor acts upon loud signals or quiet signals does depend on the reason it is being used. For instance it can be used to thicken up a signal in which case it’s likely that bringing up the level of the quieter sounds is part of the desired effect.
Compressors are designed to reduce the dynamic range of a signal or recording, they achieve this by reducing the level of signals which exceed a user-determined level. However most compressors include an output level control (make up gain) which allows any gain lost by compression to be restored (or made up) to bring signal peaks back to where they were before compression was applied. If enough make up gain is applied this will raise the gain of the whole signal including quiet signals.
18. What is the function of 'make up gain'?
Most compressors include an output level control (make up gain) which allows any gain lost by compression to be restored (or made up) to bring signal peaks back to where they were before compression was applied.
19. How is a compressor usually connected to a mixing console to compress a single signal?
Compressors are patched into channel insert points or between a sound source (e.g. bass guitar) and a line in.
20. How is a compressor connected to a mixing console to compress the entire mix?
In this instance the compressor will usually be patched into the desk's main stereo buss insert points. Occasionally a compressor might be patched into the aux send of the master stereo outputs if a mix of the compressed and uncompressed signal is desired.
21. Explain 'ratio', in the context of compression.
The ratio determines the severity of gain reduction applied to the signal once it reaches the threshold level. The higher this ratio the more gain reduction is applied to the signal and the stronger the compression effect. If the ratio is high enough it can prevent the signal ever getting above the threshold set. This however is technically “limiting”. Ratio is the number of dB by which the input level needs to increase to cause a 1dB rise in the output level. For example if the ratio is set to 5:1 an input signal exceeding the threshold level by 5dB will be reduced in level so it only causes a 1dB increase in output level.
22. Describe the difference between hard knee and soft knee.
Hard Knee compression is that which is applied to an input signal as soon as it reaches the threshold set. Hard Knee compression as a result can make an obvious and audible impact on a signal. This side effect of hard knee compression is often used as a production device to make an instrument stand out in the mix.
With Soft Knee compression on the other hand gain reduction actually begins a few dB before the threshold is reached but at a ratio lower than that set. As the signal approaches the threshold the ratio increases usually over about 10dB until it reaches the threshold when the user defined ratio takes over. Soft Knee compression is sometimes called invisible compression and is used when the desire is simply to keep the signal under control dynamically.
23. What are 'breathing' and 'pumping'?
If the release time is set too short the compressor gain recovers too quickly, resulting in a breathing or pumping effect due to the rapidly changing gain. Also when compression is making relatively large changes to an input signal (10dB or more) the noise floor also rises and falls correspondingly. When this noise floor rises and falls drastically it might become audible (e.g. between drum hits) this is often characterised by a “breathing” sound.
As most modern music contains a lot of energy at the bottom end of the frequency spectrum the kick drum and the bass are often dominant instruments in the mix. If compressor threshold is set below the peak level of the kick drum, each beat will cause the compressor to reduce the overall level and the result is a pumping effect.
24. What happens if the release time is too long?
When compression is making relatively large changes to an input signal (10dB or more) Pumping can occur when release time is too long. This results in the lower level of the signal becoming lost as the compressor slowly stops reducing gain. Effectively the make up gain of the compressor stops acting on the signal and leaves it back at its original level.
25. What does it mean if the gain reduction meter is showing frequent changes?
The dynamics of the original signal are being affected, this indicates that compression is taking place as the signals dynamics are being reduced.
26. Describe the effect of compression on noise level.
The noise level will be compressed along with the rest of the signal. If the make up gain is set so the maximum levels of the uncompressed signal and the compressed signal are the same then for every dB of compression applied the signal to noise ratio is worsened by 1dB. This is because the quieter parts of the original signal (where noise is probably more apparent), plus any noise it contains will be raised in level.
27. Describe the function of the stereo link switch.
The stereo link switch ensures that both channels are compressed in the same way, regardless of whether the biggest signal peaks occur on the left or right channel. Linking combines the side chain signals so that the compressor responds to an average of both channel levels. For proper stereo operation each channel still needs a separate envelope follower as part of the side chain. Simply combining the left and right channels can cause phase cancellations, which can result in inadequate amounts of gain reduction being applied to some sounds.
28. What is the side chain input?
The side chain is the circuitry that monitors the level of the signal coming in to the compressor. The side chain input allows other processors to be connected to the compressors side chain path, or to allow the side chain to be fed from a different source altogether.
29. Describe a typical use of the side chain input.
One typical use is for de-essing a vocal. A graphic or parametric equaliser is patched in to the side chain insert point (input) and tuned to boost the sibilant frequencies of the vocal track. The signal is then returned to the compressor. This will make the compressor more sensitive to these frequencies.
30. Is a noise gate usually effective on a mixed stereo signal?
Gates are most effective on signals containing gaps. These gaps being where any noise in the signal will be most apparent. On the whole full mixes are unlikely to contain such gaps. All gating should really have been done much earlier in the recording process anyway. The only circumstances where a gate might be applied to a full mix is if the gate is being used as an effect or to clean up a noisy song start and ensure the mix fades into true silence at the end.
