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USB Class Driver
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USB Class Driver


  • Subject: USB Class Driver
  • From: Lubor Prikryl <email@hidden>
  • Date: Mon, 31 Jan 2005 08:59:14 +0100

Hi,

Thanks to kindness of Bill and Doug from CA team I had learned a few things about USB Class compliant driver (CCD). Maybe it will help the others who might be surprised by its behavior.
I have some more questions I wish to have answered.

Facts:

- USB devices with CCDriver appear as two independent audio devices (2 IDs)
- They publish a contiguous interval of sample rates (e.g. anything from 32000 to 48000 Hz or even from 5990 to 50100 Hz)
- They publish physical Format with sample rate equal to zero.

Questions:

- Is the uncertainty in SR a property of the driver or of the device? Of every device? I tested YAMAHA speakers and M-Audio FastTrack, both of them allow any frequency in certain range.
- How to install notifications across input and output? If I change SR for the input of FireWire device, I obtain a notification for output, that the device had switched the output SR to the same value as I had set for input. Because of asynchronous behavior I am waiting for the message to handle SR change in my app. With USB CCD, I have two devices so the notification goes to another device than I need.
USB CCD does not change SR for both devices simultaneously, so I have to change for two devices at once. But how to find the proper pair, e.g. if I have more than one device of the same type? It requires a different approach (even different from Audio MIDI Setup) to change settings for input and output device always simultaneously, i.e. twice.



Lubor Prikryl
DSound (CZ)
Audio Software Developer

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