[PD] amplitude overload

Frank Barknecht fbar at footils.org
Tue Mar 16 19:19:04 CET 2004

Josh Steiner hat gesagt: // Josh Steiner wrote:

> weird... why?

Because USB audio is delivered in frames of which there are 1000
frames per second.  Running at 44.1 kHz means, that you have to pack
44.1 samples into one such frame. But there is no fractional sample so
you pack 44 samples for 9 frames, then 45 sample for one frame, repeat
ad infinitum.

This is not really compliant with how ALSA and Jack access the
hardware, which is with a constant period size that, per requirement
of Jack, also needs to be a power of two. With 44.1 kHz samplerate the
driver has to do lots of buffering to emulate the changing frame fill
which leads to masses of latency. For example, using 44.1 kHz on I
never got the old Quattro running with anything less than 3 periods
each with size 2024. Using 48 kHz samplerate this can be much lower.
In fact with my current USB card, I can gow as low as "-n 3 -p 256"

Just try it, you will see yourself.

 Frank Barknecht                               _ ______footils.org__

More information about the Pd-list mailing list