[Ardour-Users] Sync between internal and external sources

Mark Knecht markknecht at gmail.com
Wed Jan 21 07:21:18 PST 2009

On Wed, Jan 21, 2009 at 6:50 AM, Mark Greenwood <fatgerman at ntlworld.com> wrote:
> I've thought very hard about this question and now my head hurts.. I'm
> wondering about how, if at all, Jack/Ardour ensures that all sound sources
> stay in sync.
> Let's assume for the moment that I'm capable of playing an instrument such
> that I'm in perfect sync with a drumbeat.. (this is a big assumption but we
> have to start somewhere.. )
> I'm using Jack. I have Ardour set to JACK Time Master. I have Hydrogen set
> up to sync to Jack and play a beat. I have Ardour set up to record me
> playing the bass through my soundcard. I press the Play button - Hydrogen
> starts playing, I start playing, Ardour starts recording me.
> Question 1 : When I play back my recording of me playing bass, and have
> Hydrogen playing along - are they in sync? Or is my bass part now delayed
> relative to Hydrogen by a value equal to the latency of my sound card?
> Question 2 : When, at a later date, I mix down by recording the output from
> Hydrogen into tracks in Ardour, does the sync change?
> I ask because it sounds like I'm not in sync with my drums but I don't know
> if it's me.... It might be that the answer to this is so obvious that I
> can't see it for looking. I do know I can't see it... please help..
> Mark

Jack itself really doesn't do anything except use a clock from one of
the sound cards. We have to ensure that every sound card is using the
same clock. By using the right external clock and specifically hooking
it up to all sound cards in all systems they all stay in sync.

It's possible to use a sound card as the master clock if it has the
right outputs. Those outputs *might* be spdif, word clock or ADAT.
(Maybe others but those are the ones I've used) you have to enable the
output to send the clock and then have to enable the other cards to
use that clock instead of its interna crystal.

Hope this helps,

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