Mid - Side - Two or Three distinct channels?

[BouncyJones]

Hi,
I did a recording today where we had three inputs mix down to two within Cubase. Thus, we have

Left channel = mic on guitar (hard left) and vocal mic (down the middle)
Right channel = direct input guitar (hard right) and same vocal mic (down the middle)

I have great difficulty visualising this, but my common sense would tell that I could regenerate the three distinct channels. ie

Left Side = mic on guitar
Right side = direct input guitar
Mono = Vocal mic

I've tried following the advice of Katz and others within this forum on mid-side mastering but I have not been able to get the separate left and right sides. Is this even possible? I would really appreciate any one who takes the time to share their expertise,

Jon

[Cellotron]

Important to realize that the "Mid" channel is the mono sum of the L & R channels - and that the "Side" channel is the mono difference of the L & R channels - i.e. the 2 channels summed but with one of the channels phase inverted.

So - in this case if you encode to M/S you'll primarily get just the vocal (if it was indeed kept up in the center - as long as none of it leaked into the guitar mic!) in the Mid channel, and primarily both guitar tracks (panned hard left and hard right) in the Side channel.

Best regards,
Steve Berson

[minister]

M/S is derived from a 2-channel mix or a matrixed recording, front (mid) cardioid, sides figure of 8.

what you have there is a three track mix. different beast.

you can achieve sum and difference processing fairly easily on a console or in any DAW without any plugs except for the those of the polarity switching kind.

[BouncyJones]

Thanks for the responses,
Let me see if I can explain my confusion better.
I set up linked channels of L and R and then L and R reversed pan and polarity. When I have these all at the same level you can hear only the side. What I find confusing though was that I thought I would hear the R side on the R channel, and the L side on the L channel. Instead, it sounds like I'm just hearing the same through both. This is weird. ie, there was some vocal bleed on the mic channel of the guitar, so I thought that I could take the R side, which was the direct guitar input, and make that guitar more dominant. But it's not to be found! In other words, can I remove the Vocal from the Right channel so that the Direct Input Guitar is on its own?

Let me write this another way. Let's say my L channel is GV (guitar and vocal) and my R channel is DV (direct and vocal) then
GV - DV = GD (guitar and direct OR side)
GV + DV = V (mono OR mid)
DV - V = D
Is there no way just to get the D on its own?

Thanks for your patience,
Jon (I find this very difficult on my brain!!)

[minister]

ok...my brain hurts too, but i think i see what you did.

3 sources into two channels, so now you have a 2 channel mix.

here is a poor man's DAW Sum&Difference setup :

split L & R (which you already did). set the outputs to nowheresville.

Send L&R (equally) to mono Bus 1
additionally:
Send L to mono Bus 3
Send R to mono Bus 4

set up a mono aux channel and call it M (at least that is how i like to think of it...Mid.). set it's input to Bus 1 and it output to Bus 9-10 (stereo). you can put your eq, comp's and other processing here for the center.

set up two more mono aux channels, call them S 1 & S2 (sides). one with the input of Bus 3 the other with the input of Bus 4. set the outputs to mono Bus 5. on S2 (input Bus 4), pull up a plug-in that does nothing more than allow you to swap the polarity (in PT the Trim plug is good for this). swap the polarity.

setup another mono Aux, called S SUM and set the input to Bus 5 and the out put to Bus 7-8. you can put your Eq, comps and other processing for the side, here.

set up 2 more mono auxes, call them Side_L and Side_R and set L's input to 7 and the R input to 8 and the outputs of both to bus 9-10. Pan L fully left and R fully Right. on the R, pull up another polarity swapper. swap the polarity.

set up a stereo bus, call it 'Main Bus' it input to 9-10 and it output to you main monitor output. you can do more processing here.

hope that helps.

[Timecode]

Hi Jon, if you want a quick and easy way to go mid/side, Voxengo make a free plugin called the MSED that will do it for you.

My main question is why are you trying to do this in the mastering, when you have the individual channels in the mix anyway? If you want to put up the direct guitar just open up the session and put it up. As far as I can work out the only way to extract the direct guitar from the exported mix would be to sum the right channel with the phase inverted vocal track, which basically means you are adding the vocal and then taking it away again to give you the direct guitar on it's own.

As far as I can work out there isn't a way of extracting only the right or left 'side' information when working in MS - remember in an MS recording setup the side channel comes from one mic (the figure 8). If anyone has a technique I'd be interested to know it, but I have a suspicion it's impossible.

Cheers
Matthew

[Timecode]

Jon, just noticed your algebra is a bit off as well (mixing is adding, not multiplying). This may be one cause for the confusion.

GV - DV = GD (guitar and direct OR side)
Should be (G + V) - (D + V) = G - D (side channel)

GV + DV = V (mono OR mid)
Should be (G+V) + (D+V) = 2V + G + D (mid channel)

DV - V = D (what I said in the above post)

Cool, hope that helps, cheers
Matthew