IMHO, 441 samples for your circular buffer size looks way too small. I
would pick a much larger value, if I were you. I would not be surprise if
a so small value could confuse CoreAudio. All the audio interfaces I have
show a Max IO Buffer Size greater than 4096. Usually, the IO Buffer size
is set to 512 frames (but to be able to provide that size, your circular
buffer must be at least twice as big).
Have you look at how your driver responds to:
kAudioDevicePropertyBufferFrameSize = 'fsiz',
kAudioDevicePropertyBufferFrameSizeRange = 'fsz#',
It does not harm latency to have a big circular buffer. CoreAudio always
tries to write the closest possible to the "Tape head". But if there is
more room on the tape, there is less risk for an overrun and CoreAudio
feels happier.
Fred
2014-10-29 16:14 GMT+01:00 hagen <[email protected]>:
> Hi all,
>
> I must admit I am pushing it, but (test-wise) I configure my CoreAudio
> server plugin with a 10ms circular buffer (i.e. 441 sample frames at
> 44.1kHz, following is all at 44.1kHz), accordingly the plugins answers
> kAudioDevicePropertyZeroTimeStampPeriod request with 441. No matter how the
> plugin answers the kAudioDevicePropertySafetyOffset request DoIOOperation
> (kAudioServerPlugInIOOperationWriteMix) is called with upto 441 sample
> frames and a sample time of upto 610+safety offset sample frames in the
> future.
>
> Why does CoreAudio think the plugin can receive 441 sample frames at once
> (when a non-zero kAudioDevicePropertySafetyOffset was provided?) and why
> does CoreAudio think the plugin can handle upto 610+safety offset+441
> sample frames in the future?
>
> CoreAudio (via HALLab Default device alert) seems to call DoIOOperation at
> least 150 sample frames in the future. Which is an inherent “safety offset”
> of 3.4ms.
>
> What would be the minimal and what the optimal buffer size in sample
> frames (or msec) the CoreAudio server plugin should provide? Does this
> scale well with high channel counts?
>
> Cheers and thanks,
> Hagen
>
>
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