Re: Stereo Processing

Subject: Re: Stereo Processing
From: William Stewart <email@hidden>
Date: Mon, 19 Mar 2007 15:47:47 -0700

Here's a modification of some code we use internally - the DSP decision can be done more optimally based on what your code ends up doing...

ComponentResult AUMatrixReverb::Render ( AudioUnitRenderActionFlags &ioActionFlags, const AudioTimeStamp & inTimeStamp, UInt32 framesToProcess) { AUOutputElement *theOutput = GetOutput(0); AUInputElement *theInput = GetInput(0); // get input source audio AudioUnitRenderActionFlags xflags = 0; ComponentResult result = PullInput(0, xflags, inTimeStamp, framesToProcess);

	if (result) return result;

/* this part uses an internal object to keep a track of any silent input, adjust for our decay/tail time and determine if it will actually produce data. If it doesn't then we just return a silent output buffer.

This is a nice optimisation, but can be bypassed initially

bool silence = xflags & kAudioUnitRenderAction_OutputIsSilence; mSilentTimeout.Process(framesToProcess, (SInt32)(GetTailTime() * GetSampleRate() ), silence );

	if(silence)
	{
		ioActionFlags |= kAudioUnitRenderAction_OutputIsSilence;

// clear out the destination buffer to match silent bit AUBufferList::ZeroBuffer(theOutput->GetBufferList()); return noErr; // silent output so tail should have died down by now; no need to process this time } else { // not silent output this time ioActionFlags &= ~kAudioUnitRenderAction_OutputIsSilence; } */

	int nOutChannels = theOutput->GetStreamFormat().mChannelsPerFrame;
	int nInChannels = theInput->GetStreamFormat().mChannelsPerFrame;

// call the DSP code - special case stereo->stereo if (nInChannels == 2 && nOutChannels == 2) { mDSP->Process( theInput->GetChannelData(0), theInput->GetChannelData(1), theOutput->GetChannelData(0), theOutput->GetChannelData(1), framesToProcess ); } else if (nInChannels != nOutChannels) { // if you want to do mono-stereo (or any N-M channel processing you need to take care of this result = unimperr; } else { // N-N channel processing for (unsigned int i = 0; i < nInChannels; ++i) { float* inputChannel = theInput->GetChannelData(i); float* outputChannel = theOutput->GetChannelData(i) mDSP->Process( inputChannel, outputChannel, framesToProcess ); }

	return result;
}

Bill

On 18/03/2007, at 6:39 PM, paul Fultz wrote:

ok thanks for the information, so if i overide AUBase
instead all I would need to do is overide Render() and
Reset(), right? and how would i go about coding the
Render() so that i can call Process()? i was working
on some of the code here i dont know if this is
correct, i kind of just compiled it together from
looking at other code:
ComponentResult		AUStereoBase::Render(
AudioUnitRenderActionFlags &	ioActionFlags,
											const AudioTimeStamp &			inTimeStamp,
											UInt32							inNumberFrames)
{
	bool ioSilence = IsInputSilent (ioActionFlags,
inFramesToProcess);
	ioActionFlags |=
kAudioUnitRenderAction_OutputIsSilence;
	AUInputElement *input = GetInput(0);
	AUOutputElement *output = GetOutput(0);

	AudioUnitRenderActionFlags xflags = 0;
	ComponentResult result = PullInput(0, xflags,
inTimeStamp, inFramesToProcess);
	if (result) return result;

	Float32 *sourceLeftP = input->GetChannelData(0);
	Float32 *sourceRightP = input->GetChannelData(1);
	Float32 *destLeftP = output->GetChannelData(0);
	Float32 *destRightP = output->GetChannelData(1);
	Process(sourceLeftP,
sourceRightP,destLeftP,destRightP,
inNumberFrames,ioSilence);
	return noErr;
}
also Process() is a virtual funcion in the class
AUStereroBase, which i will overide in my AU class.
also how can read number of channels in? i want do
something different if the input is mono, like call
Process() in this way:
Process(sourceLeftP, sourceLeftP,destLeftP,destRightP,
inNumberFrames,ioSilence);
thanks,
Paul
--- William Stewart <email@hidden> wrote:
We generally overide AUBase and just implement the
Render method -
then instead of working around all this stuff, you
just implement
what you need. I think its clearer and easier (but
many have ignored
me in the past!)
Bill
On 16/03/2007, at 6:47 AM, Christian Luther wrote:
Hi Paul!
Unfortunately there is more work to do. You also
have to modify the
function that creates the kernels
(MaintainKernels()) so that you
have your stereo kernel set up correctly (it
usually creates one
kernel per I/O which is not what you want). If you
want to support
stereo processing only you can just create one
instance of your
Stereokernel. If you want to support both mono and
stereo
processing you will have to do some more work
there.
Then, you have to modify ProcessBufferLists()
which is the function
that finally calls the Process() functions of the
kernels.
I can't really remember the details, but just look
around the
methods I named and try to understand what they
do. Then it
shouldn't be a problem to modify everything
accordingly. Hey, even
I got it to work! ;)
Greets,
Christian
Am 16.03.2007 um 00:01 schrieb paul Fultz:
ok thanks, well couldnt i create two classes like
myAUEffectBase
and myAUKernelBase, and have them inherit
AUEffectBase and
AUKernalBase respectively and just overide
ProcessBufferList() to
use myAUKernelBase, which will have an additional
function called
ProcessStereo() or would i need to overide other
functions as
well? also, where do i set the audio unit to only
recieve mono or
stereo, and set the output to only stereo?
thanks,
paul
William Stewart <email@hidden> wrote:
essentially yes (that's a
short version - there is a long version but it
would require
refactoring much of the code of AUEffectBase and
its kernel
objects that is probably too lengthy to go into
here I think).ï¿½
Bill
On 12/03/2007, at 1:52 PM, paul Fultz wrote:
I would like to set up my audio unit to process
stereo, is there
someway i can set it up so that it will call a
funtion like this
in my class to do the processing:
void ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
Process(ï¿½ï¿½ï¿½
const Float32 * ï¿½ï¿½ï¿½ inSourceLeft, // left
input
ï¿½ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½
ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½
ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ ï¿½ï¿½ const Float32 *
ï¿½ï¿½ï¿½
inSourceRight, //right input
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ Float32 *
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ inDestLeft, //left
output
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ Float32 *
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ inDestRight,
//right output
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ UInt32
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
inFramesToProcess,
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ bool &ï¿½ï¿½ï¿½
ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ï¿½ï¿½ï¿½ ioSilence)
i am inherenting AUKernelBase, and
AUEffectsBase, can i just
override ProcessBufferList() in my class? and if
so how would i
write the code to call this function that is
located in my kernel
(e.g. class myAudioUnitKernel : public
AUKernelBase)?
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From: paul Fultz <email@hidden>


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