Fidelity problem on Windows 7 if sample rates do not match.

[sullivang]

If you would like to try to reproduce the problem, here is the procedure for Windows 7:

1. Close SoundCheck, if it is open

2. Control Panel | Sound | Playback, click on your audio device that you will use in SoundCheck, Properties | Advanced (this assumes Classic view in Control Panel)

3. Now select a format that uses a sample rate of 48kHz. (either 16-bit or 24-bit should be fine) Click OK.

4. Open SoundCheck

5. Configure it for 44.1kHz, 16-bit

6. Test Tones | Create Tone, configure for a sine wave, 80% amplitude, 100Hz, duration 20 seconds

7. Click Play Tone, and you will probably hear the artifact.

8. Repeat the test, but use a sample rate of 48kHz in SoundCheck. The artifact will have gone.

This is the procedure I can use on my internal Realtek HD audio interface. For my USB interface, which has it's own control panel, I have to set the sample rate in it's own control panel. (Windows only allows formats that use whatever sample rate that is configured in the USB device's vendor supplied control panel - not sure whether this is correct behaviour or not - it may well be a problem with the driver)

Greg.

[sullivang]

Exactly what I suspected, and feared.

It is you who is confused, but it's not your fault.

Please read this blog carefully, and get back to me. (you don't need to read all the stuff about bit depth - concentrate on the information about sample rates)

http://blog.szynalski.com/2009/11/17/an-audiophiles-look-at-the-audio-stack-in-windows-vista-and-7/

I don't think you have digested what I said over on MSDN yet, either.

Changing the sample rate in SoundCheck DOES NOT change the sample rate of the audio interface, on Windows 7 (and, it seems, Vista).

Thanks,
Greg.

[David (PassMark)]

I suspect you might be confused.
If you are just talking about the output of sound (from your PC to your speakers) then there is no sample rate on the audio interface.

As there is no sample rate there is no possibility of a mismatch on output.

You set the sample rate in SoundCheck, and this is what you get from the card.

However on INPUT to your sound card there IS a separate sample rate, which is used recording (e.g. from Line in, or a Microphone). This can be set separately from the output rate used in SoundCheck.

And I think it makes some sense that if you set the output at a high sample rate, but set the input at a different lower rate you'll get artefacts when you are doing the recording.

If the input sample rate is impacting on the output quality then I would have to think this is a software bug (e.g. in the device driver).

[sullivang]

On Windows 7, if I configure SoundCheck to use a sample rate of, say, 44.1kHz, but configure the audio interface to use 48kHz, and then play a test tone, I hear a ringing artifact. If the sample rates match, the sound is pure.
I am using a low frequency sine wave (circa 100Hz), because the ringing seems most noticable for low, pure tones.

As far as I can tell, back on Windows XP, Sound Check would AUTOMATICALLY change the sample rate of the hardware to match - that's how XP worked. (unless more than one application had the device open simultaneously).
So, customers who are unaware of this change in behaviour may not BOTHER to check that their audio interface is configured to match the rate they select in Sound Check, and it could cause erroneous results. I.e, they may assume that their audio interface will be set to match Sound Check automatically.

This issue seems to have a more serious impact, however, because I am finding that a lot of web content is not playing cleanly, if my audio interface is set to 48kHz. (which is actually the DEFAULT sample rate of my netbook's internal Realtek HD interface).

I have reported my findings to the Windows Pro Audio Developer's forum:
http://social.msdn.microsoft.com/Forums/en/windowspro-audiodevelopment/thread/725546ce-57bf-40d0-b7aa-47e51de9c3ae

Aside from the change in behaviour regarding the sample rate of the audio interface, there seems to be a problem regarding sample rate conversion on Windows 7, if the WaveOut API is used. As far as I can tell, sample rate conversion for WaveOut, on Windows XP, works fine. It's the combination of these two factors that results in the audible artifacts.

Greg.