Re: [Jack-Devel] need a little help with jack_midi_latency_test

On Mon, Apr 11, 2011 at 8:56 PM, Devin Anderson
<[hidden]> wrote:

>> /usr/local/bin/jackd -t2000 -Xalsarawmidi -dalsa -dhw:0 -r44100 -p2048 -n2
>> -i2 -zt
>>
>> jack_midi_latency_test -m 3 -s 8192 -t 5 "system:1-1 Lexicon Lambda 1 out"
>> "system:1-1 Lexicon Lambda 1 in"
>
> A test with these parameters will take more than a couple minutes.

In asynchronous mode, with your period size set to 2048 and your frame
rate set to 44100, your in port latency will be around 46.5 ms, and
your out port latency will be around 93 ms.  If you add the two
together and multiply by 8192, you have a little over 19 minutes.

The reason this takes as long as it does is because the MIDI hardware
driver wants to align MIDI messages with audio so that your external
devices sync with JACK.  IOW, if you send a MIDI note on message to a
JACK soft-synth and a hardware synth, the notes should sound like they
occur at the same time.  If you do this with an ALSA port that isn't
wrapped with a JACK MIDI driver, the hardware synth will send out
audio for the note before the soft-synth's audio gets to whatever
audio interface you're using.

-- 
Devin Anderson
devin (at) charityfinders (dot) com

CharityFinders - http://www.charityfinders.com/
synthclone - http://synthclone.googlecode.com/

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