[LAD] Jack MTC/MMC slaving

Alex Montgomery apmontgomery at gmail.com
Mon Nov 10 15:01:29 UTC 2008

Hello and thanks for the response :)
I've inlined my responses below:

JACK does not and will not support varispeed. Therefore slaving to MTC
> is going to be pretty limited. MMC also sends some speed commands that
> could not be supported by JACK.

I understand, but I think limited MTC support is better than nothing. That
being said, I don't think it's necessary to change JACK for this purpose,
jackctlmmc's approach of being a jack compliant app that can drive JACK
transport by listening to MMC signals seems like an elegant approach.

> > There's a small program called jackctlmmc that seems to do want I
> > want, but it's a bit limited (seems pretty hardcoded) and I think that
> > such a desirable feature should be integrated into a more widely used
> > program. Any thoughts?
> what does "hardcoded" mean?

I made that comment in ignorance. I didn't see a place in the code where you
could choose which MIDI device/port you were reading from, so I assumed that
it just took the first registered one or hardcoded (specified in code
instead of parameters passed into the program) a particular port. On closer
inspection, it seems that you either have to patch a midi port to the
application via JACK so it knows which one to read from, or it just reads
from all alsa midi signals, either of which is perfectly reasonable. I'm new
to the JACK and ALSA APIs, and I'm still waiting on a cable order to get my
8-track to talk to my PC, so I can't really test to see how this stuff

Currently jackctlmmc supports the "play", "stop", and "rewind" messages from
MMC, and I'm going to play with the code to see if I can add support for
"locate" using jack_transport_locate() so that players can have a primitive
seek-to type of function. I think that even this limited subset of MMC
functionality is very desirable for linux audio engineers. I just want to be
able to sit at my 8-track with my guitar and play/stop, rewind, and maybe
seek around without having to keep clicking a mouse on a JACK app.

I'm surprised that jackctlmmc doesn't seem to be that widely used (I can't
find any packages for it in the major linux distros, and it only seems to be
distributed via source code) when it provides such useful functionality. I'd
love to see it's functionality integrated into a GUI app like QJackCtl
(which already has JACK transport buttons for play, rewind, fast-forward)
instead of being a console application, but that's a subject for another

Thanks for your reply,
-- Alex
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.linuxaudio.org/pipermail/linux-audio-dev/attachments/20081110/cd8a1c04/attachment.html>

More information about the Linux-audio-dev mailing list