naturerecordists
[Top] [All Lists]

1. Re: M/S recording setup

Subject: 1. Re: M/S recording setup
From: "James Shatto" wwwshadow7
Date: Mon Aug 23, 2010 9:08 am ((PDT))
In my test I used sox to do ALL the generation and mixing.=A0 And audacity =
to do comparative analysis.

When mixing(RIGHT.wav) the common tone (3rd/C) between +M(MIDDLE.wav) and -=
S(SIDE_M.wav) cancelled out.=A0 Kind of expected, but really plays with the=
 gain levels of each channel.=A0 And the derived M/S (and -S) from the L/R =
matrixed file(STEREO.wav).

$ sox -t null /dev/null -s -2 -c 1 -r 48000 null.wav trim 00:00:00 00:00:30

Taking that null file and amplify in audacity (Effect -> Amplify), I get a =
new peak level near -40dB.=A0 (baseline)

Amplify of the Original +S (SIDE_P.wav) and Original -S (SIDE_M.wav), gave =
a new peak level near -34dB.=A0 Track -> Mix and Render && Effect -> Amplif=
y.



Amplify of the Orignal +M (MIDDLE.wav) and Derived -M (MIDDLE3.wav), gave a=
 new peak level near -24dB.=A0 Track -> Mix and Render && Effect -> Amplify=
.

Amplify of the derived +S (SIDE_P2.wav) and derived -S (SIDE_M2.wav), gave =
a new peak of 0dB.=A0 AKA audible results.=A0 Track -> Mix and Render && Ef=
fect -> Amplify.

Does it prove anything?=A0 Probably not as you're not likely to have much e=
xactly matching content between M and S in practical application.=A0 And it=
 could just be the quality of sox as an editor.=A0 Or audacity.=A0 Or the s=
ample rate / resolution.=A0 Or my math.=A0 And mixing was best guess since =
that plays with the gain.=A0 And that's probably not how one normally handl=
es M/S content.

But I would imagine that in any editor, if you were to mix M and S to L and=
 R, then save as.=A0 Then load the new file and derive M and S and derive -=
S, that S and -S wouldn't completely cancel each other out.=A0 Where in a p=
erfect world, they would.=A0 And is an indication that some degredation has=
 occurred.=A0 Perhaps not in the audible range since you have to amplify si=
gnificantly to notice.=A0 But enough in my test that the resulting +S and -=
S did have audible results.=A0 Perhaps not the typical editing path for M/S=
 either.=A0 And like I said probably doesn't prove much given the synthetic=
 / worst case scenario content.

It should be fairly simple to test with any M/S content.=A0 Does the invert=
ed derived M cancel out the original M?=A0 Exact match, no degradation woul=
d suggest that it does.=A0 But it appears that it doesn't.=A0 If you're eff=
ectively adding a noticeable dB of junk per edit(even if it's not audible),=
 enough to motivate someone to do the matrix in post and not in the field.=
=A0 But it depends on what one considers good enough.=A0 And results probab=
ly vary greatly between software packages.

- James


--- On Sun, 8/22/10, Rob Danielson <> wrote:

<Prev in Thread] Current Thread [Next in Thread>
Admin

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the naturerecordists mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU