> Date: Fri, 20 Sep 2013 09:19:48 +0200
> From: Clemens Ladisch <cladisch@xxxxxxxxxxxxxx>
> To: "Robert M. Riches Jr." <rm.riches@xxxxxxxxxxxxxx>,
> alsa-user@xxxxxxxxxxxxxxxxxxxxx
>
> Robert M. Riches Jr. wrote:
> > I'm seeking suggestions for a low latency usb (or PCIE) sound
> > interface (or card). Or, maybe some good news that USB sound
> > devices are generally reasonably low in latency.
>
> All USB sound devices use the same driver and have almost the
> same latency.
Ahhh, thank you for that info. I think I figured out two ways to
measure the latency of a round trip through two devices and
associated software:
Manual observation:
1) Attach two USB sound adapters.
2) Attach microphone to card A's input.
3) Using 'unbuffer', run arecord on card A directed to aplay
on card B.
4) Attach headphones to card B.
5) Listen for gross latency.
More precise measurements:
1) Attach two USB sound adapters.
2) Connect source of analog sound to card A's L input.
3) Connect card B's L output to card A's R input.
4) Using 'unbuffer', run arecord on card A, tee to a file,
into aplay to card B.
5) View the saved samples in an oscilloscope program.
Now to find a device at a decent price that has stereo line input
rather than just mono microphone input...
> > The above setup initially used Mageia 1 on the main machine, and
> > life was good. Sound was essentially perfect. However, when I
> > switched the main machine to Mageia 2, kernel
> > 3.4.52-server-1.mga2, sound became hideously chopped. Somewhere
> > around 25% or more of the sound samples are being lost due to
> > xruns. Research into the problem showed snd_aloop was _NOT_
> > keeping time but would accept samples as rapidly as the playback
> > client would send them.
>
> This sounds like a bug in snd-aloop. Please try updating to
> a modern kernel.
That would be the ideal. I'd love to have the free time it would
require to compile the latest kernel and then test it to make
sure the distribution's userspace doesn't depend on something
unique to their older patched kernel.
Thanks again.
--
Robert Riches
spamtrap42@xxxxxxxxxxxxxx
(Yes, that is one of my email addresses.)
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