Mid-Side manipulation of stereo signal...

Discussion in 'Mastering' started by brad, Apr 1, 2002.

  1. brad

    brad Guest

    1] In your mixer, pan the first piece (1&2) as a normal stereo track of music, hard left and right.
    2] Next, pan the second track (3&4) dead center for both channels. This will make the track mono.

    3] Now phase reverse both channels of 3&4.
    If you kept the tracks sample tight, when you play, you will only hear the stereo information - anything common to both channels (mono) will go away. If you bounce this resulting output to a stereo file, you have the side information isolated for further processing (we'll call this 5&6) . Now, if you mute 1&2 (leaving only 3&4 in mono and phase-reversed) you can bounce this resulting output for your mono information (we'll call this 7&8). If you line up the 5&6 and 7&8, they'll recombine, giving you your normal stereo output.
     
  2. Thanks Brad!
     
  3. Brad Blackwood eloquently explained:

    Brad, your explanation makes total sense, except, wouldn't you have to phase-reverse the bounced mono track (now 7&8) again (bringing it back in-phase) before adding it in?

    Also, do you need to reduce your levels before summing (panning) L and R? In Protools, I hit over 0dBFS on the Master fader (using an extracted song from a CD so each track by itself has peaks at 0dBFS).

    Does this depend on the pan behavior of the individual DAW or desk, and how do you determine what to do? I guess it isn't trivial whether the pan just sums or whether it also scales? Am I making this more complicated than it is?

    When you mix M and S back together, it makes sense they should be mixed back together at equal levels, right? So, if I need to reduce L and R by -6 dB before panning to M, I should also bring down the S tracks by 6dB, correct?

    Sorry for not being nearly as coherent in my questions as you were in your explanation. I am just trying to wrap my poor brain around the concept. :eek:

    Thanks!

    Michael Kiaer
    New York City
     
  4. Dave McNair

    Dave McNair Active Member

    Michael, I think you keep the mono tracks phase reversed, because you might want to eq or compress center information only and to do this corectly you need to effect the phase reversed mono so that it will sum properly with the side information.
     
  5. anonymous

    anonymous Guests

    Wow!

    Thanks!

    I completly did NOT understand, but it is written down and I can follow it!

    :)
     
  6. damster

    damster Member

    When bouncing 3&4 to become 7&8 , is 5&6 muted or are you combing 3&4+5&6 to get 7&8? :confused:
     
  7. brad

    brad Guest

    ...
     
  8. brad

    brad Guest

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  9. brad

    brad Guest

    ...
     
  10. Kev

    Kev Well-Known Member

    OK that's Middle and Side ... or Sum and Difference.

    But I have been trying to find a way of making Left - Centre - Right... easy you say. I don't think so.

    The centre is not mono. and if I could get centre I could get Left only and Right only. I have tried various I-r and r-l configs but I just cannot get centre only info.

    How did Dolby do it? Am I missing something simple here? I have been avoiding hooking up my old ProLogic decoder as it would be a cop-out.
    :confused:
     
  11. brad

    brad Guest

    ...
     
  12. Kev

    Kev Well-Known Member

    I think you are wrong but now have to set up a test mix to prove it???

    I'm sure a signal hard in one speaker doesn't appear in the centre channel. Also the left and right are independant signals so you could change the left right balance whereas the side of m/s doesn't allow for this. Am I making sense?
     
  13. Kev

    Kev Well-Known Member

    I'm still working on this??

    I had a few guys at work today scribbling on paper ... l-r ... r-l L-(l-r) no L-(r-l)
    no phase change the whole thing ?? Thats mono again!.. then we moved into a control room and tried?? Didn't get much work done for about an hour.

    Later in the after noon one guy .. not from the original group, collected a few of us together and said "I've got it"

    No he didn't have it! :D

    I'm not giving up .... now where did I put that ProLogic decoder?
     
  14. brad

    brad Guest

    ...Originally posted by Brad Blackwood:
     
  15. Kev

    Kev Well-Known Member

    We are still working on it.
    :D
    ... and I still can't find my old ProLogic decoder.
     
  16. Ronny Morris

    Ronny Morris Guest

     
  17. Kev

    Kev Well-Known Member

    I give up... :(

    stereo doesn't not give L-C-R no matter how many phase changes and l-r and r-l and take away the number you first thought of etc....

    I did find the ProLogic decoder and it does seem to do more than just Sum and Diff but I haven't worked out what they have done.

    However it is not as defined in the L-C-R as I had remembered.
    ;)
     
  18. brad

    brad Guest

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