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Issues with M/S recording - 90 degrees off axis positioned in center Condenser Microphones
Old 31st December 2010
  #31
Hi Mike

I am not flaming you here, but do want to set the record straight.

Here is the text of the original Patent as it was reprinted in Streicher/Everest (my bold):

Quote:

(53) (1) Two velocity microphones are placed one with its axis of maximum response directly facing in the direction of the centre of the scene, and the other with its axis at right angles to that direction. Both moving strips are in line, and arranged so that this line is vertical, whereas the sound source moves in a horizontal plane. A performer speaking from the middle of the scene will affect only the face-on microphone, but if he moves to one side both microphones will provide outputs, while if he moves the other way similar outputs are provided but the phase of the edge-on microphone is reversed. Since the microphones are close together no phase differences are experienced between them and if their outputs are summed and differenced after a suitable amount of relative amplification the two final channels differ in magnitude in the correct manner for operating the loudspeakers to give the desired directional effect.

He does mention Omni's (referring to them as "pressure microphones") in other contexts within the patent, but not in the description of the Mid-Side microphone technique.

It's all semantics anyway, but Blumlein's original intent seems to have been to use only figure-8's (I don't think the cardioid existed yet in 1931).

But this paragraph also validates your point that there needs to be overlap between the mid and side pickups, else there is no imaging.
Old 2nd January 2011
  #32
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Sigma's Avatar
Quote:
Originally Posted by RobAnderson View Post
Hi Mike

I am not flaming you here, but do want to set the record straight.

Here is the text of the original Patent as it was reprinted in Streicher/Everest (my bold):

He does mention Omni's (referring to them as "pressure microphones") in other contexts within the patent, but not in the description of the Mid-Side microphone technique.

It's all semantics anyway, but Blumlein's original intent seems to have been to use only figure-8's (I don't think the cardioid existed yet in 1931).

But this paragraph also validates your point that there needs to be overlap between the mid and side pickups, else there is no imaging.
This coincident technique employs a bidirectional microphone facing sideways and a cardioid (generally a variety of cardioid, although Alan Blumlein described the usage of an omnidirectional transducer in his original patent) at an angle of 90° facing the sound source. One mic is physically inverted over the other, so they share the same distance. The left and right channels are produced through a simple matrix: Left = Mid + Side, Right = Mid − Side (the polarity-reversed side-signal). This configuration produces a completely mono-compatible signal and, if the Mid and Side signals are recorded (rather than the matrixed Left and Right), the stereo width can be manipulated after the recording has taken place. This makes it especially useful for film-based projects.

Blumlein Pair..is 2 fig 8's
Old 2nd January 2011
  #33
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doug hazelrigg's Avatar
Quote:
Originally Posted by DaanHendriks View Post
I have done tests using my Rode NT1a and NT2a, with the NT2a set to figure of eight and used as the side mic. This configuration behaves pretty much normally. The wider I set the MS width, the more pronounced the 90 degrees sound is placed at either hard L or R.
I think this provides the clue. When using a cardioid and a figure 8, they way a proper normal M-S is done, you find it works. But when you replace the mid mic with a shotgun, it doesn't. Although this baffles me somewhat, a shotgun mic isn't really intended for this use. What's wrong with using the two Rodes, if it works correctly?

I do M-S all the time, but I don't use decoders, I just set up a matrix correctly in my DAW, no need to decode. I assume this is what you meant by manual decoding.
Old 2nd January 2011
  #34
@ Sigma

Perhaps you missed my last 2 posts which quote the original patent filed by Blumlein in 1931?

Just in case, here again is Blumlein's definition of the pickup pattern of a velocity microphone:
Quote:
"Velocity or moving conductor microphones (e.g. moving strip)...These microphones give a response varying as the cosine of the angle of incidence..."
For the mathematically challenged: "the cosine of the angle of incidence" describes a figure of eight pattern.

Here again is the paragraph describing the Mid-Side technique:

Quote:
(53) (1) Two velocity microphones are placed one with its axis of maximum response directly facing in the direction of the centre of the scene, and the other with its axis at right angles to that direction. Both moving strips are in line, and arranged so that this line is vertical, whereas the sound source moves in a horizontal plane. A performer speaking from the middle of the scene will affect only the face-on microphone, but if he moves to one side both microphones will provide outputs, while if he moves the other way similar outputs are provided but the phase of the edge-on microphone is reversed. Since the microphones are close together no phase differences are experienced between them and if their outputs are summed and differenced after a suitable amount of relative amplification the two final channels differ in magnitude in the correct manner for operating the loudspeakers to give the desired directional effect.
Seems pretty clear to me that with the statement:

Quote:
Two velocity microphones
Blumlein is describing two microphones each having

Quote:
a response varying as the cosine of the angle of incidence...
meaning two figure-of-eight microphones.

When referring to omnidirectional microphones in the patent, he refers to them as pressure microphones, which are distinct from velocity microphones - a term which is used to describe ribbon microphones which are not omnidirectional in nature. There is no place in the patent that I have found where he ever describes using a pressure microphone in the manner described above.

Dead horse beaten I think...

quotes are from Streicher, Ron & Everest, F. Alton. The New Stereo Soundbook. Audio Engineering Assoc. 1998. p. A12
Old 5th January 2011
  #35
Here for the gear
 

Hello all,

I just wanted to confirm that after having done more tests, including the same test with the same microphone types (NTG3+MKH30) but different mics (a friend of mine owns them both as well), my basic conclusion is:

This combination is not ideal for MS if you want to capture a very wide stereo spread.

Other people have pointed it out already, but yes, I'm convinced of that now also. It will work fine for not-so-wide (i.e. within 45 degrees pickup angle) source, so for spot fx work it's good. But obviously, this is not the setup to use for any sort of ambience recordings.

I had read several times before that a shotgun is not ideal for MS, but now I see how it manifests itself, so it has been quite revealing. Interestingly, my friend did the same test with a MKH60/MKH30 setup, and even though that also revealed pretty much the same issue, it did sound a bit smoother. The jump from 90 degrees to 45 degrees wasn't as pronounced, so to speak. I presume it may have to do with the MKH60/30 combination being better matched in terms of frequency response curve.

What surprises me is that I got similar results with a Neumann 191 as with the NTG3/MKH30. You'd expect the 191 having better matched capsules (frequency wise) and therefore have more of a smoothness to it in the stereo pickup angle, as with the MKH60/30 combination, but in the tests I did at least this was not the case.

Thanks for your help, everybody.
Old 30th June 2012
  #36
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matucha's Avatar
History repeats itself . I've tried mkh60/30 and found out panning is "realistic" in narrow window of about 45 degrees and then it warps around and goes backward. Like if you used some kind of curved acoustic space (similar to curved mirror). I can see use in some focused fx recordings where there isn't a lot of ambience or noise around as the off-axis extremes would invade the center. Also some atmosphere recording use is possible if you don't mind the image warping, in some cases you don't really care about where in the image things happen or if it is confused sounding, because all you need is the noise .

MKH60 can sound tunell-like on ambiences like rain etc. It gets masked surprisingly well by the S channel.

To me 60/30 (or any shotgun/fig8) is a special case, no to be recommended as versatile MS solution. How is it with hypercardiods, is there some image warping too? Now I have to try my old MKH405 as the center...
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