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using the Apple USB audio interface driver
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using the Apple USB audio interface driver



I have a device that needs USB audio support in MacOS 9, for which I am
planning to write ASIO and USB audio drivers.  I am just double checking
to make sure I cannot use Apple's USB audio class driver with my ASIO
driver.

My undertanding is that if my device is a USB audio device it should
match with the Apple USB audio driver.  This driver then interfaces with
the Sound Manager, so in other words the API to access the USB audio
device then becomes the SOund Manager.  In addition, if my output device
is not a speaker, specifically as defined in the USB descriptors in the
output terminal type, then it is not claimed by the system as the default
output device.  This would allow me to open it and talk to it via an ASIO
driver.  The input also would be available.  Is this correct?

The device needs to be switched between 16 and 24 bit.  Can I use Sound
Manager calls to set the bit depth, and would these calls translate to
having the Apple USB audio interface driver select an alternate
interface?  In other words, alternate interfaces are used to change
between different sample rates and bit depths, so I don't know how I
could get Apple's audio class interface driver to select alternate
interface #2, for example.  If going through Sound Manager wouldn't work,
would writing my own Composite driver (using the Apple example code) and
then having it call USBExpertInstallInterfaceDriver with my desired
alternate interface descriptor be a way to have the Apple audio class
interface driver select an alternate interface?

I guess the other issue would be latency, as this would add another
buffer copy step to intput and output processing.  I'd have to think
about how much this would add...

- jarrell
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