A constantly asked question is :
"How do I set the threshold, attack, hold and release controls on a compressor or noise gate?"
First lets get the names straight

*Theshold* is the level above which the dynamic device acts. Theoretically, signals below the threshold would be completely unaffected by a compressor and would be muted by a gate. Signals above the threshold would be squished by a compressor or let to flow unolested by a gate.

*Attack* is the time it takes between when the threshold is crossed and when the dynamic device takes full effect. For a compressor, this would be the time between when the compressor does nothing to your signal and when it exhibits its "squash" For a gate, this would be the time between when the gate lets all signal thru and the time when it mutes the output. The attack time is usually in the form of a fade rather than an abrupt event, though with a short enough attack it can be quite abrupt indeed.

*Hold* or *sustain* is the amount of time AFTER the attack time ends AND (VERY IMPORTANT HERE) after the signal has gone back BELOW the threshold that the compressor will squish or the gate will remain open BEFORE the *Release* time starts.

*Release* is the time AFTER the signal has gone back below the threshold and AFTER the *Hold* time is past that the compressor fully stops squishing ( thereby letting the signal thru unnaffected) or the noise gate fully mutes the output.

Now that we are SPOILED ROOTEN with our two track editors and DAW's compressor and gate setting is VERY much easier, at least technically. Lets say we need to determine settings for a gate on a snare.
Just find one good " representative " snare hit and zoom in.
Take a look at the initial attack of the snare. Note the level, 1 or 2 dB below this would be a good place to set your threshold, ASSUMING that your gate is set to read "PEAK" level and not "RMS". Now select and measure the initial attack length(time)wise. If you wanted to mellow out a snare hit you would set the attach a little on the slow side, perhaps even the entire length of the initial attack. In most cases however, youd want as short an attack time as possible. Even possibly the " predict" or "lookahead" feature found on some gates. This feature should work MUCH better on a PC than the treal world as the PC can look ahead, and already knows whats coming. But for some reason, this feature is always a little screwed up

Now zoom in and measure the part of the snare signal that is the " body " of the sound. This would be after the "Crack" of the initial attack, but usually before the fade out of the trap itself. Use this as your *Hold* time.

Now zoom in and measure the period after the body, but before that next god DAMN hi hat hit that is always bleeding into our snare tracks ! Use this time as the release. If that hat gets in there and gets suddenly cut off, it will sound goofy, so be careful here.

As an example lets say we have a snare drum. We want to gate the track and let only the snare thru. Say the threshold of a gate is set at -12dB, the attack is at 5 mS , the hold is set at 90 mS and the release is 100 mS.

As soon as a signal on that snare track exceeds -12dB the gate will start to open. 5 mS later the whole volume of the track is let thru. This particular snare has an initial attack of 25 mS then drops to the "body" at -8dB.

25mS After the inital attack the signal drops below the threshold and the Hold time kicks in. This lets the entire body of the snare thru, untouched, for 90mS.

After this 90mS the signal starts to fade out and after the release time of 100mS the signal is completely muted.