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Gain Structure (Gain Staging, all the same thing)
What is Gain Structure? Well Gain (don't get confused on this gain = trim, volume, etc.) structure is simply to volume that the signal has as it moves through the signal flow.
Yah? what about it...
Gain Structure is so important, in every sound application.
Improper gain structure can cause:
-Clipping
-Distorting
-Lack of headroom
-Destruction of Dynamic Range
What is headroom?
Headroom, in simplest terms, is the ability to turn a signal up with out clipping, or reaching the max volume capacity.
Headroom issues usually occur when all of the tracks in your session all dump into a master AUX track. All the track's output signal combined going into one track equals a lot of signal trying to go trough one track. Lets think of the road that all of the audio tracks take to get to the master fader. That road only has so much capacity (it's not unlimited guys), if you have all your track volumes at "-5 dB" (see section below), that main road to the Master track will be too full, we usually see a clip light because of this. THEREFORE the common practice and a way of "increasing headroom" is to turn the AUX track fader down. THIS IS SOOOOO NOT TRUE, a lot of "professionals" will try to tell you this... but it is not true. It doesn't work because 1. that fader controls how much the track is pushing out, if the meters are set to show the output volume (post-fader mode) the meters are showing the output. Sure when you pull the fader down the clipping stops on the output, but does that mean it's not still occurring on the input, nope and 2 that "road" still is full, no mater what you do on an AUX track. Having clipping on the input will cause distortion and loss of dynamic range.
Yah? what about it...
Gain Structure is so important, in every sound application.
Improper gain structure can cause:
-Clipping
-Distorting
-Lack of headroom
-Destruction of Dynamic Range
What is headroom?
Headroom, in simplest terms, is the ability to turn a signal up with out clipping, or reaching the max volume capacity.
Headroom issues usually occur when all of the tracks in your session all dump into a master AUX track. All the track's output signal combined going into one track equals a lot of signal trying to go trough one track. Lets think of the road that all of the audio tracks take to get to the master fader. That road only has so much capacity (it's not unlimited guys), if you have all your track volumes at "-5 dB" (see section below), that main road to the Master track will be too full, we usually see a clip light because of this. THEREFORE the common practice and a way of "increasing headroom" is to turn the AUX track fader down. THIS IS SOOOOO NOT TRUE, a lot of "professionals" will try to tell you this... but it is not true. It doesn't work because 1. that fader controls how much the track is pushing out, if the meters are set to show the output volume (post-fader mode) the meters are showing the output. Sure when you pull the fader down the clipping stops on the output, but does that mean it's not still occurring on the input, nope and 2 that "road" still is full, no mater what you do on an AUX track. Having clipping on the input will cause distortion and loss of dynamic range.
The best way to increase headroom is to pull all your track faders down BEFORE you start any mixing. The easiest way to do this is to activate the "ALL" group and drag down one fader which will turn-down all the faders at once.
The difference between AUX Tracks and Master Tracks.
There is one very important difference between these two tracks that is very commonly overlooked, if even known.
The volume fader on an AUX track controls the OUTPUT volume of the track, like mostly any other track,
On the Master Track, the volume fader controls the INPUT volume of the track.
*Keep this in mind when adding plug-ins to a master track, because lowering the fader volume will also decrease the input volume of the track, lowering the volume going into the plug-ins. So... will turning this input down increase headroom? Nope. The road is still full, no matter how much the Master track is letting in.
There is one very important difference between these two tracks that is very commonly overlooked, if even known.
The volume fader on an AUX track controls the OUTPUT volume of the track, like mostly any other track,
On the Master Track, the volume fader controls the INPUT volume of the track.
*Keep this in mind when adding plug-ins to a master track, because lowering the fader volume will also decrease the input volume of the track, lowering the volume going into the plug-ins. So... will turning this input down increase headroom? Nope. The road is still full, no matter how much the Master track is letting in.
The volume scale
This isn't usually covered, so I though I should cover it.
This isn't usually covered, so I though I should cover it.
On meters an VUs we usually see a scale to the side that starts at the top at "0" and goes down to maybe "-30" or "-40" (sometimes the "-" isn't there, but that's ok, we'll forgive avid for being lazy ;) ). This is commonly overlooked but is very important in Gain Structure and Headroom.
These numbers are measuring dB (decibels), so you would think the scale would start at "0" and go up, like normal scales, but this scale measures a bit differently. 1st thing to know is the universal threshold among audio devices known as max volume level, anything above this normally would be clipping. The volume scale measures how many Decibels away from the max volume the signal is. The "0" at the top represents 0 decibels till the max is reached, which really means your at the max. "-10" represents 10 decibels under max volume, as so fourth. Most analogue devices can go over the universal Max Volume, this is represented on the scale with a +. For example signal coming out of an analogue EQ can be "+10" decibels above clipping, but, of course can run at "-10" decibels and so fourth, it just has the special ability to go above. Most digital audio devices and power amplifiers still clip a
at "0" Decibles.