31. Is a noise gate effective on a signal where the instrument plays all the time?
No the gates threshold is designed to allow through only those sounds which are above its level (opposite to a compressor). With a very simple gate sounds below this threshold are silenced immediately they fall below the threshold level. A constant signal will be impossible to gate without causing the signal to stutter anyway a constant signal will be masking much of its inherent noise by its very nature.
32. Is a noise gate effective on a single noisy signal where there gaps in the playing?
Yes see above.
33. Why is it often considered beneficial to gate some or all of the mics on a drum kit (except the overheads)?
This is beneficial to minimise the spill from nearby instruments which are not struck at the same time. It could also be used to minimise phasing.
34. How many gates are often used in live sound: none, a few or many?
Many, gates are used live to eliminate spill on vocal mikes (during gaps in singing. Gates are used live to separate instruments in the drum kit to assist in achieving a more controllable drum mix. Gates are also used live to eliminate unwanted noise from electric guitars and basses when they’re not being played.
35. How is the noise gate connected to the mixing console?
A noise gate is normally patched into a mixer via an insert point, or connected in-line between one piece of equipment and another. Normally if gateing is to be applied to a signal it will be applied “pre fader” because it is not necessary to mix a wet and dry signal as this will cancel out the action of the gate.
36. What is the function of the Threshold control?
The threshold is set by the user. It is the level below which the signal is muted. In a simple gate, without attack, hold or release functions it is simply on (mute signal) or off (allow signal through).
37. What is the function of the Range control?
The range control attenuates a signal, which is below the threshold rather than muting it. For instance if a signal contains room ambience which is desired but too loud, the range control can be set to attenuate the signal and allow it to pass even when the gate is closed, but at a lower level.
38. Comment on the Attack, Hold and Release Decay) controls.
Attack, controls how quickly the gate opens fully once the input signal reaches the threshold. If the gate opens too quickly low frequency sounds might distort due to the gate switching on part way through a cycle. This can produce an audible “click”. Slowing the attack time down can overcome this.
Release, controls how quickly the gate is closed again. Instead of switching off immediately when the signal falls below the threshold and chopping off low level sounds the release control can be set to allow the sound to fade over a period of time.
Hold, controls how long the gate stays open before entering the release phase. User controlled it holds the gate open after the signal has fallen below the threshold level for a selected period before the release phase is invoked. It is used to stop the gate from “chattering”. Chattering occurs if a gate switches on and off very quickly in the presence of a signal that has an undulating level, such as a decaying guitar chord with a tremolo effect.
39. What would happen if a stereo signal was gated, but the stereo link function was not selected?
The stereo link switch forces both channels of the gate to open and close at the same time. If the stereo link switch is not selected the two channels will be gated separately opening and closing being dictated by their own gates causing an inbalance in the stereo spread.
40. Why are side-chain filters beneficial?
Side chain filters are usually a pair of variable frequency high and low pass filters. These filters do not affect the sound of the output signal in any way. They only affect the gate’s triggering circuitry. As they are built in there is no need to patch in an external equaliser.
41. Comment on the use of an external key to improve the reliability of gating.
Inserting an equaliser into the external key input can improve the gates sensitivity to some frequencies rather than others. This can improve the reliability of the gate in some circumstances. For instance when gating a snare drum containing enough spill from the bass drum to occasionally open the gate (at unwanted times), filtering out lower frequencies from the side chain input signal can make the gate less sensitive to the spill from the bass drum.
42. What is an expander?
An expander is similar to a gate. However unlike a gate (with range set to maximum) it does not mute/silence signals that fall below it’s threshold instead it applies gain reduction to these parts of the signal. The amount of gain reduction depends on the ratio setting of the expander. For instance a 1:2 expander ratio means that for every decibel the input signal fell below the threshold, the output would fall 2dB.
With a low ratio setting expanders can be used to subtly increase the dynamic range of signals falling below the threshold. If the threshold level is set very high and the ratio low then the whole signal is expanded.
43. Why are compressors and gates often used together?
Gates are usually placed before compressors in the signal chain. This is so that as much unwanted material as possible is compressed. As compression will raise the overall volume of noise, spill etc.
44. Comment on envelope shaping using a noise gate.
A noise gate can be used to shape the envelope of a sound. For instance varying the attack time can soften the attack of a signal. The release time can be used to cut the end of a signal to tidy up a rhythm guitar signal. An external key input using a bass drum signal can be used to tighten up a bass guitar which is slightly off the beat.
45. Comment on gated reverb.
Where possible any reverb should be added after gating as controlling the envelope of a signal containing reverb can be difficult if it is intended to sound natural. This is because the added reverb is easily chopped off resulting in an unnatural sounding reverb.
But gated reverb is also a common effect used particularly on drums. To achieve this sound the kit is close miked with ambient mikes positioned to pick up the ambience of the whole kit and natural reverb. The signal from the ambient mikes is often compressed (to keep the reverb effect as high as possible) and patched into the gate. The signal from the close mikes is fed into the gate’s side chain input. The gate is then set up using a hold time up to half a second and a very fast attack and release time. This produces a very hard gated reverb sound. |
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Mon Oct 04, 2004 7:10 am |
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