[LAU] Latency and USB interfaces

[James Stone]

On Fri, Jan 10, 2014 at 7:48 AM, Clemens Ladisch <clemens at ladisch.de> wrote:
> Tim Goetze wrote:
>> [Clemens Ladisch]
>>> In most cases, the ALSA buffer/period parameters directly reflect
>>> hardware parameters, but in the case of protocols like USB where it is
>>> not possible to transfer data directly out of a ring buffer, there is an
>>> additional packet queue, which adds latency.  (The length of that queue
>>> is either constant or proportional to the period size, depending on the
>>> driver.)
>>
>> Thanks you Clemens for clearing that up.  How would one go about
>> determining the size of this queue between ALSA and USB?
>
> In the case of the current version of snd-usb-audio, the queue has the
> same length as the buffer, but never more than 18 ms.
>

Hi Clemens!

Is there anything that happened to snd-usb-audio (or the underlying
usb kernel code) between 3.0.36 and 3.6+ that might explain why it is
no longer possible to get clean audio with a frame/period size of less
than 128/2 using jack on the Scarlett 2i4?

James