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Re: mid-side confusion

Subject: Re: mid-side confusion
From: "Borja Marcos" borjamar
Date: Thu Oct 4, 2018 9:57 am ((PDT))
> On 4 Oct 2018, at 16:10, Duncan Whitley  [naturer=
ecordists] <> wrote:
>
> Hi all
>
> Wondering if anyone with mid-side knowledge can help me out on this one. =
I made some recordings last night and in the dark mistakenly plugged the S =
into the left-channel of my recorder, and the M into the right. Usually thi=
s wouldn=92t be problem for me to rectify as I tend to record in MS on disc=
rete mono channels and decode later - however, on this occasion I decoded t=
o XY stereo inside the matrix box of the mic.
>

Fortunately MS encoding/decoding is a linear, reversible operation.

L =3D (M + S)  / 2

R =3D (M - S) / 2

If you have exchanged M and S you have two options.

1) Reverse the phase of the R you decoded from the exchanged ; and S

2) You can undo the process by getting the resultant XY decoding back to MS=
.. After doing that, exchange M and S and decode again

Something like:

M=97-\.                       /=97=97-\
        Convert to XY             =97-- Convert to XY again
S =97-/.                        \=97=97/


>
> Is it possible to recover the original M and S channels from the XY stere=
o decoded recordings? My intuition says =93no=94, but wondered if anyone ha=
d any knowledge on this.
>
> It=92s easy enough to derive the M and S from the XY stereo when the chan=
nels have been decoded to stereo correctly in the 1st place, but I=92m not =
sure in this case if it still works.
>
> Thoughts?
>
> Duncan
>
>





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