Mid-side decoding issue - Total silence from the two side tracks

  • Thread starter Thread starter quesne
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TalismanRich said:
That's the trick with M/S. The CAD is in figure 8 mode, and you copy the file to a second channel and invert it. Look at the picture of the Reaper setup I put above. You can see the two "side channel" tracks are inverted. Those are both the same file.

If you talk into the right side, the "left" side signal is effectively cancelled out by the inverted "left" side of the other track. The "right" side predominates. By itself, it sounds really hollow in the middle, though, so you had a cardioid mic to provide the center. You actually end up with a stereo image.
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Yeah I was being dumb - I forgot to duplicate the track and invert one side.
 
It's really more of an effect than it is true stereo.
 
The mid side mic technique, I mean.
 
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Not an effect, it's a technique, as valid as X/Y, AB, ORTF, Blumlein, Near Coincident, or DIN.
 
Absolutely NOT an effect. A stereo technique with precise spacial location that has absolute mono capability, but with the ability to vary the width afterwards. I use it for choirs and small ensembles in locations where you cannot get a space with speakers. So many times, before M/S I would discover back in the studio a 'hole' in the middle, or excessive separation that was really difficult to fix. M/S means you can simply adjust it to suit. Until about 15 years ago it was rare for me, but since then, I've used it more and more.
 
Looked at it with some proper tools and it is simply too much side and not enough mid, so small movements of the speaker have much bigger swings from centre. Reducing side and boosting mid seems to fix it. Maybe the close distance enhanced the left/right shifts. putting the two versions above each other and then putting a scope on both shows what is happening.
 
PorterhouseMusic said:
Stand corrected!:-)
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I think I get where you were coming from - You don't have discrete left and right channels,
but all of the same information is still there.
It's just stored differently, as sum and difference - I.E. information that's common to left and right on one track, and information that is not stored on another.

Not sure if people know this or not but you can take a regular stereo recording and process it in to sum+difference tracks.

Just import some stereo song, pan both channels (L+R) centre, bounce that to a mono Sum.wav
then, looking at the same tracks in your daw, flip polarity of one of them and bounce again to a mono Difference.wav

Sum.wav is equivalent to your cardioid centre mic and Difference.wav is equivalent to your figure 8.

If you now clear your session and process those two wavs like you would a M/S recording and bounce, you'll have your conventional stereo track back.



We've probably all got stereo width plugins which do this behind the scenes.
 
Steenamaroo said:
I think I get where you were coming from - You don't have discrete left and right channels,
but all of the same information is still there.
It's just stored differently, as sum and difference - I.E. information that's common to left and right on one track, and information that is not stored on another.
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I think my original comment was a result of reading somewhere that mid-side is not "true stereo" in the strictest sense.
 
Reluctant to wake Dave up but I think FM stereo is transmitted as mid/side.

It's such a great technique for a few reasons.
Of course it's very easy to adjust the perceived width but you don't have the concern of distances between microphones
or between each microphone and any given source,
so it collapses to mono perfectly and doesn't suffer from potential phase issues.

I'm pretty sure it's a lossless process.
If you were to do what I described with a traditional L+R wav, converting to M/S encoding, then back,
the result (polarity flipped) should null with the source.
 
The best way to describe m/s is a matrixed two channel source. Multiplex stereo is indeed the mono channel, with the second channel the left/right information on the subcarrier.
 
Hello All:

Wanted to give everyone a quick update: I finally have gotten this working with the Voxengo MSED plug-in in Reaper.

After all of the testing and troubleshooting (which I greatly appreciate
Thumbs Up smiley
), it seemed clear that the mono summing could be an issue in Reaper (config settings, routing matrix, channel sends, etc.) So I posted the question in the Cockos (Reaper) forums, and a few folks did help me get it working using the default track settings.

However.....when I tried to duplicate those "correct" parameters and behavior in a new project, I ended up with the same mono issue! So I turned first to the HOFA 4U Meter, Fader & MS-Pan plug-in, but....unfortunately I was not able to get it working. I then downloaded the Voxengo MSED plug-in, and a good Samaritan on the Cockos forum helped me work through it
Thumbs Up smiley


Anyway, I am hopeful this problem is in the past now. Thank you all sooooo very much for your help. It has been truly invaluable!
 
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Glad you found a workaround. Thanks for the update.
It's a shame you couldn't nail down the problem for closure - Seems pretty clear there's unwanted summing going on somewhere , as you say.

Ah well, at least you can get back to work. (y)
 
Yeah - that's too bad that you/we didn't get to a definitive understanding of what was causing that and how to solve it. It occurred to me to setup for mid-side and make a little clip using Reaper in order to try to help troubleshoot - but I'm right square in the middle of another project and super busy with work right now. I've never captured mid-side tracks with Reaper. Yet.
 
What might have been more useful would be to post the folder with the RPP and two audio files of a non working setup. That way we could maybe dissect the routing an look for an issue. We've already proven that the technique worked with the two files.
 
quesne said:
it seemed clear that the mono summing could be an issue in Reaper (config settings, routing matrix, channel sends, etc.) So I posted the question in the Cockos (Reaper) forums, and a few folks did help me get it working using the default track settings.
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It seems odd that the problem is within Reaper - maybe your settings are odd for some reason - maybe. you could post Screen Shots of the Reaper Settings.
 
I absolutely agree with you guys that it would be unfortunate not to get to the real bottom of this. The investigation thus far has been extremely educational for me :-)

Now that I have a plug-in “workaround” (aptly called by Steenamaroo), I am absolutely open to continuing the analysis of the cause of the separation issue. When I get home, I will find one of my non-working M-S projects (as per TalismanRich’s suggestion), zip it up, and post it here (y)

And I will also take some screenshots of the reaper track and routing settings, Papanate :-)
 
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