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Re: X-Y -> M-S & Perfect Reversals

Subject: Re: X-Y -> M-S & Perfect Reversals
From: "Lou Judson" inaudio
Date: Tue Mar 13, 2007 9:33 am ((PDT))
On Mar 13, 2007, at 9:02 AM, Walter Knapp wrote:

> You should be adjusting the gain on your recorder to optimum for each
> channel when you record, which would adjust for the extra output of the
> MKH80. Don't gang the gain of the two channels in M/S. Set each
> independently and correct according to your headroom preferences. This
> will give the optimum recordings to work with.
>
> Note that this usually results in a side that if mixed without gain
> adjust is too strong and tries to push the stereo wider than it wants
> to
> go. So, during decode you also adjust gain separately.

This is debatable. Until I got the SD 744 I always set the two channels
for natural sound in L/R, with the side set maybe 6dB down. Then it
approximates the final sound I wanted, with the sides remaining
adjustable on post or playback. I did my first (concert, not nature) MS
recording recently with the gains set equal (ganged), and it is
unlistenable without adjusting the gains on playback. But the sources
are well recorded... with 24 bit recording there is no need to boost
the side on the recording, there is plenty of both headroom and SNR or
bit use.

Caveat is that I do a lot more music recording than nature, but still
my approach works for both.

On another hand, adjusting the levels for appropriate soundstage width,
then reversing it to MS, will result in a corrected level that can be
played back in MS with decoding without the need to adjust the side
levels!

Side note - the SD recorders do not allow the ajustment of the relative
levels in the headphone matrix, so the only monitoring you can do is
the mic recording levels. In the future I wll lower the side mic by 6dB
for a natural monitoring sound. On the SD 7xx series, you can adjust
the relative level and still gang (link) the two channels, a big plus!

I don't think there is a hard rule on this, YMMV as you wish it to. LR
will reverse to perfect MS in any case, it just won't match the raw
tracks.

One more thing missing so far in this discussion - when working in the
computer with MS decoding, to keep perfect phase relationships between
the two channels, I find it neccessary to put the exact same plugs on
both channels, even of one is set to bypass, so any latency does not
throw the perspective off. I learned this from experience (as well as
theory) when taking live recordings done in LR or XY and splitting them
into MS so I can manipulate the center separately from the stereo image
(for example, if a music recording has the centered vocal too loud and
I want to tone it down or compress it without changing the stereo
field, I have to put the same compressor and/or EQ on both tracks even
if the side one is bypassed. Without the same latency on both, the
stereo perspective changed unpleasantly!). If your chosen software
automatically compensates for latency, then this may not be necessary.

<L>

Lou Judson =95 Intuitive Audio
415-883-2689





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