[Bug 14717] resampled sound is horrible

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=14717

--- Comment #84 from Alexander E. Patrakov <patrakov at gmail.com> 2010-12-27 12:17:20 CST ---
(In reply to comment #82)
> It doesn't look like there is any true default quality. You can set it to good
> or best or whatever but it all seem to depend on the soudcard drivers.
> I tried it with two different cards and the quality is different at the same
> windows setting.

After experimenting with sb16 and ac97 in kvm, I must conclude that their
Windows drivers use exactly the same resampler (I don't know if it is something
default or just a coincidence), and it is not a zero-order-hold.

Technique of the experiment:

1. Create a wav file with 44.1 kHz sampling rate, containing 15 or so seconds
of silence.

2. Create a wav file with 32 kHz sampling rate, containing several separated
pulses of a known amplitude. I did this with a python script.

3. Put the follofing in your .asoundrc (assuming that your card supports 44.1
kHz):

pcm.filetee {
        type file
    file "/tmp/out.wav"
    slave.pcm "hw:0"
    format "wav"
}

4. Start Windows XP in kvm as follows:

QEMU_AUDIO_DRV=alsa QEMU_ALSA_DAC_DEV=filetee QEMU_ALSA_ADC_DEV=hw:0
QEMU_AUDIO_DAC_FIXED_SETTINGS=0 QEMU_AUDIO_ADC_FIXED_SETTINGS=0
QEMU_AUDIO_DAC_TRY_POLL=0 QEMU_AUDIO_ADC_TRY_POLL=0 kvm -m 512 -soundhw ac97
-hda hda.dsk

(or with -soundhw sb16, but then you have to install the driver inside Windows
XP)

5. Transfer foobar2000 installer and test wav files into Windows XP.

6. Open the silent wav file in Windows Media Player and the crackling one in
foobar2000.

7. While the silent wav file is still playing, copy /tmp/out.wav somewhere
else.

8. Examine the resulting wav file with a hex editor.

9. Note a particular sequence of non-zero non-header bytes in sb16 wav file,
search for it in the ac97 wav file.

The worst quality setting has two or three output samples influenced by each
input sample, the medium quality has the response width of 29 samples, and the
best quality (default in the fresh XP install) has the response width of 79
output samples (1.8 ms). As I said, all of this is for the 32000 -> 44100 Hz
resampling.

Further experimentation with 8000 -> 48000 Hz resampling reveals that the worst
quality setting is in fact linear interpolation (so it is still better than the
current zero-order hold in wine).

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