At 8:48 PM +0000 3/12/07, John Lundsten wrote:
>JL- I recon (not 100% sure) if you set the decode with the same gain on
>both M&S, unity say. Then boosted / attenuated as needed the L&R output
>channels by the inverse of the amount used on the En-Code, you may (poss)
>get back where you started.
That's what I tried on test #4. Test #3 also without the +6dB gain.
http://www.uwm.edu/~type/audio-reports/M-SDecodeAccuracyTest/+matrix_2ndPlu=
gSettingsUndoFirstNoGain/
>
>BTW your original file is odd in that there is more S than M, IE unless yo=
u
>reduced the amount of S in the de-code your LR stereo will contain quite
>some amount of out of phase info - but that's odd
Its not unusual or detrimental; the mkh80 side mic has more output.
>It's not clear to me why you chose to use 6dB of gain ** on the decode mix
>bus?
Thats right, because Max suggested it.
>It's just possible there could be some rounding or other mathematical
>errors [stuff like plugin being 24bit & I assume Logic uses 32float
>internally]
Maybe,.. but the files cancel out perfectly on the same platform at
the unity positions.
>
>Rob, you could you try the following
>Take 2 mono files of, I suggest, Noise (any colour) & sine tone
>Use these as your MS inputs & encode to MS (sum & difference) note setting
>of non unity gain gain controls
>Decode - you need to be able to listen to just the L or the right output
>Whilst listenining to one speaker (as it were) adjust level of either chan
>till you get just noise or tone. Note gain setting & tell us.
Splitting the LR back into MS discretely is doable as best as I can
determine, its restoring the levels when side/mid gain adjustments
are used. I ran some reference tones and found that +3 dB mid boost
on the first plug is approximately corrected by a setting of -2.87
setting of mid gain on the 2nd plug and a -3dB side setting on the
side gain of the first plug is approximately corrected by +2.87
setting on the side gain of the 2nd plug. May not require the 6dB
boost. I suspect no setting will "nail" a perfect reversal if the LR
file is the product of mid and/or side gain adjustments.
Summary from my viewpoint: If I couldn't locate the M-S originals and
could only locate the LR output, I'd kick-up the file to 24 bits if
it was 16 bits and use the +matrix plug to get an M-S virtual state
if I needed to process it further like equalize. Its not as easy as
loading up the original MS->LR mix for me, personally, but its a
workable option. Rob D.
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