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audio levels drop when playing multiple mixer inputs
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audio levels drop when playing multiple mixer inputs

  • Subject: audio levels drop when playing multiple mixer inputs
  • From: Bob Sabiston <email@hidden>
  • Date: Mon, 06 Aug 2012 14:38:07 -0500
Hello,

  I was having a problem with this a few weeks ago, and I never got it resolved.   I am using audio units on the iPhone, a mixer and a remoteIO output unit.

I have several inputs on the mixer, and they are all the same type of thing, a callback which renders sound samples into a buffer.  I've noticed that if I play one input at a time, it plays at full volume.  However, if I have 3 or so at the same time, the volume drops a lot.  

I've tried setting the output volume at various levels, and that changes the overall sound volume, but it still does the same thing.  If multiple sounds overlap, the volume is cut way down from it's original level.

I've tried setting the volume on each mixer input using this:

   OSStatus result = AudioUnitSetParameter (
                                             mixerUnit,
                                             kMultiChannelMixerParam_Volume,
                                             kAudioUnitScope_Input,
                                             inputBus,
                                             newGain,
                                             0
                                             );
But this seems to have no effect.  If I follow up the 'SetParameter' call with a 'GetParameter' call, it shows the volume to be whatever I set it to.  But the sound is always the same.  Anyone know what I am doing wrong?  

Thanks 
Bob

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