[LAD] Jack MTC/MMC slaving

Paul Davis paul at linuxaudiosystems.com
Mon Nov 24 21:39:05 UTC 2008

On Mon, 2008-11-24 at 21:40 +0100, Ralf Mardorf wrote:
> Alex Montgomery wrote:
> >
> >     that said, i do think its a little odd to make this utility connect to
> >     JACK MIDI. any JACK MIDI client sending MMC to do transport control is
> >     just being stupid - it can control the transport directly. the
> >     interesting cases all involve the MMC source outside the computer,
> >     which
> >     makes using ALSA MIDI directly a bit more sensible (IMHO).
> >
> >
> > Wow, really? I thought that JACK (via ALSA on Linux, but this is
> > implementation dependent) supported access to external ports anyway.
> > We were going to switch to JACK midi because it is theoretically more
> > portable (to OS X, say) and more JACK compliant (which a JACK
> > transport app should be), without adding any dependencies (obviously
> > we are already using the JACK libraries since jackctlmmc is a JACK
> > client.).  I assumed that the only repercussion of switching to JACK
> > midi would be that the user would have to make the connection to the
> > external ports using a JACK controller instead of alsa utilities like
> > aconnect. In the case of people using an app like QJackctl, the
> > application would simply hop to the JACK tab instead of the ALSA tab.
> > Is that not true? Are there other complications that could stop users
> > from connecting to external midi devices?
> >
> > It's good news if ALSA is the better choice; it's how the code is
> > currently written anyway.
> >  
> > -- Alex
> The jackd -dalsa -X option seems to make clients available for both
> QjackCtl tabs, but e.g. Qtractor's connection GUI only shows ALSA.

Not relevant, because using Qtractor as the MMC source is silly :)

the point is that yes, JACK provides bridges to the outside world (via
phsyical MIDI ports), but these are more "expensive" than using ALSA. if
the goal is to get the incoming data into jackmmcctl ASAP, then ALSA (or
other native MIDI layer) makes more sense.

if you want an idea about common MIDI port APIs (including JACK, ALSA
and CoreMIDI and even OSS) check libs/midi++ in the ardour tree).

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