[wdmaudiodev] Re: Why USB Audio Class

  • From: Tim Roberts <timr@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Fri, 15 Jan 2010 09:52:53 -0800

swarna jakka wrote:
> Is there any clarity or any further advantages compared to jack
> supported audio devices?

You're thinking about this in the wrong way.  The jack is completely
irrelevant.  The wires from the jack connect to some audio hardware in
the computer.  Often, that audio hardware is a PCI device or a
PCIExpress device, but it's entirely possible for the jack to be wired
to a USB audio device inside the box.

> USB supports more number of channels.

That is false.  I could easily design my computer to have 5-channel
audio input jacks, whether the audio hardware is PCI or USB.  In fact,
USB Audio Class is MORE limited than other audio device types, because
the bandwidth cannot exceed 1 MB/sec.  So, you cannot run a 192k
24-channel signal through USB Audio Class today.

Now, it's true that most commodity hardware only installs a stereo jack,
but that has nothing to do with the underlying technology.

> One more question i would like to ask, is there any comply test for
> USB audio Class device.

The USB Implementor's Forum has some compliance tests, and the DTM suite
has tests for Windows audio devices.

Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.


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