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. > And is it correct to assume that in a best-case scenario where the > sample clock is synchronised to the USB clock Pro devices typically don't do this. > and the period size coincides with the interval at which USB frames > are signalled, This does not happen with Jack, where period sizes typically are a power of two. > the additional latency will be one period? These two conditions have nothing to do with the queue length; they ensure that USB interrupts happen exactly at period boundaries, i.e., that there is no jitter in the reported period interrupts. Regards, Clemens _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
