Tag Archives: near field compensation

Optimised Stereo II – Near Field Compensation

How far away from you are your loudspeakers – are they within a couple of metres of where you’re sitting? If you’re in a home/project studio then I’m going to assume that they are. They might even be as close as a metre from your listening position!

So what? Why does it matter how close they are? Well, you’ve heard of the proximity effect when you record with a microphone, yes? It’s the bass boost that you get as you move nearer and nearer to the microphone. Well if you’re sitting nearby the your loudspeakers then this can happen as well. And it’s not just the bass boost because there’s an associated phase difference that goes with it. This can cause some issues with where we localise the sound at low frequencies.

It was suggested by Michael Gerzon in his 1992 “Metatheory of Auditory Localisation” that this should be corrected. He states

“It might be argued that the effect on localization at such low frequencies is “unimportant”, but we believe this not to be so insofar as the more things that are made correct the better.”

With that in mind, and in the spirit of experimentation, I’ve made a very simple VST plugin that does this. I haven’t had a chance to listen to it in a decent room (mine is currently untreated, but not for long) so I don’t know how well it works. It’s definitely a subtle effect in from my preliminary listens.

Basically it’s a case of taking your stereo signal right before the output, splitting it into Sum (L+R) and Difference (L-R) channels and high-pass filtering the difference channel. These are then recombined back into L and R before being output via your loudspeakers.

I don’t know if Gerzon was right but this sort of near field compensation (NFC) is very common with Ambisonics so I thought it’d be worth giving it a go for stereo. I’ll be very interested to hear what other people think: important or pointless?

I’ll try have the VST up tomorrow. I just need to write up some brief documentation for it this evening.