Notes on Core Audio Implementation of PortAudio

by Phil Burk and Darren Gibbs

Document last updated March 20, 2002

WHAT WORKS

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

KNOWN BUGS OR LIMITATIONS

We do not yet support simultaneous input and output on different 
devices. Note that some CoreAudio devices like the Roland UH30 look 
like one device but are actually two different CoreAudio devices. The 
BuiltIn audio is typically one CoreAudio device.

Mono doesn't work.

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.