REW 5.40 beta 135 / ASIO401 2.0: Sample rate mismatch (48/96/192 kHz)

[stef1777]

Hello,

I am experiencing a reproducible sample rate mismatch with REW 5.40 beta 135, ASIO401 2.0 and a QuantAsylum QA403 under Windows 11.

Configuration:

- ASIO buffer: 32768 samples
- Input: +18 dBV; output: +8 dBV
- FFT: 256k, Hann, 32 averages
- Test: Q17 Mini amplifier, approximately 1 W into 8 ohms

Observed behavior:

A mains-related spectral peak shifts depending on the sample rate selected in REW:

- 48 kHz selected: peak at 50 Hz
- 96 kHz selected: peak at 100 Hz
- 192 kHz selected: peak at 200 Hz

The 1 kHz test signal remains displayed at approximately 1 kHz. The behavior persists after restarting REW and reconnecting the QA403.

ASIO401 diagnostic log:

WARNING: ASIO host application never enquired about sample rate, and therefore cannot know we are running at 48000 Hz!

The inspected log shows a 32768-sample buffer interval of approximately 682.676 ms, consistent with 48 kHz rather than 192 kHz. No getSampleRate() or setSampleRate() calls were observed in that session. This strongly suggests a mismatch between REW's selected sample rate and the ASIO stream. The hardware sample rate has not been independently verified.

A very similar REW/FlexASIO issue was reported in 2018 and corrected in REW 5.20 beta 2:

FlexASIO doesn't honor the sample rate set in REW · Issue #31 · dechamps/FlexASIO

I've noticed something very strange while experimenting with REW 5.19 and FlexASIO 1.0: when the sample rate is changed in REW, it seems like it has no effect in FlexASIO, meaning that FlexASIO kee...

github.com

Could this be a regression in REW's ASIO sample rate initialization? Does REW reapply the selected sample rate after loading or resetting ASIO401?

Attachments:

- REW screenshots at 48, 96 and 192 kHz
- Anonymized ASIO401 diagnostic log
- Anonymized REW diagnostic archive

I have also reported this issue on the ASIO401 GitHub repository.

Thank you for your help.

 

[John Mulcahy]

REW expects the ASIO driver to honour the sample rate it requests, it calls setSampleRate for the rate it is running at and whenever the rate changes. On startup it queries the device for the rates that are supported (those are the canSampleRate entries in the 401 log) and makes those available in the sample rate selector.

 

[John Mulcahy]

To add to this, after REW sets the rate it reloads the driver and checks the rate it is running at, if the driver reports a different rate REW shows an Error message that the driver rate doesn't match the rate that was requested.

 

[stef1777]

Thank you, John, for the clarification.

I understand that REW calls "setSampleRate()" at startup and whenever the selected sample rate changes.

However, the ASIO401 diagnostic log reports:

<span>WARNING: ASIO host application never enquired about sample rate, and therefore cannot know we are running at 48000 Hz!</span>

The buffer timing (32768 samples every approximately 682.676 ms) also corresponds to 48 kHz, even though REW is configured for 192 kHz.

The spectral measurements are consistent with this: the same mains-related peak appears at 50 Hz, 100 Hz and 200 Hz when selecting 48, 96 and 192 kHz respectively.

I understand that the absence of <span>setSampleRate()</span> in the ASIO401 log does not necessarily mean REW never called it.

Would it be possible to check whether ASIO401 acknowledges REW's sample rate request, and whether REW verifies the actual rate reported by the driver afterward?

Is there any additional REW-side logging or diagnostic test we could perform to identify where the mismatch occurs?