Question

I’m setting up the following audio graph

File Player AU -> Varispeed -> Remote IO

When I run the graph I hear my audio mostly clearly but with a lot of static. However if I configure the graph as such:

File Player AU -> Remote IO (Removing the varispeed)

My audio comes through perfectly.

I realize this issue is solved by setting the stream format of one or many of these audio units. However, after reading number of document’s (including Apple’s) I’m completely lost as to where and how I need to set the stream format.

Do I need to explicitly set the AUCanonical format on the file player output?

Does the verispeed input need to be modified in someway?

Will the Remote IO unit automatically handle the verispeed’s output format?

Is there something I’m missing here?

Answer 1

I was able to solve my problem by getting the stream format from the output scope of the file player and assigning it to the output scope of the varispeed unit.

//Setup a container ASBD, and zero out it's defaults
AudioStreamBasicDescription asbd;
memset(&asbd, 0, sizeof(AudioStreamBasicDescription));

//Get the size of the ASBD for the get property function
UInt32 propSize = sizeof(asbd);

//Get the file player's output stream format.
AudioUnitGetProperty(mFilePlayer, 
                     kAudioUnitProperty_StreamFormat, 
                     kAudioUnitScope_Output, 
                     0,
                     &asbd, 
                     &propSize)

//Set the file player's ASBD on the output of the varispeed unit
AudioUnitSetProperty(mVarispeed, 
                    kAudioUnitProperty_StreamFormat, 
                    kAudioUnitScope_Output, 
                    0, 
                    &asbd, 
                    sizeof(asbd);

I think the makes sense based on Apples documentation… though I’m not sure why yet. I hope this helps some wayward core-audio adventurer…