Audacity Forum

Posted: **Sun Jan 22, 2012 10:43 pm**

Thanks for the M/S recording snippets sciurius.
I've added 4 new presets to the Channel Mixer plug-in:

M/S Decode Wide
M/S Decode Normal
M/S Decode Narrow
M/S Encode

The first three will decode M/S stereo recordings, assuming that the Mid channel is the upper (left) channel of the stereo pair.
The fourth preset will encode a normal stereo recording into M/S stereo with the Mid channel at the top.

That brings the number of presets up to 18 (plus the custom option) which is probably about the most that we would want. As different operating systems handle long menus differently, please can you check that the full list of presets is accessible on your machine. The first in the list is "Use Custom" and the final one in the list is "M/S Encode".

With M/S decoding it is not possible to know in advance what the exact peak level of the decoded audio will be until it has been decoded. In an extreme case a 0 dB side mix could produce an output with peaks up to 6 dB higher than either of the M/S channels, though that would be highly unusual. I've adjusted the presets so that hopefully the peak output level will usually be about the same as the peak level of the original audio, though depending on the phase differences between the channels it could actually be a bit higher or lower.

Please could you check on as wide a range of M/S recordings as possible that the output levels are reasonable and not excessively high or low. I can tweak the presets if necessary.

Do you think that the "Wide / Normal / Narrow" presets cover useful ranges? (not too limited and not too extreme?)

If you want "mono" then there is already a preset higher up the list "Both Left" which will do that.

channel-mixer.ny: (2.88 KiB) Downloaded 167 times

Posted: **Mon Jan 23, 2012 8:38 am**

steve wrote:As different operating systems handle long menus differently, please can you check that the full list of presets is accessible on your machine.

No problems here (Fedora Linux).

Please could you check on as wide a range of M/S recordings as possible that the output levels are reasonable and not excessively high or low.

No problems so far.

However, I was wondering whether it is possible to calculate the exact mix factors. For example, if the MID channel has a max level of 0.7 and the SIDE channel has a max of 0.6, the resulting channels would be limited to 0.7 (the max of both maxes) and the mix factors adjusted accordingly.

Do you think that the "Wide / Normal / Narrow" presets cover useful ranges?

This will require some more experimenting...

In earlier experiments with the channel mixer, I got satisfactory results with:

Code: Select all

	  (1 (list 100 0 100   0)) ; Mono
	  (2 (list 85 10  85 -10)) ; Extra Narrow
	  (3 (list 75 40  75 -40)) ; Narrow Stereo
	  (4 (list 60 60  60 -60)) ; Normal Stereo
	  (5 (list 40 75  40 -75)) ; Wide Stereo
	  (6 (list 10 85  10 -85)) ; Extra Wide

If you want "mono" then there is already a preset higher up the list "Both Left" which will do that.

Yes, although for the sake of completeness I'd suggest adding it to the presets nevertheless (but I can see why you want to keep the number of presets down...).

Thanks a lot!

Posted: **Mon Jan 23, 2012 5:54 pm**

sciurius wrote:However, I was wondering whether it is possible to calculate the exact mix factors

The peak value of the output for a given M/S file cannot be calculated without first applying the decoder and then measuring the output, but the problem with that approach is that, for Nyquist plug-ins, the measuring can only be done in RAM, so for long recordings the memory usage could be greater than the amount of physical RAM available in the computer, which would then cause Audacity to freeze or crash.

sciurius wrote:for the sake of completeness I'd suggest adding it to the presets nevertheless

I think that in most cases where a mono track was wanted, it would be better to simply split the M/S track (click on the track name then select "Split to Mono") and then delete the "Side" track (click on the [X] in the top left corner of the track).

I've been thinking that it may be better to have a separate Mid-Side decoder plug-in rather than just tagging it onto the Channel Mixer.
Which do you prefer for decoding M/S, the channel mixer or this one? (below)

Do you think that it needs the option for selecting whether the Middle channel is the "left" or "right" track channel? I've not seen a lot of M/S encoded files, but those I have seen have either been as two single channel files, or as a single channel Middle and a 2 channel Side file, or as a 2 channel file with Mid in the first (left) channel (like your files). I don't recall ever seeing a M/S 2 channel file with Mid in the second ("right") channel.

Posted: **Mon Jan 23, 2012 10:29 pm**

steve wrote:I've been thinking that it may be better to have a separate Mid-Side decoder plug-in rather than just tagging it onto the Channel Mixer.
Which do you prefer for decoding M/S, the channel mixer or this one? (below)

Asking trivial questions?

This mixer is very nice!

Do you think that it needs the option for selecting whether the Middle channel is the "left" or "right" track channel? I've not seen a lot of M/S encoded files, but those I have seen have either been as two single channel files, or as a single channel Middle and a 2 channel Side file, or as a 2 channel file with Mid in the first (left) channel (like your files). I don't recall ever seeing a M/S 2 channel file with Mid in the second ("right") channel.

I haven't seen am M/S with mid right (S/M ?) either so as far as I'm concerned this option can be removed. OTOH, it doesn't really get in the way of anything.

Thanks a lot!

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