ALSA resampling everything to 48kHz

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2605

Hello all,

I have a USB DAC that I just noticed is resampling everything I play to 48kHz. I'm guessing that ALSA is favouring dmix here, and that's what causing the problem. For instance, when playing a 24-bit/192kHz file with aplay, I see the following:

audiodef · Posted: Fri Feb 10, 2017 3:06 pm Post subject:

Yes, /etc/init.d/alsasound restart should work.

Hm, are you willing to experiment? I'm curious if resampling occurs if you use JACK and assign the output to a JACK-capable client.
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Wallsandfences · Guru Joined: 29 Mar 2010 Posts: 378

I'd try to explicitly route the aplay output to hw(0,0), this way, dmix is ruled out. Not at my box at the moment, man pages should guide you to the correct syntax.

Wallsandfences · Guru Joined: 29 Mar 2010 Posts: 378

you made me curious, man aplay shows there's a --disable-resampling switch, this should do.

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2605

I think that part of the problem here is that the device supports only S16_LE, S32_LE, and SPECIAL formats, but this particular file is S24_3LE:

swanson · Posted: Wed Feb 22, 2017 5:15 pm Post subject:

Documentation for ALSA can certainly be quite unclear but outputting directly to hw:2,0 should have bypassed dmix and allowed the application to choose the sample rate...unless it is maybe done as part of the format conversion from S24_3LE?!? Dmix only runs a single rate and format, usually 48000 and S16 for standard devices, but you can force the rate and format in dmix with something like the following (mine just sets the dmix rate to 44100);

NathanZachary · Moderator Joined: 30 Jan 2007 Posts: 2605

Thanks for posting your ALSA configuration. I figured out that, in Audacious, I can set it to hw output/32 (instead of float), and that fixes the problem. However, I obviously then lose any type of mixing (so I'm limited to one stream at a time). So, it's a toss-up on what's better. I personally could barely hear a difference (especially at the relatively low volume at which I typically listen), so I think that just leaving it with the default mixer might be the way to go for my needs.

Cheers,
Nathan Zachary
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Wallsandfences · Guru Joined: 29 Mar 2010 Posts: 378

Akkara · Posted: Thu Feb 23, 2017 10:15 am Post subject:

Does your USB card really go up that high? Most that I've seen cap out at 96K. EDIT: nevermind, just read your link, wow, it seems that one goes to 384K!

Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

That's a thing pulseaudio provides, though it's limited to only two sample rates set at startup (the default is CDDA+48kHz). I also note it doesn't seem to work with common programs and resamples in software anyway...

dimko · Apprentice Joined: 12 Feb 2006 Posts: 196

Alsa by default sets sample rate to 48K.

You need to modify .asoundrc

So those were bad news.

More bad news.

Firefox and Chrome dont like anything above 48K in sample rate and refuse to work.

There is nothing we can do about it, as Firefox officially dropped support for alsa and only support hated pulseaudio.

So only ugly workaround - to switch off browser if if you want to use above 48k sample rate.
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