Re: Limitations on DefaultOutput unit format converter?
Re: Limitations on DefaultOutput unit format converter?
- Subject: Re: Limitations on DefaultOutput unit format converter?
- From: William Stewart <email@hidden>
- Date: Fri, 16 Oct 2009 15:10:56 -0700
I'd actually round up (probably to a multiple of 16), so in simple
terms:
maxFrames += 16;
maxFrames &= 0xFFFFFFF0;
I'd go up here as sometimes the rate conversions are at odd rates and
so the pull sizes from pull to pull are slightly different. an even
multiple of 16 samples should be more than enough padding to deal with
this.
Bill
On Oct 16, 2009, at 2:19 PM, Christopher Liscio wrote:
Bill, Doug,
It appears this problem was also occurring in my other code that
discovered this issue swapping out the GenericOutput unit.
So what I've done is the following, in both cases: (apologies if the
code doesn't come across)
UInt32 maxFrames;
UInt32 mfSize = sizeof(maxFrames);
NSXThrowError( AudioUnitGetProperty( outputUnit,
kAudioUnitProperty_MaximumFramesPerSlice, kAudioUnitScope_Global, 0,
&maxFrames, &mfSize ) );
Float64 israte, osrate;
UInt32 srSize = sizeof(israte);
NSXThrowError( AudioUnitGetProperty( outputUnit,
kAudioUnitProperty_SampleRate, kAudioUnitScope_Input, 0, &israte,
&srSize ) );
srSize = sizeof(osrate);
NSXThrowError( AudioUnitGetProperty( outputUnit,
kAudioUnitProperty_SampleRate, kAudioUnitScope_Output, 0, &osrate,
&srSize ) );
DEBUG( @"israte %f, osrate %f", israte, osrate );
maxFrames = maxFrames * MAX( 1.0, ceil( israte / osrate ) );
DEBUG( @"Adjusting maxFrames to %d", maxFrames );
// Set the maximum frames on the other audio units to jive with the
output unit's conversion rate
If you guys see any trouble in my logic above, please let me know.
Thanks for the great help, as usual!
Chris Liscio
http://supermegaultragroovy.com
Learn _your_ music with Capo: http://capoapp.com
On Oct 16, 2009, at 4:18 PM, Christopher Liscio wrote:
Bill,
On Oct 16, 2009, at 3:56 PM, William Stewart wrote:
I think what you are seeing is a max frames error.
...
Awesome. You are correct. However, ...
to fix this on the varispeed AU, you should set MaxFramesPerSlice
to be big enough to handle the IO request the output unit will
make on it (in the case above, I would set this to 2280)
...how would I programmatically determine what the proper value is
here?
I was under the assumption that I queried the output device for its
MaxFramesPerSlice and it'd give me a value that'd make sense given
the sample rate multiplier. I was using this Q&A article as my
basis:
http://developer.apple.com/mac/library/qa/qa2007/qa1533.html
...that, combined with the fact that the DefaultOutputUnit
basically wraps an AUConverter (among other things).
Do I instead want to query the input/output rates, and use their
difference as a multiplier to choose the value?
(Can you tell I hate magic numbers?)
I don't know why the 176.4kHz case is failing though, but if you
fix the above, I suspect that will work as well.
Your suspicion is correct. It fixed the problem here as well.
Thanks,
Chris Liscio
http://supermegaultragroovy.com
Learn _your_ music with Capo: http://capoapp.com
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