EQing in stereo

EQing in stereo

Put on a pair of headphones. Or make sure you’re positioned in the “sweet spot” of your speakers, so that you have a very clear stereo image. Then listen to these two versions of the same loop.

Version A:

 

Version B:

 

Which version do you prefer? There’s no right answer.

The only difference is that version B has this EQ on the master bus:

ProQ1

You don’t have to use FabFilter Pro-Q 2 for this. But in terms of workflow, it’s my favourite EQ.

Pro-Q can operate in two different channel modes: Left/Right or Mid/Side. In L/R mode, each filter can work on either L, R, or both. In M/S mode, each filter can work on either M, S, or both. You select the “Channel Mode” at the bottom, and the channel for each filter with the buttons next to the Q knob (the scissors point to which channel your filter is operating on):

ProQ2

Mid-Side processing is a very useful technique, and I’ll give a good example of this later in the post.

For now, I have 3 filters, and their settings are:

  • Left channel, 7027.4 Hz, Q: 1, +3 dB
  • Right channel, 7027.4 Hz, Q: 1, -3 dB
  • Right channel, 10541 Hz, Q: 1, +3 dB
  • Left channel, 10541 Hz, Q: 1, -3 dB

See the pattern? Everything I boost on the left channel, gets cut by exactly the same amount in the right channel. And vice versa.

Why do this?

There are lots of stereo widening techniques, including delays, chorus / phaser / flange, panning alternate takes, early reflections, reverb, binaural HRTFs, and a whole load of frequency-domain effects.

But here we’re not really trying to widen the stereo image, but more create a subtle sense of space and separation. (Although, 99% of this should come from our mix in the first place!)

Some people have theorised that the alleged sense of “3D-ness” that occurs when mixing on an analogue mixing console, or recording through lots of analogue gear, is due to the minor frequency response and phase response changes than happen due to imperfections and tolerances in all the devices, leading to a bigger difference in frequency response between the left and right channels. Personally, I have no idea to what extent this is true, as I grew up using computers for everything.

But it’s always fun to experiment.

What about mono compatibility?

So far I’ve been using Pro-Q in “Zero Latency” mode, which uses IIR filters. So technically, the EQ that I’ve applied here isn’t mono compatible. But in practice, it is. The difference when listening in mono is so marginal I almost can’t hear it. And if I’m really worried, I can always switch Pro-Q into “Linear Phase” mode.

Stereo EQ can work well on individual tracks too

Listen to the dry version of the loop again (Version A):

 

And then listen to this new version, Version C:

 

This time there’s nothing on the master bus. But I have applied another EQ, to just the hi hat track:

ProQ3

I’m not going to list out all the parameters, because you get the idea. As before, I’m using equal and opposite filters on the left and right channels.

The hi hats seem to occupy a different space. They’re a bit wider, but the point is that they have more of a shape to them.

There’s no need to restrict this technique to only the high frequencies. Just make sure you always check how your mix sounds in mono. And as always, use your ears. This is the kind of technique that you’ll want to use sparingly.

High frequency side boost

Finally, I’m going to show you a very common technique, using Pro-Q in Mid/Side mode. Again, here’s our Version A:

 

And here’s a new version, Version D:

 

Here’s what I have on the master bus:

ProQ4

It’s a high shelf boost to the side channel only. Usually I wouldn’t boost the side more than about 1 dB, but here I’m trying to make the difference more obvious, so I’ve boosted by a bit more.

For those not familiar with Mid/Side processing, there are lots of places online that explain it well. But as a summary, it’s exactly what it sounds like: the Mid is the centre / middle of the stereo image, and the Side is what’s out to the sides of the stereo image. Put another way, the Mid is whatever the left and right channels have in common, and the Side is the difference between the left and the right channels.

Subtle cuts and boosts to the Mid or Side on the master bus can go a long way towards taming or enhancing the stereo image.