[ardour-dev] exact sample sync

Robin Gareus robin at gareus.org
Mon Jun 19 06:18:03 PDT 2006

>> ardour 0.99.2 (libardour 0.906.1): the output is exactly one
>> jack-buffer-size ahead in time!
> Check the setting for latency
> compensation on the track, in one of the context menus of the track
> header area.

latency compensation! There's the rub! ardour correctly takes the port
latencies into account. (on my system the 'alsa_pcm:playback_*' latency
is a buffersize..)

the easy workaround is to route the reference player 'tru ardour :)

> I assume there are no plugins.

no - i started with an new empty session.
but now that you mention it:

 - new session with two stereo tracks; set transport sync to jack
 - add some audio track on both tracks at the same position.
 - add DJ-EQ as pre-fader plugin to track 1
 - invert the polarity of track 2.

if you start playback while the DJ-EQ is bypassed, the tracks cancel
each other.

If you start playback with the DJ-EQ active, the tracks are shifted by 3
frames (the latency of the DJ-EQ) - and you hear some phased signal!

during playback the sync remains correct! Once playback is started it's
safe to toggle the bypass of the DJ-EQ, without breaking sync.

seeking behaves as a restart. (as does any action that kicks jack to
recalculate port latencies...)

can anyone reproduce this?


PS. a little digging reveals that track two is 3 frames early!

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