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

Robin Gareus robin at gareus.org
Wed Jan 30 18:14:11 UTC 2013

On 01/27/2013 03:09 AM, drew Roberts wrote:
> What sort of latency can you get down to?

Hi Drew,

On linux 3.2.0-4-rt-686-pae (debian) with ondemand governor and old
gnome2 on a Thinkpad X60s. jackdmp 1.9.10 (recent git)

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

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%.

At 96kHZ the minimum period is 64 fpp. The lowest setting is not what I
would take on stage but it works. jack_delay alone is causing 35% DSP
load. ondemand gov switches between 1GHz and 1.67 GHz, no x-runs in the
last 2 mins, but they'll come..
  jackd --sync -d alsa -d hw:2 -r 96000 -p 64 -n 2
  roundtrip latency: 276.273 frames    2.878 ms


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