[LAU] USB2 Audio, PreSonus Audiobox 1818VSL -- was: Sound Devices USBPre2, UAC2 status

[Fons Adriaensen]

On Wed, Jan 30, 2013 at 07:14:11PM +0100, Robin Gareus wrote:
 
> This works reliably; no x-runs:
>   jackd -d alsa -d hw:2 -r 48000 -p 64 -n 3
>   jack-delay measures: 403.949 frames    8.416 ms
> 
> 
> Occasional rare x-runs with
>   jackd --sync -d alsa -d hw:2 -r 48000 -p 64 -n 2
>   roundtrip latency: 274.945 frames    5.728 ms

That's odd. The difference should be one period, 64 frames.
But it is 129 frames.

> 
> Now we're closing in...
>   jackd --sync -d alsa -d hw:2 -r 48000 -p 32 -n 2
>   roundtrip latency:  175.953 frames    3.666 ms
> x-runs depend on system load. jack_capture still runs x-runs free for >
> 1 hour. Idle DSP load is only 5.6% with the CPU in low-power (1GHz). Yet
> jack_delay alone bumps DSP load up to 20%.

The % load for jack_delay shouldn't depend much on the period size,
it just processes period_size frames each time.

If it does there could be significant wakeup jitter - jack measures
the worst case load IIRC.

Ciao,

-- 
FA

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