| Additional M/S info
After reading this discussion I had some thoughts that might be useful. Maybe you guys already know this stuff, maybe not:
1) M= mid mic signal (mid mic can be cardiod, omni or figure 8) You can also think of this as the "Mono" component of signal that shows up in both the L and R decoded stereo channels.
2) S= side mic signal (side mic must be figure 8) This is the "Image" component that is added in-phase to the L channel and out-of-phase to the R channel (L= M+S , R= M-S). The amount of S signal added to L and R determines the stereo image width.
3) As you've noted, the decoding can happen in hardware or software. Software has the advantage that image width can be determined at mixdown. BUT if the original mic array placement was not good, you can't correct that. Hardware decoders have the advantage that you check out mic placement realtime. Then you can record decoded or undecoded, as you choose.
4) Hardware decoding via 3 channels on the mixer can yield less-than-wonderful sound because critical side channel signal usually goes thru an extra channel strip adding non-symmetrical noise/distortion and phase errors. It can sort of "mush out" the stereo goodness. That's why we put M/S decoders in our preamps that are minimal,passive and symmetrical.
5) When you get up close with an M/S mic array, and you get the main axis a little off center, you can get really unbalanced R and L. That's 'cause M and S can become almost equal. (Substitute S=M in the little formula in 2) and you can see why.)
Sorry to be so long-winded. Hope this is helpful in some way!
Tim
TRUE systems |