[ardour-users] Ardour and Latency Handling

Andrew Johnston andyandtaya at gmail.com
Sat Apr 29 21:52:41 PDT 2006

I would like to bring up an issue that has caused confusion for me, and
probably for others as well.  I (since starting to use ardour) was under the
assumption that when using ardour it is of most benefit to have the lowest
latency (periods in jack) possible for ones system.  While talking on the
#ardour irc channel last night, I was informed that for standard multitrack
recording and overdubbing, latency does not factor into the situation if not
using softsynths, or live dsp performing as ardour handles the latency
internally, and syncs all the tracks to line up with each other, based on
the latencies reported to it by jack and by the ladspa plugins.  So for
example if the latency was 100ms then when one went track guitars over the
drums, ardour would simply adjust to make sure that the guitars lined up
with the recorded material, and not 100ms later than the recorded material.
This all seems to make perfect sense, however I don't believe it is the
case.  I did some testing and found that the higher I set the period in
Jack, the more out of time the tracks were.  Adjusting the option by right
clicking on the track and changing from 'align with recorderd material' and
'align to capture time' made no difference.
I will explain how I tested for the problem.
I have an RME HDSP9652 connected via adat to a Behringer DDX3216.  I routed
the click track out channel one, and on my mixer rerouted channel one input
back out to channel 2.  I then recorded channel 2 in ardour and therefore
got the click track recording at the same time as playing.  I then played
back from the beginning with click track still enabled.  At -p 64 there was
no delay between the two.  At -p 1024 there was a noticeable delay.  I went
one step further and switched off the click, and used the exisiting recorded
material (now it's own click track) and routed it out and back in on another
track.  I returned the same results, and regardless of the toggling the
alignment options, there was no difference.  This leads me to believe that
in fact ardour does not handle latency internally and therefore it is of
upmost importance to have low latency to get accurate, in time recordings,
or that there is a bug in ardour, or that I am doing something wrong =).
Please note I do not use software monitoring, and I have made sure that
hardware monitoring is the only thing selected in ardour options.

I would like to get down to the bottom of this, as the person I was talking
to on #ardour said he is aware that everyone thinks low latency is really
important, but in reality most of us don't need it, only a select few.  If
that is the case it is good news for a lot of people busting their buts to
get their system tweaked to the extreme, but if it isn't then it is vitally
important that we help people in achieving good low latency performace.

I'd appreciate any comments.

Andy J =)
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