[wdmaudiodev] USB Audio playback on Vista

  • From: Danijel Spasojevic <danijel.spasojevic@xxxxxxxxx>
  • To: wdmaudiodev@xxxxxxxxxxxxx
  • Date: Tue, 06 Jul 2010 11:19:07 +0200

Hi All,

We are trying to get some insight related to an issue regarding USB Audio Device playback.
We were performing a simple SNR measurement using a 0dB 1kHz sine wave as a reference (played back from Windows Media Player on a Windows Vista SP1 machine) and then stopping the playback or playing silence to take the SNR reading on an AP2722 system. We have noticed that Media Player or some audio subsystem on Vista actually doesn't stop the USB streaming after stop command and we see some dither in the digital audio data (this stops after 20sec or so and then zeros are streamed). In fact, playing silence in Media player (wav file with all zeroes for audio data) also results in dither (non zero samples).

Does anyone have any experience with this? Is there a way to disable the dither? Dither on silence is nothing else but noise and it costs
our SNR around 6dB. Is Audio Fidelity test in WLK affected by this? Is this the same in Windows 7?

Thanks in advance.

Best regards,
Danijel Spasojevic
Senior Application Engineer/UACB
Tel +381-(0)21-4801-185
Fax +381-(0)21-450-721

RT-RK Group
Fruskogorska 11
21000 Novi Sad
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