[wdmaudiodev] Re: Audio over USB

  • From: BlazeAudio Developer <developer@xxxxxxxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Tue, 25 Feb 2003 17:40:37 -0800


I'm not sure if this is really related to the problem your are facing or
not,but, in general, if the data is to be streamed over an external bus, the
Stream class Minidriver model (or now the AVStream model) is more
appropriatethan using the port class miniport model.


At 08:58 PM 2/24/2003, Divya Vedagarbha wrote:

Hi All,

I have developed an audio minidriver based on the MSVAD framework to route 
audio data over a proprietary USB driver. It uses the port class driver 
interface. This USB driver transmits audio through the USB device to a 
remote wireless Headset (over Bluetooth). As per the USB driver 
requirements, it expects the audio to be pumped at 480bytes every 30ms. 
Audio driver exposes the audio capabilities as 16bit PCM with 8000 samples 
and as per the settings, audio driver is supposed to receive 160bytes every 
10ms from the audio subsystem. So, this ideally matches the USB 
requirements. However, I observed that the data flow is not smooth and 
there are breaks heard in the song heard on the headset. This shows that 
the rate requirements are not met. I also observed that the data received 
from the sub-system is not always 160. It varies between 32-128.

I tried an experiment where I transmitted an audio file directly over the 
USB driver satisfying the rate requirements. This works perfectly. The 
quality of audio is good. I am facing the quality problem only when the 
song is played over the virtual audio driver.

Could anyone suggest how to circumvent this problem?

Thanks &Regards


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