[LAD] [64studio-users] MIDI jitter

[Niels Mayer]

On Mon, Jul 5, 2010 at 12:16 AM, Clemens Ladisch <clemens at ladisch.de> wrote:
> 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.

Note that for kernel 2.6.32.14-127.fc12.x86_64, and for
## snd-card-3 snd-usb-audio ## --> Emagic MT4
## alias snd-card-5 snd-usb-audio ## --> Roland UM-2
##
## amixer -c 5 --> returns nothing
## amixer -c 3 --> returns nothing

Maybe the feature will be present in fedora 13?

> 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.)

Here's results for the Roland UM-2 with the argument suggested:

## sudo alsa-midi-latency-test -w 1 -r -R -i 36:0 -o 36:0
> alsa-midi-latency-test 0.0.3
> set_realtime_priority(SCHED_FIFO, 99).. done.
> clock resolution: 0.000000001 s
> interval between measurements: 1.000 .. 2.000 ms

Test1)

  2.1 -  2.2 ms:      488 ########################
  2.2 -  2.3 ms:      961 ###############################################
  2.3 -  2.4 ms:     1023 ##################################################
  2.4 -  2.5 ms:     1030 ##################################################
  2.5 -  2.6 ms:      996 ################################################
  2.6 -  2.7 ms:      971 ###############################################
  2.7 -  2.8 ms:      952 ##############################################
  2.8 -  2.9 ms:     1013 #################################################
  2.9 -  3.0 ms:     1025 ##################################################
  3.0 -  3.1 ms:     1013 #################################################
  3.1 -  3.2 ms:      518 #########################
  3.2 -  3.3 ms:        6 #
  3.3 -  3.4 ms:        1 #
...
  3.5 -  3.6 ms:        1 #
  3.6 -  3.7 ms:        1 #
...
  3.8 -  3.9 ms:        1 #

 best latency was 2.08 ms
 worst latency was 3.84 ms, which is great.
..........................................

Test2)
...
  2.1 -  2.2 ms:      479 #######################
  2.2 -  2.3 ms:      944 #############################################
  2.3 -  2.4 ms:     1034 #################################################
  2.4 -  2.5 ms:     1012 ################################################
  2.5 -  2.6 ms:     1006 ################################################
  2.6 -  2.7 ms:      985 ###############################################
  2.7 -  2.8 ms:      913 ############################################
  2.8 -  2.9 ms:     1046 ##################################################
  2.9 -  3.0 ms:     1021 #################################################
  3.0 -  3.1 ms:     1011 ################################################
  3.1 -  3.2 ms:      543 ##########################
  3.2 -  3.3 ms:        3 #
...
  3.4 -  3.5 ms:        2 #
  3.5 -  3.6 ms:        1 #

 best latency was 2.07 ms
 worst latency was 3.55 ms, which is great.
............................

Last time, with "-w 20":

Test1)
 best latency was 2.03 ms
 worst latency was 3.19 ms, which is great.

Test2)
 best latency was 2.07 ms
 worst latency was 3.11 ms, which is great.

-- Niels
http://nielsmayer.com