Brief Summary

It makes no difference whether the EQ is placed before or after the reverb when setting up the Abbey Road Reverb Trick. When comparing pre and post EQ prints, unmodulated reverbs null to zero.

Going Deeper

The Abbey Road Reverb Trick is up there with the Pultec Bottom End Trick or the 1176 All Buttons In Trick for super-clickable, internet friendly audio content. It’s simple, quick, and it refers to something famous in the name. If you’re not familiar with it, it’s a technique for cleaning up reverbs by using filters. Specifically it involves putting a high and a low pass filter before a reverb, sometimes with an upper midrange cut as well. Some people present the specifics as non-negotiable - the most common settings are a 12dB HPF and LPF at 600Hz and 10kHz respectively, with a -3dB cut at 2kHz. However, one thing which is always presented as mandatory, and forms the crux of this ‘trick’ is that the filters must be placed before the reverb.

The thinking here is that by filtering the potential mud, splash and harshness out of the audio before it reaches the reverb, those frequencies won’t excite the reverb in the same way, resulting in a cleaner result, also allowing more reverb to be used if desired without the wetness cluttering the mix. This makes a lot of sense. After all, if less energy is fed into the reverb at specific frequencies, it will affect the decay of the reverb. And if for example a build up of low frequency energy in the reverb is causing congestion in the lower midrange, then filtering the input will give different and cleaner results than filtering the output of the reverb will. Sounds plausible to me.

Pre VS Post EQ Sounds Plausible But Isn’t True

The only thing is, as the video below demonstrates, it actually makes no difference whether the filters are before or after the reverb. I was surprised by this, as the pre-reverb filter approach sounded perfectly plausible to me and I’d accepted it without question for years. But if you null test the results running your reverb with EQ both before and after the reverb, with one important exception, it makes no difference. And regardless of what one expects to be right, if two signals null, they are the same.

Modulated Reverbs Don’t Null

The exception I refer to is in the case of modulated reverbs. Many classic digital reverbs such as the Bricasti or many Lexicon algorithms use modulation as a way to avoid the unpleasant side effects of ringing and resonance created by trying to get too much out of too few resources in those early hardware reverbs. Modulated reverbs don’t null against themselves because the change over time the modulation introduces is different in each pass, regardless of where any additional filters might be placed.

The reasons why it is so commonly held that the EQ should be before the reverb might be based in the specifics of how the EQ was implemented in hardware at Abbey Road, perhaps it was convenient to EQ before the reverb but I’m speculating here. The thing which is certain is that when comparing unmodulated reverbs with EQ before and after the reverb they null to silence.

This doesn’t make the Abbey Road reverb trick any less useful. It’s a good technique and sounds great. Just don’t worry about where you place the EQ.