• Open Menu Close Menu
  • Apple
  • Shopping Bag
  • Apple
  • Mac
  • iPad
  • iPhone
  • Watch
  • TV
  • Music
  • Support
  • Search apple.com
  • Shopping Bag

Lists

Open Menu Close Menu
  • Terms and Conditions
  • Lists hosted on this site
  • Email the Postmaster
  • Tips for posting to public mailing lists
Re: CoreAudio and equalization
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: CoreAudio and equalization


  • Subject: Re: CoreAudio and equalization
  • From: Chris Rogers <email@hidden>
  • Date: Wed, 26 Jun 2002 17:07:38 -0700

To do equalization with FFTs is a little more complicated than that.
You need to do the processing on overlapping buffers in the same
way that a phase-vocoder does. Do a google search with keywords:

"overlap-add" "analysis" "resynthesis"

and you should find more info about this method. The basic idea
is that you not only have to window the signal, but you need to
move the window in increments smaller than the window/buffer size
(typically 1/4 or 1/8 the size). It requires a processing engine
somewhat more complicated than simply processing one buffer after
another....

The CCRMA web site has some info

Hope that helps,
Chris Rogers
Core Audio
Apple



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
_______________________________________________
coreaudio-api mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/coreaudio-api
Do not post admin requests to the list. They will be ignored.
_______________________________________________
coreaudio-api mailing list | email@hidden
Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/coreaudio-api
Do not post admin requests to the list. They will be ignored.

References: 
 >CoreAudio and equalization (From: john <email@hidden>)

  • Prev by Date: Re: CoreAudio and equalization
  • Next by Date: Re: CoreAudio and equalization
  • Previous by thread: CoreAudio and equalization
  • Next by thread: Re: CoreAudio and equalization
  • Index(es):
    • Date
    • Thread