[LAD] [64studio-users] MIDI jitter

[Clemens Ladisch]

Niels Mayer wrote:
> Here's the new results with "-w 20" (nb: "-w" == "-w 0")
> 
>> A) Edirol UM-2
> 
>  best latency was 2.07 ms
>  worst latency was 3.11 ms, which is great.

As long we're optimizing for benchmarks:  In recent enough kernel
versions, Roland (Edirol/BOSS) USB MIDI devices have a mixer control
"MIDI Input Mode" (the same as the "Light Load" checkbox in the Windows
driver) which doesn't have much effect in practice but can improve
benchmark behaviour.

For bulk transfers (used by Roland devices in "High Load" mode, and
always by all other devices), the UHCI driver has a feature called FSBR
(full-speed bandwidth reclamation) which makes the controller poll the
device continuously instead of every 1 ms, as long as new input is
available every 10 ms.  So to get better benchmark numbers, use "-w 1"
instead of "-w 20".  (If your music doesn't have new notes every 10 ms,
this isn't very realistic, but it can improve latency between the
consecutive notes of a chord.)


Regards,
Clemens