Live sound: Fine-tuning channel EQ

I’ve just been unexpectedly covering sound duty for our two morning services, and took some time to really play with the EQ facilities offered by our new desk, particularly during the sermon.  Above is a picture of the EQ section for the radio-mic I was using, and it looks pretty extreme, huh?  Lots of huge cuts if the gain indicators (the red LED’s at the bottom) are anything to go by.

Now, if someone showed me their analogue desk and I saw a channel EQ with quite so much taken out as shown, I’d have taken them back on for more teaching about gain structure and microphone choice/placement among other things. On most analogue desks there’d be nothing left of the original signal. You’d end up with an EQ curve looking a bit like the yellow line shown here:

Extreme EQ, “standard” analogue desk style. Low shelf frequency is around an octave higher here than most analogue desk EQ, and high shelf around two octaves lower. The yellow line goes off the lower scale, it’s so extreme.  You’d need to add at least 12dB of gain to the fader or pre-amp to get the original signal energy level back, assuming you don’t distort the pre-amp or other areas of the desk!

On our iLive system, things are a little different, as shown in the image below. We now have the ability to notch out problem frequencies with much more precision, mostly because we now have the ability to create very narrow (in terms of the frequency range affected) EQ filters. For live sound, this means we can make deep, narrow cuts to problem (resonant) frequencies and leave the rest of the signal alone.  This means that the problem frequency bands can still be attenuated, but without losing anywhere near as much of the overall signal energy.

This allows us to run with less gain at the pre-amp stage, which makes for less background noise and less chance of distorting any audio stage in the desk, whether digital or analogue. Because I’m not having to boost the pre-amp gain, I’m not changing the gain structure in any way, which is a Good Thing™ for too many reasons to detail here.  Because I’m not boosting either overall levels or particular frequency bands, I’m not introducing new potential feedback points to my mix – again a Good Thing™.

Of course, this benefit isn’t unique to the iLive system, but I used it to illustrate the problem as a) I have one and b) I happen to like how it sounds!

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