Subject: Re: [linux-audio-dev] Tutorial on Professional Audio GNU/Linux Tools
From: Maarten de Boer (mdeboer_AT_iua.upf.es)
Date: Wed Jul 14 2004 - 15:40:32 EEST
Hello,
aaron_AT_nquit.com wrote:
> And did you find RoseGarden and Ardour we're sync'd up tightly?
> I have yet to find them REALLY syncing really tightly....
>
> what distro are you on? what versions of the software? what hardware?
Sorry for not replying earlier. We wanted to do some tests first, and that
got delayed a little.
About syncing: first of all, we have been using JACK for the sync
mechanism. We also tried using MTC, but we could not get that to work.
Syncing seems to work okay, in the sense that things keep in sync over
time, but we had to adjust offsets to correct the initial sync.
We made some tests to get a more clear picture, and in fact we got
rather confused instead. I will just give you the results, without
trying to explain what happens. I am sure some of you will be able to
shed more light on these results. And maybe they can help
ardour/jack/rosegarden developers in some way or another
Test setup:
- jack configured at 44100 Hz, and we tried with 2 buffers of 2048 and
2 buffers of 4096
- A MIDI track in rosegarden4, with a beat at 120 BPM.
- MIDI output (USB MIDI-Sport 2x2) connected to an external MIDI module
- Audio output from the external MIDI module connected to an Emagic EMI
2|6 USB audio device.
- In Ardour, we create two tracks, one to record the audio from the MIDI
module, one to record the ardour click (jack loopback).
I know the buffersize of jack is very big, but for doing this test, the
larger audio latency makes things more obvious. Also, we have not been
able to use the EMI 2|6 with ALSA with a period smaller then 2048
without strange ticks. I should contact the ALSA list about this, but on
the other hand, this device is a horrible piece of overpriced plastic
crap with lousy connectors, that I would not recommend to anyone even with
smaller buffer-sizes...
Results:
About the recorded (jack loopback) ardour-click: Strangly enough, the
first click occurs before time=0. Looking at the second click, which
should be at 0.5 sec = 22050 frames, we can see how much the clicks
are ahead of time:
- jack_AT_2x2048: click at 20002 frames; offset = -2048 frames
- jack_AT_2x4096: click at 17954 frames; offset = -4096 frames
Indeed: exactly 1 buffer. Strange, isn't it?
More complicated is the recorded MIDI click. These occur even BEFORE the
recorded jack clicks. Now, I am not 100% certain if maybe we set the
delay of the MIDI track in Rosegarden (I don't have access to the
machine right now, but I will tell you as soon as I do), but I don't
think so, and even so, the results are strange.
- jack_AT_2x2048: click at 18450 frames; offset = -3600 frames
- jack_AT_2x4096: click at 14100 frames; offset = -7950 frames
I don't see the relation between those numbers...
Versions used:
Hardware
* Emagic EMI 2|6
* USB Midi-Sport 2x2 (in a Steinberg box)
* Acer Travelmate 800
Sofware
* Kernel 2.4.26
- patches: Preemptive 2.4.26-pre5-1, RTC 2.4.25, 2.4.25-low-latency
* Alsa 1.0.5a
* Jack 0.98.1
* Ardour 0.9 Beta 17.1 (Ardour/gtk 0.520.9, libardour 0.820.1)
* Rosegarden4 0.98
Maarten
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