Re: kConverterPrimeMethod_None not working on Tiger
Re: kConverterPrimeMethod_None not working on Tiger
- Subject: Re: kConverterPrimeMethod_None not working on Tiger
- From: William Stewart <email@hidden>
- Date: Mon, 24 Mar 2008 12:56:05 -0700
On Mar 22, 2008, at 2:35 AM, Brian Willoughby wrote:
Hello,
I'm writing an AudioUnit which requires oversampling. I decided to
ditch the upsampling and downsampling code that I have in my arsenal
in exchange for the more flexible AudioConverter - especially after
seeing the quality comparisons. I obviously need to set
kAudioConverterPrimeMethod to kConverterPrimeMethod_None because an
AudioUnit cannot seek back in time, nor can it fetch future
samples. An AU must process the samples in the current buffer, and
none before or after (* see below). The documentation seems to
promise that AudioConverter will not ask me to pre-seek. However,
when I set up a stereo 4x oversampling conversion, with an AU buffer
of 512 frames, and I ask for 2048 output frames, my
AudioConverterComplexInputDataProc is given a request for 516
frames. In fact, it often is asked for 4 extra frames when testing
with auval. This would only make sense if I were using the Pre-seek
or Normal priming methods, but I am not.
No - its actually due to some rounding in the converter so that the
pull sizes are in 4 sample increments to facilitate better altivec/SSE
processing alignements.
You can use AUConverter directly to this work for you - just open the
AUConverter unit and then set the render quality and audio unit
property sample rate converter complexity property and you are good to
go
Bill
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