David,
The key to understanding the *theory* of mid-side encoding and
decoding lies in understanding how figure-8 microphones work, with the
front and back 180 degrees out of phase. Once you understanding what
happens when in-phase and out-of-phase signals are mixed, look at the
formulas, and it will make sense. It's actually much simpler (and
thus more ingenious) than it seems at first.
The stereo perspective given by an ideal mid-side pair is
theoretically equivalent to that given by a coincident XY pair of
ideal conventional directional microphones. But in mid-side you can
control the spread simply by varying the relative gain of the mid and
side mics before
decoding them -- and because decoding happens in postproduction, you
can decide the width *after* you make your recording. You can
do this with regular XY, too, actually, by mixing that into M-S and
then back to XY, and most DAW software can do this. So in *theory*, M-
S offers no advantage to the digital recordist that a coincident XY
pair of ideal cardioids could offer.
But, as either Yogi Berra or John Von Neumann said, in theory, theory
and practice are the same, but in practice, they're different. And
here, the difference is that the theory requires *ideal* microphones,
which don't actually exist. In particular, XY and MS are the same
only to the extent that the microphones have a flat response across
their entire polar pattern, which no real mics actually do. The MS
techique can have a practical advantage over XY because of the way the
capsules are arranged, with the center capsule facing straight ahead,
and two capsules (the front and back of the figure 8) facing to either
side. This means that sounds from the primary subject, presumably
straight ahead, are dead on axis for the main microphone, where it
delivers the best frequency response.
So that's M-S vs. XY. But you asked about SASS. SASS is a totally
different animal, because it's not coincident, but rather quasi-
binaural. Personally, I really like the image that a SASS rig gives,
especially in the field. (Where do you get a SASS head modified to
take good mics? I'd love to put my MKH-8020s inside mine, which just
has the stock electric PZM capsules).
In any case, because SASS is a barrier-based separated mic technique,
and not a coincident array like MS is, you'll likely find results from
the two to be quite different for many subjects. Again, I like SASS a
lot for outdoor recordings, and you should definitely try to compare
your M-S rig with your SASS rig under various controlled conditions to
get a feel for how each will perform. Personally, if I had a modified
SASS head that would work with good mics, I'd use it quite a bit.
-matt
On Aug 3, 2009, at 19:42, David Kuhn wrote:
> Hi Recordists, as I mentioned in my last post, I have recently
> undertaken to learn the mysterious ways of the mid-side stereo
> technique, having gotten together an MKH 30/40 set with Senn MZW 201
> blimp windscreen and home-made furry cover.
>
> As Bernie has put it, mid-side technique is not intuitive like other
> systems we use. There seems to be no substitute for field/studio
> experience in getting to know how to use it. At this stage I've used
> it enough to know THAT it works, but have little understanding of
> HOW or WHY it works. I have used my SASS (Walt-modified with MKH
> 20's) for three years now, so simple, what you monitor is what you
> get. In fact I spend a lot of time just listening though that
> system. Listening through the mid-side system is, for me, not so
> satisfying or spell-binding, at least with the SD 702 set to "Inputs
> 1,2 linked for MS".
>
> Faced with two imminent extended field trips, I need to progress to
> some level of knowing when mid-side would be best to use, relative
> to SASS. It may be that I just need field time with it, using both
> systems when time and gear allows, then sort it out in post,
> manipulating the MS and comparing with SASS results. If, however,
> any of you MS veterans have guidance, pointers, or even
> commiseration, that would be welcome.
>
> Aloha,
> David
>
> >>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> David Kuhn
> www.soundshawaiian.com
>
>
> 808 335 0398
> Cell 808 651 8247
> Mail to: PO Box 1018
> Waimea, Kaua'i HI 96796
> <<<<<<<<<<<<<<<<<<<<<<<<<<<<<
mab blogs at http://www.crypto.com/blog/
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