On 3/15/23 18:18, Fons Adriaensen wrote:
On Mon, Mar 13, 2023 at 10:20:01PM +0100, Giso Grimm wrote:I am not an expert on USB driver / kernel implementation, but measurements show that the timing of jack callbacks using USB sound cards is not regular. When calculating period time histograms I usually get two or three peaks, only on rare occasions (e.g., 1ms block sizes, but not with all sound cards) only a single peak. Often, none of the peaks is related to a 1 ms grid.Did some test here, results at <http://kokkinizita.linuxaudio.org/linuxaudio/timing/results.html>
Very nice plots. Well almost, even though it's in the description I'd expect axes to have labels :)
In case of P = 96, N = 3, do the 5 outliers cause x-runs, or is it really just a clock difference? Have you calculated the average clock speed for all settings? I'd be interested if in the case P=48 N=3 the babyface's clock is also a 50ppm slow.
The clustering around 1ms multiples reminded me about that old post: https://linuxmusicians.com/viewtopic.php?f=47&t=10707 (Frame & Period settings ideal for USB interface).
-- robin
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