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17th October 2009
#1

Calculate the phase cancellation of 2 signal

Dear All

I'm trying to calculate (and plot) the audio information that is lost with the combination of two signals, more specific two microphones on a snare drum. According to my limited knowledge I can calculate the difference of two summed channels as follows:

Signal A + Signal B = Signal C
Signal A (Reversed polarity) + Signal B = Signal D

Signal C (Reversed polarity) + Signal D = DIFFERENCE

Now I have the difference between two signals. I would like to calculate what exactly what one is losing in both instances (straight or inverted polarity summation of A + B), but can't figure it out. I suspect that an answer might be found by reintroducing the calculated difference to the original signals.

Any guidance would be greatly appreciated.

Regards,
Gerhard Roux
20th October 2009
#2
Lives for gear

Hmm...well, you have

C=A+B
D=B-A
C+D=A+B+B-A=2B
D-C=B-A-A-B= -2A

Of course two mics on a snare will have delay effects that result in complex comb filter response.

Not sure what you're getting at.
Is that what you wanted to know?
20th October 2009
#3

Thank you Les, I'm getting closer. I also suspect that the arc tangent of the ratio of amplitudes will give a vector that can be used. I'm going to visit my parents over the weekend and will ask my mother to solve my problem for me. (True).
20th October 2009
#4
Lives for gear

Verified Member
20th October 2009
#5

Thanks Dave! This helps a lot. This formula is a good starting point, I think it will be possible to replace the angular displacement of the sine wave with a more complex pattern. Wish I was smarter....

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