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MS microphone technique question.

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Brian Reynolds
MS microphone technique question.
on Apr 18, 2011 at 11:21:00 am

I'm very aware how the MS stereo mic works where it consists of 2 mic elements, a fig 8 and a cardioid mic, and where L= M+(S+) and R= M+(S-).
With that in mind it has me thinking...

If you had a single point source pulse (lets call it a gunshot, hand clap, door slam or cymbal hit as we are recording in the real world)

If that shot occurred at 90Deg L, the output of the MS matrix would be mainly [fig8 (+) and small amount of mid mic (+)]

If that shot occurred at zero Deg which is straight in front, the output of the MS matrix would be mainly
[mid mic (+) and fig 8 (+/-) which would cancel out]

If that shot occurred at 90Deg R the output of the MS matrix would be mainly [fig8 (-) and small amount of mid mic (+)]

If that shot occurred at 45Deg L, the output of the MS matrix would be [fig8 (+) and equal of mid mic (+)]

If that shot occurred at 45Deg R, the output of the MS matrix would be [fig8 (-) and equal of mid mic (+)]

So with that in mind the shot at 45Deg R would in fact cancel out (in the R channel) as you are combining a (+) signal from the mid mic with a (-) signal from the fig 8 mic. [if combined in equal parts]

I know all the theory and claims of MS but these are based on mathematical equations but is it in fact different in the real life?


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Ty Ford
Re: MS microphone technique question.
on Apr 18, 2011 at 12:26:34 pm

Hello Brian,

It all makes sense the minute you leave the theoretical for the practical.

Regards,

Ty Ford

Want better production audio?: Ty Ford's Audio Bootcamp Field Guide





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Brian Reynolds
Re: MS microphone technique question.
on Apr 18, 2011 at 1:57:52 pm

Here is a diagram that might explain the situation.
The green line is where the maximum cancellation will occur because M+ and S- one with a positive amplitude and the other with a negative amplitude will cancel each other. (the cancelation will be a dip where the M+ & S- overlap rather than a fine line)


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Noah Kadner
Re: MS microphone technique question.
on Apr 18, 2011 at 11:47:29 pm

Not an engineer but wouldn't it make a lot more sense to point your microphone directly at the sound you want to record and handle panning in your post mix? Preserve the options and all that?

Noah

Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Panasonic GH2 and Canon 7D.


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Brian Reynolds
Re: MS microphone technique question.
on Apr 19, 2011 at 8:32:53 am

Noah, let me describe it this way... If you had a group of say 5 singers or musical instruments (it could be a full choir or orchestra) positioned around a MS stereo mic on a stand.

The person on the far left [singer 1] another singer along side [singer 2] then another [singer 3] which would be directly in front of the mic, then [singer 4] which will be further around and then finally [singer 5] will be on the far right of the microphone.

With the way the MS mic works is by using a matrix system to create a separate left and right signals, I have found that there is a null or reduction in sound level at 45 deg to the right, so [singer 4] would be down level in the recording.

This is caused by the sound from the [singer 4] point arriving at the 2 capsules in the mic, one of those capsules will give a + amplitude [mid mic] the other capsule signal is then inverted giving a - amplitude [side -], then when the + mid mic and - side mic are added in the matrix the level will be reduced. This how the null or level drops occurs with a MS mic setup.

I hope this explains it for you.


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Noah Kadner
Re: MS microphone technique question.
on Apr 19, 2011 at 3:13:03 pm

Way over my head- you should call up mr THX on that one...

Noah

Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Panasonic GH2 and Canon 7D.


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Marius Kunze
Re: MS microphone technique question.
on Apr 28, 2011 at 9:35:31 pm

Brian, I might be completely missing the point, but isn't there a -1 in the equation of the MS-Stereo-Matrix? That should be doing the trick even in theory.


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