Live Vocal Compression and Drum Gating

How to make them work worth a darn.

Updated 03/09/2013


(Please note that the terms sidechain, detector, and key are used herein pretty much interchangeably.  If you are not familiar with these terms, read a few manuals or white pages and youíll be in the know.)

Vocal Compression
: It just doesnít get the job done.  The wimpy low notes are compressed as much as the loud screechy high ones.  Whatís the deal?

The main problem is the mic.  Unlike in the studio, a live vocal mic needs to be worked very close, lest the band end up as loud in the mic as the singer.  Nearly all directional mics have a ridiculous amount of low-mid boost when used up close.   Here's the response of a popular model:

Proximity.jpg (29400 bytes)

We can of course correct this sound-wise with the channel EQ, but the problem is still there so far as the compressor is concerned: The compressorís place in the signal path is usually right after the mic preamp.  The compressor (or more correctly its detector circuit) is thus presented with a signal that has a frequency balance thatís far from what went into the mic.  As such, the hugely boosted low-mids are what first reach the level thatís required to activate the compressor (via its detector).  Those screechy highs -  which are often sung back from the mic and are thus have less of the low-mid boost - donít have the amplitude needed to do much more than Ďtickleí the compressor.  No amount of fiddling will give you the smooth, even vocals of a really good recording.  But there are ways to get around this, sometimes to a great degree.

My favorite solution is a multi-band compressor, such as the (discontinued) T.C. Triple C or the Waves C4 plug-in.  Thereís also a multiband compressor available in some consoles.  Some are good, some are a nuisance to use on the fly (Yamaha LS9).  These break the frequency spectrum into a number of bands that can be compressed individually as desired.

A solution that can work with your existing compressor (if  you are lucky) is sidechain (aka key or detector) EQ.  By inserting an equalizer into the detector circuit (some compressors, such as the Rane C4, have this EQ built in), you can compensate for the micís big low-mid boost, and if desired make it more sensitive to those screechy high notes.  It does not work as well as multiband (the compressor still turns the entire spectrum down equally - you just have control over the frequency spectrum that Ďtellsí the compressor to turn down), but it can give a much more satisfying result.

If you have a spare subgroup, another solution is to assign the channel in question to its own group, and perform the compression in the group.  When doing so, the compressor will be in the signal chain after the channel EQ (in which you have used a big EQ cut to compensate for the micís proximity boost), and thus the detector will Ďhearí a signal that has a much more natural frequency balance.  If you have EQ in the subgroup, this would be the place to make any upper-mid or high frequency cuts (hopefully this EQ is after the compressor, and as such it wonít affect the compressorís actions).


Gates: They just donít work worth a crap.  By the time you get the floor tomís gate set such that it does not open every time the drummer strikes (bashes the hell out of) the snare, the gate opens only when the floor is hit harder than usual (a friend and I both find the gates in the StudioLive16 to be particularly disappointing).  The micís proximity effect isnít much help in this regard, as the center of the boost is an octave above the drumís strongest frequency. 

Again, sidechain EQ is the ticket.  Some gates (Rane G4, Studiolive24, Yamaha LS9) have it.  If  yours does not, it hopefully has a sidechain insert.  The goal is (more or less) to tailor the response such that the drumís loudest frequency area is boosted, and the rest is cut.  This will make the gateís detector more sensitive to the drum, and less sensitive to the rest of the racket that the mic is picking up.  If the gate has the EQ built in, there will likely be a Ďkey listení feature that allows you to hear the equalized detector signal, making tweaking of the EQ pretty easy.  If you are using an inserted EQ, temporarily patch the output of the EQ into an unused channel so you can listen to it.  Once you have it tweaked, connect it to the sidechain insert.

On some digital consoles, the detector (key) can be set to Ďhearí the signal of another channel.  If this signal is post EQ, you can wye the drum to an unused channel and use this channelís EQ has your sidechain EQ.

Now you can use the gate.  What for?  That depends on the genre, the drummer, and the tuning.  For jazz, you likely wonít use it Ė you may not even close mic most of the drums.  For blasto rock, you likely canít get the big tom sound you want because the drums drone on like a wounded cow.  Thatís where the gate comes in.  By adjusting the threshold, hold, and release, you get a reasonable amount of control over how much the drums ring.  This can be especially helpful if thereís a lot of sympathetic vibration of the heads due to a resonant stage, a big bass rig, or a drummer whoís so deaf that he wants the drums in his monitor(s).


 I wrote this in the wee hours, so if you find any goofs, let me know.