[wdmaudiodev] Re: sample rate control on Vista

  • From: "Jeff Pages" <jeff@xxxxxxxxxxxxxxxx>
  • To: <wdmaudiodev@xxxxxxxxxxxxx>
  • Date: Tue, 18 Jul 2006 09:52:52 +1000

Related to this, I was wondering if there's any way the driver can indicate its preferred default sampling rate and bit depth, or does Vista always set this to 44.1kHz 16-bit regardless of the capabilities of the hardware.

Jeff Pages
Innes Corporation Pty Ltd

----- Original Message ----- From: "Dugan Porter" <duganp@xxxxxxxxxxxxxxxxxxxxx>
To: <wdmaudiodev@xxxxxxxxxxxxx>
Sent: Tuesday, July 18, 2006 9:40 AM
Subject: [wdmaudiodev] Re: sample rate control on Vista



Hi Nikolay.  Here's a multi-part answer for you:

1. There is no programmatic way for an app to set the mmsys.cpl capture rate, because the Vista philosophy is that no audio app can make configuration changes that affect any other apps. The setting in mmsys.cpl is only meant to be changed by the user.

2. If an app uses the legacy APIs (waveIn and DirectSoundCapture) to capture audio at a rate other than mmsys.cpl's, the system will convert from the mmsys.cpl rate to the app's requested rate using a sample rate converter.

3. However, if an app uses the new WASAPI API in exclusive mode (by using the AUDCLNT_SHAREMODE_EXCLUSIVE flag), it can open the device in any format supported by the driver, and no SRC will be used. The downside is that no other app will be able capture audio.

4. If you need to use a legacy API, you can at least *discover* the system capture rate setting using the new Vista APIs, and then capture at that rate, to avoid the SRC; however this doesn't let you *control* the rate.

Hope that helps -
Dugan Porter - Game Audio Team - Microsoft
This posting is provided "as is" with no warranties, and confers no rights


-----Original Message-----
From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Nikolay V. Pyatkov
Sent: Sunday, July 16, 2006 3:22 PM
To: wdmaudiodev@xxxxxxxxxxxxx
Subject: [wdmaudiodev] sample rate control on Vista


Hi,

We have an input only WDM portcls audio driver on Vista 5456. The driver can
support 48,000 and 44,100 sample rate. The application needs to open this
driver at 48,000. Here is the code:


WAVEFORMATEX wf;
wf.wFormatTag = WAVE_FORMAT_PCM;
wf.nChannels =  2;
wf.nSamplesPerSec = 48000;
wf.nAvgBytesPerSec = 192000;
wf.nBlockAlign = nBlockAlign;
wf.wBitsPerSample = UCODEC_BIT_PER_SAMPLE_PCM;
wf.cbSize = 0;

mmResult = waveInOpen(
&m_hWaveIn,
nInputDeviceId,
&m_WaveFormat,
(DWORD_PTR)m_hWaveInEvent,
 0,
CALLBACK_EVENT);

mmResult is 0.

But the trace in the driver shows:

00000431 9.63108540 ValidatePcm :
00000432 9.63109016 ---- cbSize         = 22
00000433 9.63109398 ---- nChannels      = 2
00000434 9.63109875 ---- nSamplesPerSec = 44100
00000435 9.63110352 ---- wBitsPerSample = 16

The Vista audio subsystem took the parameters from "Audio
Devices->Recording->My Device->Properties->Options" .If I manually modify
value in the Options panel Vista will use the value to open my device.

I tried to check/uncheck "exclusive control" box. Does not help. How do I get
control over the bit rate back to the application?


Thanks,
Nikolay








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