Vincent Yu wrote:
> Will any sample rate conversions occur with this .asoundrc config?
>
> pcm_slave.force_24_bit_no_rate_convert {
> pcm "hw:0,0"
> format S24_3LE # Or other 24-bit format
> rate "unchanged" # Necessary?
> }
>
> pcm.my_new_default {
> type plug
> slave force_24_bit_no_rate_convert
> }
http://www.alsa-project.org/alsa-doc/alsa-lib/pcm_plugins.html#pcm_plugins_plug
This plugin will not do resampling.
> Specifically, does sample rate conversion still occur anywhere in the
> signal chain even though I provided the "unchanged" string for rate?
The hardware, another plugin layered on top of this, or some application
might still do resampling. :)
> I would like to create a configuration to force digital audio output
> from my PC (Arch Linux - ALSA only, no Pulseaudio) to remain at or be
> converted to 24-bit format without any sample rate conversion.
Then try the linear plugin, which changes only the sample format:
pcm.my_new_default {
type linear
slave {
pcm "hw:0,0"
format S24_3LE
}
}
(The "plug" plugin does nothing but dynamically inserting other plugins,
such as "linear"/"route"/"rate", when required.)
> I understand that the word, "lossless," in the title may be a bit of
> a misnomer, since quantization noise from quantization errors during
> bit depth conversion will raise the noise floor of the signal by
> a small (and probably inaudible) amount
Converting between integer sample formats does not change the bits; you
get quantization errors only with volume changes.
> looking at the code and trying to grep directory trees recursively for
> the string, "unchanged", to see if I can get any leads, I got lost in
> the behemoth of a code base
The "unchanged" string is parsed in pcm.c; in pcm_plug.c, search for
"== -2".
Regards,
Clemens
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