Volume controls also follow this scale, however they go over "0". For example, if a volume control is at "-40" it means it is removing 40 Decibels from the signal, if it is at "+5", it is adding 5 Decibels to the signal, if it as at "0" it is doing nothing. Don't get confused and think if a volume control is at "+5" that the signal also is at "+5". This is not the case, a volume control scale simply means that it is boosting the signal. For example if a signal that is at "-11" (11 Decibels below Max), if that signal ran through a volume control at "+5", the signal would be "-6" (6 Decibels below clipping) because it was 11 away, if you add 5 it is now 6 away.
At the bottom of both the volume controls and the volume meter scale, there is "(-)infinity", labeled by -∞ or -inf. This basically means no sound is coming through, or is allowed to come through.
These numbers are measuring dB (decibels), so you would think the scale would start at "0" and go up, like normal scales, but this scale measures a bit differently. 1st thing to know is the universal threshold among audio devices known as max volume level, anything above this normally would be clipping. The volume scale measures how many Decibels away from the max volume the signal is. The "0" at the top represents 0 decibels till the max is reached, which really means your at the max. "-10" represents 10 decibels under max volume, as so fourth. Most analogue devices can go over the universal Max Volume, this is represented on the scale with a +. For example signal coming out of an analogue EQ can be "+10" decibels above clipping, but, of course can run at "-10" decibels and so fourth, it just has the special ability to go above. Most digital audio devices and power amplifiers still clip a
at "0" Decibles.
Volume controls also follow this scale, however they go over "0". For example, if a volume control is at "-40" it means it is removing 40 Decibels from the signal, if it is at "+5", it is adding 5 Decibels to the signal, if it as at "0" it is doing nothing. Don't get confused and think if a volume control is at "+5" that the signal also is at "+5". This is not the case, a volume control scale simply means that it is boosting the signal. For example if a signal that is at "-11" (11 Decibels below Max), if that signal ran through a volume control at "+5", the signal would be "-6" (6 Decibels below clipping) because it was 11 away, if you add 5 it is now 6 away.
At the bottom of both the volume controls and the volume meter scale, there is "(-)infinity", labeled by -∞ or -inf. This basically means no sound is coming through, or is allowed to come through.
Setting Good gain structure
Gain Structure starts at the recording process. It is good to record signals somewhere between "-6" and "-10". PLEASE NOTE: Pro Tools meters can be showing 2 things: Pre fader and Post fader (changeable under the options menu). For recording you want pre-fader because that directly shows the volume level that is coming into Pro Tools. It is best to change it to post-fader after recording because that meter show the output of the channel, best for mixing.
When completed with mixing, turn all your faders down, so that the Master Track is showing a good level (around maybe "-6" or "-10"). Or if you mix instrument by instrument, don't make the first instrument at "-6" to "-10", because adding other instruments above this will make the signal louder and could possible cause clipping and a lock of headroom.
Lastly, make sure you have good Gain-Structure between your plug-ins. It is good to gain match between your plug-ins because that makes sure that they are only affecting the sound, not the volume level. This could be a problem because this could increase the volume of all the tracks, making what was "-6" on the output a bit too close to "0". Also when you are auditioning plug-ins "bypassing and enabling them to see their affects), you don't want to have one be louder, because louder usually is voted as better, so you want both signals to get a chance at the same volume. Try to leave the input alone (except on the 1st one if it is too loud, for the signal you decrease be sure to compensate on the fader), instead adjust the output of the plug-ins to compensate for added or subtracted volume.
In Pro Tools, don't worry about the signal being "too low"
Sure, in the analogue world the motto was: record as loud as you can- so the signal-to-noise ratio would be more towards signal (analogue circuitry can introduce hum and hiss into the sound).
In the digital world this is no longer an issue, because it's all just code- no circuitry to add hum or hiss.
When you record make sure that your are not initiating hum/hiss in the recording process, but after that you can have the levels as low as you want in Pro Tools because it's all just hum-less code!
When completed with mixing, turn all your faders down, so that the Master Track is showing a good level (around maybe "-6" or "-10"). Or if you mix instrument by instrument, don't make the first instrument at "-6" to "-10", because adding other instruments above this will make the signal louder and could possible cause clipping and a lock of headroom.
Lastly, make sure you have good Gain-Structure between your plug-ins. It is good to gain match between your plug-ins because that makes sure that they are only affecting the sound, not the volume level. This could be a problem because this could increase the volume of all the tracks, making what was "-6" on the output a bit too close to "0". Also when you are auditioning plug-ins "bypassing and enabling them to see their affects), you don't want to have one be louder, because louder usually is voted as better, so you want both signals to get a chance at the same volume. Try to leave the input alone (except on the 1st one if it is too loud, for the signal you decrease be sure to compensate on the fader), instead adjust the output of the plug-ins to compensate for added or subtracted volume.
In Pro Tools, don't worry about the signal being "too low"
Sure, in the analogue world the motto was: record as loud as you can- so the signal-to-noise ratio would be more towards signal (analogue circuitry can introduce hum and hiss into the sound).
In the digital world this is no longer an issue, because it's all just code- no circuitry to add hum or hiss.
When you record make sure that your are not initiating hum/hiss in the recording process, but after that you can have the levels as low as you want in Pro Tools because it's all just hum-less code!