Notes on Core Audio Implementation of PortAudio

by Phil Burk and Darren Gibbs

Document last updated October 18, 2002

WHAT WORKS

Output with very low latency, <10 msec.
Half duplex input or output.
Full duplex
The paFLoat32, paInt16, paInt8, paUInt8 sample formats.
Pa_GetCPULoad()
Pa_StreamTime()

KNOWN BUGS OR LIMITATIONS

The iMic supports multiple sample rates.
But there is a bug when changing sample rates:
   Run patest_record.c at rate A - it works.
   Then run patest_record.c at rate B - it FAIL!
   Then run patest_record.c again at rate B - it works!


DEVICE MAPPING

CoreAudio devices can support both input and output. But the sample 
rates supported may be different. So we have map one or two PortAudio 
device to each CoreAudio device depending on whether it supports 
input, output or both.

When we query devices, we first get a list of CoreAudio devices. Then 
we scan the list and add a PortAudio device for each CoreAudio device 
that supports input. Then we make a scan for output devices.