[ardour-users] Ardour and Latency Handling

Jan Depner eviltwin69 at cableone.net
Sun Apr 30 06:47:52 PDT 2006

On Sun, 2006-04-30 at 14:22 +0930, Andrew Johnston wrote:
> Hello,
> 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.

    I use a DSP2000 C-Port (envy24 chipset).  Since it has hardware
monitoring I always set my frames/period to 2048 so my latency is up
around 100 msec.  The only reason I would need to lower that is if I
needed to do software monitoring (so I could hear effects while
recording).  I haven't had any sync issues in the last couple of years.
In the options editor I have set hardware monitoring, positional
sync=internal, JACK time master.  I'm not sure why you would be having
these problems.  I would immediately suspect the click track.  One of
the tests I did when I was having problems with sync was to record hand
claps and then try to record a second track in sync at different
frames/period.  Doing this removes any possibility that the click track
is doing something weird.

Jan 'Evil Twin' Depner
The Fuzzy Dice

"As we enjoy great advantages from the invention of others, we should be 
glad of an opportunity to serve others by any invention of ours, and 
this we should do freely and generously."

Benjamin Franklin, on declining patents offered by the governor of 
Pennsylvania for his "Pennsylvania Fireplace", c. 1744

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