M/S (Mid-Side) mic technique and the black magic of mixing different phases in audio!

Special Interest Groups Recording Techniques
1

I just tried the Mid Side mic recording technique today for the first time and I’m in awe with the black magic f*ckery that results from mixing mono signals with different phases…

Step 1: set up the mics according to M/S technique (cardioid pointing at you, figure of 8 above, vertically aligned, rotated 90º).

Step 2: start recording and talk directly at it, then from the left, then from the right…

Step 3: Split stereo to mono, take the figure of 8 signal, duplicate, invert phase on the copy, pan one all the way to the left and the other all the way to the right

Step 4: mute the cardioid mic track and play only the other two… the voice seems to come always from the center… Stronger when speaking from either side, as expected in a figure of 8 at 90º, but it sounds like it’s always coming from the center…

Step 5: Unmute the cardioid track and play all 3 tracks together… voila! black magic happens and now you can hear the voice shifting from left to right…

For those of you that know this technique I’m sure you’re not excited about this, but to me it was a true WTF moment! And I’ve been using Audacity and recording stuff (sparsely) for many years…

I just want to experiment more with different/unusual mic setups now :grin:

PS: greetings to the “old gang” Steve, Koz, Bill and Peter, I hope you’re all still around and having fun with Audacity!

2

There’s a plug-in called “Channel Mixer” that provides a preset for M/S encoding / decoding. Click on the “Details” to display the plug-in’s documentation.

3

Sweet! I always enjoy your plugins Steve!

I didn’t seem to have that plugin pre-installed on my very outdate version of audacity (2.4.2) (I still haven’t updated Debian to Bookworm on this machine), but I just downloaded and enabled it and it works like a charm!

I used to use your other plugin to generate stereo from a mono track, but I’m now experimenting with 2 mics. M/S technique was the one that impressed me most so far!

4

The Channel Mixer plug-in has never been part of the Audacity bundle. It’s always been an optional plug-in. I was hoping to eventually convert it to C++ as a built-in effect (with L/R level meters for each channel), but there were always other priorities, and then Audacity was acquired by muse group.

5

Hi Bruno,

great to hear from you again

Peter.

6

That is a shame! They should put all your plugins in there!

I was a bit worried when I saw the news about Audacity being acquired by muse… but Debian is still packaging it, so I guess it remains free software!

7

Yes it remains open source.

The license has been bumped from “GPL v2+” to “GPL v3” (I believe that was mostly so that Audacity can use VST3)

8

there’s a free real-time Voxengo plugin for mid/side conversion …

I can testify it works in Audacity2&3 on Windows.

9

Thank you for the suggestion!

They don’t seem to provide a linux version of it, though to be honest I don’t really need real-time conversion… On linux it should be possible to do it without plugins though… just some some (software) rerouting with jack or perhaps with ardour.