Topic: Guidance on when to midside and when to XY?

[page]

I've been thinking about this for the last couple of days, and I've gone back and read some of DSatz's posts and other stuff (notably http://taperssection.com/index.php/topic,82960.0.html ), and I've run MS before with results that I think sound better than ass.

So I'm curious, what venue/acoustic/setup conditions might cause someone to run XY *over* a midside configuration? I personally seem to favor midside recording because of the flexibility in post, and on a lark I ran XY this past weekend and the results turned out pretty good, so I got to thinking about what factors would go into deciding when to run XY over MS.

[boojum]

It is my understanding that XY gives the best localization.  MS has the benefit of very good localization and you can fiddle with the mid-side amounts.  If I am not sure of a venue I like MS just because it allows me to tweak the sound in post.  XY what you get is pretty much what you get.

[DSatz]

Page, both X/Y and M/S are categories of stereo recording technique rather than being just one specific setup. They both allow a fairly wide range of choices as to specifics. For example X/Y can use cardioids, supercardioids, hypercardioids or figure-8 microphones of any type (ribbon, condenser, small, large, pink or purple) as long as both are the same type and are at the same point in space (in the horizontal axis, anyway); in addition to the many different kinds of directional microphones that can be used, the angle between their main axes is another variable that you can set to suit your taste.

M/S involves a sideways-facing figure-8 microphone and a forward-facing microphone of any type and pattern in a coincident pair--but as to the further specifics, you're entirely free to choose as you see fit.

So it's not as though these two techniques each had one definite type of sound character to offer. Being coincident techniques, they're not inherently as "spacious" sounding as spaced microphones can be--but then again that's true of them both, and isn't a basis for choosing between them.

--best regards

[illconditioned]

I haven't done a comparison, but I've run both under different conditions.

MS is nice because you can vary the width in post.

Aside from that, I would choose the confuration where the caps point most directly to the sound source(s), and so they have the least indirect sound, eg., reflected off walls at the sides of the venue.

So, if you're far away, use MS, everything hits the mid capsule mostly head on (and use a very narrow image).
If you're close, and there is a PA on both sides of the stage, use XY, with one mic pointing to each speaker.

Oh yeah, Always get closer!

  Richard

[page]

Thanks for the replies folks. +T

I can see the points about if your in a venue you don't know or stuff. I guess one of the things that stumps me is, if your going to run at the stage lip, would it be preferable one way or another? Stuff like that, what factors would play into the game-time decision to run one config over the other.

For example, tonight at TLG, I ran MS for both since I didn't know whether I'd get to change at setbreak and we were told to move our stands midway through, so fearing I'd be under or near a wall, I ran MS so I could bandaid problems later.

[DSatz]

Page, as you know there's a matrix involved with M/S recording (or playback, depending on how you prefer to work--I always record the M and S signals directly, and matrix only in playback).

With the very same matrix (hardware or software), you can derive a perfectly valid M/S recording from any X/Y recording. This follows from the basic algebra of the approach. In M/S, L = M + S and R = M - S; to carry out the reverse transform, solve the pair of equations for M and S, and you get M = L + R and S = L - R. And voilá--you can set the stereo image width and the reverberation ratio with an X/Y recording as freely as you can with M/S.

They are simply two different ways of making (or recording, or transmitting) the same recording. Do you know how FM stereo broadcasting works? The main carrier is modulated by the mono sum of the left and right channels, while a subcarrier is modulated by the difference between left and right. That's exactly the same as M/S, but the outputs of a stereo FM radio or tuner are of course dematrixed to left and right before they're presented to the world, and for mono you just ignore the subcarrier. For "variable blend" you regulate the amount of the difference signal you feed into the matrix; for "crossblend" (to reduce high frequency noise) you put a low-pass filter on the difference channel.

Similarly, stereo LPs are cut such that the horizontal modulation of the groove is determined by the mono sum of left and right, while the vertical modulation is the difference. So you could think of FM and vinyl both as basically using M/S as their storage/transmission medium. It's a technique with many, many applications.

In the end, which technique you choose might be a matter of convenience, or whether you have a particular setup that you like for use in the conditions of a given venue. There is no categorical difference at all in the sound that you get.

--best regards

[Will_S]

In the end, which technique you choose might be a matter of convenience, or whether you have a particular setup that you like for use in the conditions of a given venue. There is no categorical difference at all in the sound that you get.

And this is the key point here.  In the abstract, given an arbitrary selection of microphone types, you can achieve similar results with XY vs M/S.  For instance if you run the usual cardioid mid mic along with a figure 8 side mic, the result is much like running hypercardioids in an XY configuration.

But for the OP, running a BSCS-L microphone which is a single point stereo microphone with selectable patterns (http://www.busmanaudio.com/bscs_l.html), the choices are a bit more constrained.  Running XY hypercardioids is not an option.  Basically his choices are:

XY cardioids
XY Figure 8s (i.e., Blumlein if at 90°)
M/S using either a cardioid or omni mid.

My take on these options:
Blumlein is great if you can set up in a spot that has both the perfect ratio of direct to reflected sound AND is just the right distance from the source so that the angle over which you are getting stereo information is neither too big nor too small.  Basically you want the sources that will spread from speaker to speaker on playback to subtend an angle of 90° (maybe just a bit less for safety) in front of you.  When everything goes your way, it sounds great.  But in real life taping situations, you can pick up a lot of chatter from the rear-facing lobes, which are every bit as sensitive as the front.  Also, it can be a bit lacking in bass.

XY cardioids - very compressed image unless you are very close to the source (ie the source subtends a very wide angle in front of you).  You can improve this somewhat by having the microphone capsules pointed more widely apart, but with LD mics you don't want to run at a super wide angle or you run into ragged frequency response to sources straight ahead, and you get a lot of reverberent information which is not good if you are far away from the source.  As DSatz mentions, you can later play around with the width of this recording using an M/S matrix in post, but your starting point will be the equivalent of XY cards rather than XY hypercardioids - i.e. there is no way to matrix/dematrix a pair of cardioids to really match what you get from a card + figure 8.

M/S with a cardioid mid (never actually run an omni myself, though it might be worth trying way upclose) - usually the best real world compromise.  Mixes down to what is effectively XY hypercardiods, with the virtual hypercardiods getting a little fatter and angled closer together as you add more mid, and that get more figure 8 like and wider apart as you add more side.  This will IMO give you a better stereo image than XY cards most of the time.  At least on my LSD2 (a similar LD stereo mic) it tends to result in a more pleasing frequency response than XY cards as well.  YMMV.

But for the real world, with your mics, I'd recommend XY cards at 90° if you are onstage or stage lip, M/S if you are further back.  Blumlein if you can stick the mic in the perfect spot acoustically and imagewise, AND it will somehow be isolated from crowd chatter in that location.