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CoreAudio and equalization
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CoreAudio and equalization


  • Subject: CoreAudio and equalization
  • From: john <email@hidden>
  • Date: Wed, 26 Jun 2002 23:44:10 +0000

Hello,

I'm not sure if this is appropriate for the typical type of question on this list, so forgive if it is not.

I'm trying to alter the audio data given in the recordIOProc in the frequency domain. The code does an FFT transform (using Don Cross's source), then uses this:

// in a loop the size of the buffer using i

z = realBuffer[i];
v = imagBuffer[i];

// calculate decAdjustment here

intensity = sqrt(z * z + v * v);
thetaValue = (z == 0.0) ? 0.0 : atan2(z, v);

intensity *= decAdjustment;
z = intensity * cos(thetaValue);
v = intensity * sin(thetaValue);

realBuffer[i] = z;
imagBuffer[i] = v;

Now doing this causes there to be static/fuzz in the audio. Looking around on the web I see that a windowing function may be needed to "smooth the edges" between alterations to the data in the frequency domain.

However, using the hamming window (or hanning or blackman) even without the EQ modifications causes the audio to sound weird!

Does anyone have any experience with this stuff that could help? Thanks!

-- John
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