[alsa-devel] Buffer size for ALSA USB PCM audio

[James Stone]

At 32 frames/period (reported round-trip latency 1.33ms), it starts up
but there are too many xruns for it to be usable.

James

On Thu, Aug 29, 2013 at 4:00 PM, Alan Stern <stern at rowland.harvard.edu> wrote:
> On Thu, 29 Aug 2013, James Stone wrote:
>
>> On Wed, Aug 28, 2013 at 7:46 PM, Alan Stern <stern at rowland.harvard.edu> wrote:
>> > On Wed, 28 Aug 2013, Clemens Ladisch wrote:
>> >
>> >> Sorry, what I said applies more to explicit sync endpoints.  When using
>> >> implicit sync, a playback URB is submitted for each completed capture
>> >> URB, with the number of samples per packet identical to the
>> >> corresponding capture packet, so the parameters must be identical.
>> >
>> > Got it.  Below is an updated patch.
>> >
>> > James, the problem you encountered was most likely a result of the
>> > faulty treatment of capture endpoints that Clemens pointed out.  It was
>> > quite obvious in the usbmon traces that the unpatched driver used 8
>> > packets per URB whereas the patched driver used 22.  This updated patch
>> > should fix that problem.
>> >
>>
>> Works fine. With this, it is possible to get clear playback at 64
>> frames/period too. With vanilla 3.10.9, there was some glitchy
>> distortion to the sound at that latency, so this seems to be an
>> improvement.
>
> That's good.  What happens if you push frames/period even lower?
>
> Daniel and Eldad, more testing of the most recent proposed patch would
> be welcome.
>
> Alan Stern
>