The EQ and compressor sections of Focusrite's top‑flight ISA430 processor can be flexibly configured in the signal path. However, such flexible signal routing is rare, and many other recording channels have a fixed signal routing which might not suit some applications.
I'm writing because I would like to know what difference it makes patching EQ before a compressor as opposed to after it. If I patch it pre‑compressor, will the compressor reduce or exaggerate the effects of my EQ'ing?
J C Brock
Assistant Editor Mike Senior replies: This is a thorny problem. Both routings have their uses, and there's not really any hard‑and‑fast rule you can follow: you just have to use your ears. However, whenever I'm trying to decide which routing I need, I first try getting a compression sound I like, before using any EQ at all. If I manage to achieve the compression characteristics I'm after then I'll only EQ after the compressor.If I can't get the compression to sound right, then I'll try carefully EQ'ing before the compressor in order to get the compression sounding right, even if that means boosting a frequency before the compressor and cutting it again afterwards to retain some of the original tonal contour.
Here's an example which ought to help explain this. Let's say that I'm recording a guitar and I keep getting a strong low‑frequency resonance picked up by the mic. If I tried compressing it first without any EQ I'd probably find that the resonance wouldn't allow me to get the result I was after — the excessive low frequencies would hit the compressor too hard, causing the high frequencies to vary in level unnaturally. Therefore, I'd probably end up EQ'ing a little of the bass out before the compressor, in order to stop this happening.
The subtext of all this, though, is that I'm assuming that you agree with me that you don't like the sound of the compressor acting unnaturally in this case. If you happened to like the way the compression sounded, then you'd only want to EQ after the compressor, and then only if there were any further tonal shaping to do.
I find it helps to think that the purpose of EQ before a compressor is primarily to tailor the response of the compressor, whereas post‑compression EQ is for general tonal shaping and for helping things mix nicely. If you're wanting to EQ in order to help something cut through a mix then you should do it after any compression otherwise the action of the compressor from moment to moment will tend to undermine any cut or boost you apply.