[ardour-users] Exporting with Hardware Inserts/Sends

[Wolfgang Woehl]

Andrew Johnston <andyandtaya at gmail.com>:

> issue is that I'm not sure exactly how long the latency is,
> JACK is set to 64 frames or 2.3 milliseconds, but ardour
> gives me a latency reading of half that...this is the same

Hi Andrew, your jackd is most likely set to use 2 x 64 frame 
buffers (-p64 -n2) which make up for p * n / samplerate 
seconds of round-trip latency (2.9 msecs @ 44.1k, 2.6 @ 48k). 
Ardour reports the one-way latency which is half here.

> for all settings on JACK, ardour gives half.  Maybe someone
> could explain the reason for this...so then assuming I go
> with JACK and it is 2.3ms, is that a real world figure, or
> do i just have to use my ears and trial and error to figure
> that one out?....cause there are other external factors
> such as the time taken to get to the mixer, be routed
> around the mixer and then back into the card.  This can all

Are you aware of jackd's -I and -O parameters? They let you 
specify the latency of an external signalpath like hardware 
inserts etc. You can measure it with jdelay (on Fons 
Adriaensen's page http://users.skynet.be/solaris/linuxaudio/)

Telling jackd about these numbers matters in the case of a 
client that does latency-compensation knee-deep in all the 
gory detail like Ardour does.

When I dug deeper into this once I started out thinking "I'm 
not perfect. Do I need perfect alignment really?" Only to 
realize a mis-aligned signal with bleed (drums) colours sound 
pretty fast, snare bleed 30 frames late makes a notable 
difference. Of course the bleed is already late but having 
another shift because of mis-alignment complicates things 
even more. So I need Ardour's perfect alignment.

Wolfgang