AFMG Network Forum

Langston Holland · Member

Hello:

Assume a situation where one unknowingly records an inverted IR due to a polarity reversal somewhere in the measurement chain. At a later date when the acoustic measurement is impossible to retake, how would one correct the inverted IR including all affects to phase?

I tried the simple approach of multiplying the inverted IR by -1 and this corrected the shape of the raw IR and moved the phase 180 degrees upward as well. What was NOT corrected was the overall shape of the phase curve. In one test where the noninverted measurement was made of a simple loopback, the phase curve had a gentle "frown" to it. The inverted measurement changed this to a mirror image "smile" which was not corrected by the multiplication process, although the center of the smile was moved from -180 degrees to 0 degrees as expected.

Any ideas on how to fully correct the phase curve in this situation?

Thanks so much again. :)

Bruce · Member

Langston,

You have used the correct procedure to account for a polarity reversal. The magnitude response of a polarity reversal always remains the same. The phase response is offset by 180degrees at each frequency which is what you would expect for a polarity reversal.

Your inverted measurement must not be identical to your inverted loopback measurement as the -1 multiplication of the IR should not turn a frown into a smile.

I have just made a 2 channel measurement of my EASERA Gateway. Channel 1 was non-inverted, and Channel 2 was inverted. The IRs are mirror images of each other, the magnitude response is exactly the same, and the phase response is exactly displaced by 180 degrees between the channels. If I multiply Channel 2 by -1 in the Time Domain, then all three displays are exactly the same.

Langston Holland · Member

Yes I see it now - sorry for the dumb question - I wish I could promise it to be the last. :) EASERA is amazing - I'm sold on it after one week with the demo. It's like Smaart without training wheels - a bit scary - but the things I can learn and do with this thing are exciting.