Subject: [linux-audio-user] some notes regarding sync (JACK, MTC) under Linux
From: Dave Phillips (dlphilp_AT_bright.net)
Date: Thu Dec 18 2003 - 15:53:05 EET
Greetings:
I followed the recent thread here regarding this issue but I was too
busy to contribute. Here are a few observations resulting from my own
tests :
Hydrogen works very nicely under JACK. However, when Song mode is
set to Loop the JACK transport works only on the first play through,
i.e., Hydrogen doesn't loop. Pattern mode looping is fine, but not Song
mode looping. Also, I'm losing the first beat when the transport starts.
Anyone else noticing that ?
Ecasound also works nicely with JACK but I haven't tested all the
transport functions yet. I just realized that ecasound should be able to
rewind to start under JACK. Kai, am I right about that ? Where can I
find a summary of ecasound's current JACK capability ?
MusE and Rosegarden don't yet work with the JACK transport, but
that's not news. However, I did sync MusE to external MTC and it worked
very nicely. I thought I had been able to do the same thing internally
with the ALSA virmidi module, but upon sober reflection it appears I was
smoking bad crack. Am I correct in assuming it's not possible to send
MTC over the virtual MIDI connection ?
Again not news: Ardour works nicely as a JACK master but it doesn't
seem to like being a slave (but who does ?). Also, am I correct to note
that Ardour doesn't respond to incoming MTC or MMC ? I'll have to check
that again...
The latest Hydrogen release notes state that MMC/MTC are
experimentally supported, but I don't see any switches for those
controls. Has anyone else tried utilizing MMC or MTC with the new Hydrogen ?
Qjackctl is very sweet (Thanks Rui!), but a rewind transport control
might be nice to see on it.
Finally, a non-sync issue (?) that I think has been reported before.
Sometimes the sound gets distorted while running an app under JACK (not
necessarily under the transport control). It cleans itself up after a
little time, but it's a Very Bad Thing to be happening. Instruments with
lower frequencies seem to trigger the distortion (bass drum, low toms,
etc. in Hydrogen). Has anyone else noticed and fixed this problem ? In a
similar vein, I tried recording Hydrogen to two channels in Ardour,
running Hydrogen as slave, Ardour as master. The first play-through of
the Song in Hydrogen records fine in Ardour, but then I get a terrible
distortion. I can supply a soundfile and screenshot that clearly
sounds/shows what's happening. Perhaps it's related to the first problem
above ?
System here is as follows:
800 MHz Duron w. 512 MB RAM
current PlanetCCRMA RH9 w. low-latency kernel
ALSA 1.0.0rc2
SBLive Value
Kudos to all the developers working on fastening their apps to the
JACK transport model. As joq stated this is one of the most impressive
aspects of the whole JACK schema, at least for the normal user.
Best regards,
== dp
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