On Sun, 12 Mar 2023, David W. Jones wrote:
On March 12, 2023 1:17:25 PM HST, Fons Adriaensen <fons@xxxxxxxxxxxxxx> wrote:
P N delay (ms)
------------------
256 2 11.369
192 2 8.702
128 2 6.035
96 3 6.702
48 3 3.702
P < 128 required 3 periods buffering.
P < 48 was unstable.
Ciao,
My limited experience with USB audio is that it required 3 periods.
At lower latencies that would be true, as listed above. Note that it is
stated periods less than 128 require 3 periods. This is because USB audio
does not send periods over it's wire but rather 1ms chunks that have to be
assembled into period sized buffers inside the computer. Those 1ms chunks
are not synced to the media clock but arbitrary size and timing. By the
time the period size reaches 128, there are enough 1ms cycles involved
that two period buffers work fine because they are an artificial construct
anyway. I am sure I have glossed over many details ... Basically, USB was
not designed with audio in mind. Also bear in mind that those who design
most consumer audio, consider 30ms or less as "low latency". I think even
8 or 16 foot pipes sound much faster than that.
Len
--
Len Ovens
www.ovenwerks.net
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