[wdmaudiodev] USBAudio sampling rate selection
- From: Robert Gruner <rgruner@xxxxxx>
- To: wdmaudiodev@xxxxxxxxxxxxx
- Date: Mon, 19 May 2003 14:13:59 +0200 (MEST)
Hi Everybody!
I've got a problem concerning the selection of a specific sampling rate on
an
USB-Audio-Class Device. I defined 2 discrete sampling rates in my Type I
Format
Descriptor which looks as follows:
Audio Streaming Format Type Descriptor:
bLength: 0x0E
bDescriptorType: 0x24
bDescriptorSubtype: 0x02
bFormatType: 0x01
bNrChannels: 0x02
bSubframeSize: 0x02
bBitResolution: 0x10
bSamFreqType: 0x02
tSamFreq[1]: 0x001F40 (8000 Hz)
tSamFreq[2]: 0x003E80 (16000 Hz)
Enumeration (Win98) is fine (except that CoolEdit Device Settings Dialog
shows 11 kHz
also supported (why?) but correctly refuses to record at this sample rate by
showing
MMSYSTEM008 Error).
Recording using the two supported sample rates works (with internally
generated signals
from the device).
But my Question is: How is the device told which sample rate to use? I have
to know,
because I need my ADCs to work with different master clock at different
sampling rates.
Studying the Audio Class Definition I supposed there should be an Endpoint
Request been
sent, which tells the sampling rate to use, but I do not receive such one.
So, is there a class specific request used for that purpose?
I could do the same thing by defining different alternate settings for each
sampling rate as
it has do be done with different bit resolutions but this does not seem to
be the easy way.
Thanks!
Bye, Robert.
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