We are talking about stereophonic recording techniques, correct?
Yes. Maybe someone else can explain this better than I can, for instance what DSatz says in the post I linked to:
The confusion, I think, is between two angles which have a cause-and-effect relationship, but aren't the same thing:
(a) the physical angle between the main axes of a pair of microphones, and
(b) the arc of sound from the original venue which they cover (specified as an angle).
The second of these is what Prof. Williams calls the "stereophonic recording angle," and in general, the wider you make (a), the narrower (b) will be and vice versa. That's the big paradox that I referred to earlier.
Most people assume that the wider they spread their microphones, the wider an arc they will cover. It's as obvious as the observation that the Sun revolves around the Earth ... and just as wrong. The arc that you cover with a stereo pair of microphones (coincident or closely spaced directional microphones, anyway) corresponds more or less to the area of overlap between their polar patterns. The wider you spread them apart, the smaller this area of overlap will be, and thus the narrower the angle of stereo coverage will be.
Whenever a direct sound source is picked up exclusively (or nearly so) by just one of the two microphones, it will appear to come from the location of the corresponding loudspeaker during playback. Usually you only want (at most) the very farthest extreme sound sources to be reproduced that way; often it's preferable for not even the most extreme left and right sound sources seem to come from the location of either loudspeaker. You don't want to "advertise" the loudspeaker's exact position, because stereo sound is an illusion and an auditory awareness of the loudspeaker position tends to spoil that illusion.
You want (this being an esthetic convention, i.e. something subjective that is nonetheless advisable because it's the generally accepted paradigm) the direct sound to be spread across "an appropriate amount" of the space between the loudspeakers, depending on how wide the original direct sound source was. A solo piccolo shouldn't fill the entire soundstage width, and actually neither should a solo piano, even if it's one of those huge, long Bösendorfer concert grands. Your choice of the microphone patterns and geometry (angle and distance between mikes, and distance from mikes to sound sources) determines the audibly "apparent" width (what the Germans call the "stereo basis width") that will be produced later over loudspeakers.
--best regards
But note that DSatz is talking about a pair of directional mics, whereas we are talking about omnis. But the basic point is the same--the stereo recording angle is not the same thing as the physical angle between the mics.
Imagine you are standing at the apex of an equilateral triangle with a guitar player at the corner of the triangle to your left and a banjo player to the right. From your position, they describe an angle of 60°. If you record them using a pair of cardioid mics, but place the mics facing directly ahead and directly on top of them, when you play back the recording both instruments will be equally loud in both speakers, with a mono recording the result.
Now say you keep the mics conincident but widen the physical angle between the mics to 90°. At this point, the guitar will be louder in the left mic, but still picked up quite a bit by the right mic. And when you play back this recording, it will image with the guitar to the left and the banjo to the right, but their images will not be spread all the way between the two speakers, instead the guitar will image a bit left of center and the banjo a bit right of center. This is because the stereo recording angle of cards XY 90° is 180° - sources need to be spread all the way over 180° as seen from the recording position to have their image spread all the way between the two speakers. As you increase the physical angle between the mics (say, to 135°) the stereo recording angle actually decreases - that is, sound sources don't need to be a full 180° apart to image hard left / hard right.
I believe the reference you sited is also referring to stereo recording angle in this sense. For ideal omnis, changing the angle between mics won't really affect loudness for sounds coming from the right vs. the left. All the stereo cues from omni recordings (without a baffle adding directionality, and aside from some directionality in high frequency content) come from timing differences due to the sound hitting one mic before the other. The further apart the mics are, the bigger the timing difference for the arrival of sounds coming from off axis. Thus, the farther apart the mics, the smaller angle (in reality) between sound sources needed to produce the same perceived angle between the sound sources on playback. Thus stereo recording angle decreases as the distance between mics increases.
Topic: Running Omnis??? (Read 14883 times)