[Alsa-user] alsa loopback in 384khz

[Olivier Schmitt]

Hello,

I juste whant to ask the community how can we use some alsa loopback in
384khz or 768khz sample rate.

Dont ask me why, the reply is that i am an radio ham and we use lot of
loopback for signal processing.

But for somme reason we need more than 192khz of sample rate.

Thanks in advance dear community members.

[Caleb Crome]

Post by Olivier Schmitt
Hello,
I juste whant to ask the community how can we use some alsa loopback in 384khz or 768khz sample rate.
Dont ask me why, the reply is that i am an radio ham and we use lot of loopback for signal processing.
But for somme reason we need more than 192khz of sample rate.
Thanks in advance dear community members.

Heh, sounds like fun. What hardware would you be using? I've often
thought of projects where I need higher sample rates (like doing bode
plots of power supply and opamp stability). It would be handy if
there were a simple way of getting to those rates directly as sound
samples so I could use the regular audio processing chain I'm familiar
with.

-Caleb

Post by Olivier Schmitt
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[Clemens Ladisch]

Post by Olivier Schmitt
how can we use some alsa loopback in 384khz or 768khz sample rate.

The upper limit of 192 kHz is hardcoded in the snd-aloop driver.
Changing it would require recompiling it. Are you able to do that?


Regards,
Clemens

[Clemens Ladisch]

wget ftp://ftp.alsa-project.org/pub/driver/alsa-driver-1.0.23.tar.bz2

Do not use that package; it is outdated. The ALSA drivers are part of
the kernel.

nano ./drivers/aloop-kernel.c

sound/drivers/aloop.c

=>
...
.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_768000,

This entry is wrong; replace it with

.rates = SNDRV_PCM_RATE_CONTINUOUS,

.rate_max = 768000,

Yes. You also need to change the number in loopback_rate_info().

Can I juste compiling the allop module or i must compilling and install all?

If you have the source and the exact configuration of your running
kernel, it would be possible to recompile only this driver. But if you
do not know what you're doing, compiling the entire kernel is safer.

https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel
https://wiki.ubuntu.com/KernelTeam/GitKernelBuild


Regards,
Clemens