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AUGraph Problem
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AUGraph Problem


  • Subject: AUGraph Problem
  • From: "Christopher O'Neill" <email@hidden>
  • Date: Sat, 12 Apr 2008 16:27:01 -0700

Hello all,

I am fairly new to CoreAudio, and am learning new tricks all the time. I wrote a program a few months ago using callbacks and AudioFileIDs which, in a nutshell, opened 4 different files, changed their pitches independently, mixed them together, and finally played them through the default audio source. Although this worked, it was a pain to write, since I had to mess with all of the raw bytes of audio data myself to add all of these effects.

Recently, a friend of mine told me I should look into the AUGraph API to simplify things. I am now rewriting my code to use this API, and although it is a TON cleaner than my original version, it seems to have one major problem. I have my graph set up as follows:

AUFilePlayer --> AUPitch --> |
AUFilePlayer --> AUPitch --> |
AUFilePlayer --> AUPitch --> | --> AUMixer --> AUOutput
AUFilePlayer --> AUPitch --> |

If there is only one AUFilePlayer and AUPitch node going into the mixer, everything works great. However, even if I just increase the number to 2 there is a lot of crackling and noise, to the point where the sound is almost inaudible. Also, if I remove the AUPitch nodes, it sound fine. I constructed the same setup in AULab, with 2-4 generators reading from files, each with an AUPitch effect, and all being mixed into one output, and it made the same noise. However, it also came up with a warning triangle telling me that "The audio engine has received an overload. Mute unneeded tracks and reduce the number of effects in the document to reduce CPU usage."

Am I trying to do too much? Is there something I can do to simplify my setup? I am pretty sure all of the nodes I have are necessary to get the desired result, and it doesn't seem like this is a very complicated graph, but maybe I am trying to do too much. My original code was able to manually work with 4 different files just fine, so it shouldn't be a processor limitation, but just in case it matters I am on a Macbook 13" with 2 GHz Intel Core Duo, 1.5GB RAM, about a year and a half old.

Does anyone have any suggestions as to how to fix this? Thank you in advance.

	-Chris
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