[Jack-Devel] questions about latency ranges

[Markus Grabner]

Am Samstag, 18. November 2017, 21:55:14 CET schrieb Xavier Mendez:
> El 18/11/17 a les 00:50, Markus Grabner ha escrit:
> > I vote for adding these tools to the Jack example clients. What do you
> > think about this?
> 
> It'd be nice if they also supported synchronizing MIDI ports, but that's
> TODO for now. For the rest, IMO they're pretty much ready to go.
I agree, MIDI would be nice to have, but the tools would be a useful addition 
even without MIDI support. Any opinions of other Jack developers on this?

> > BTW, one question regarding the "coefficient" parameter: I thought this
> > should always be "1" (align to maximum latency), but didn't notice any
> > difference when leaving its default value 0.5 (align to center), both
> > variants gave correct results. How does this coefficient affect the
> > behaviour of your client?
> The coefficient has no effect when all ports' input latency has the same
> minimum and maximum (i.e. one port [ 337 337 ] and the other [ 867 867
> ]). That's expected most of the time.
> 
> If one port had [ 523 1024 ] latency you'd probably be doing it wrong,
> but jack_lsync still has to deal with it, and that's what the parameter
> is for. If coefficient was 0, lsync would assume 523 latency when
> calculating the delays to apply, if it's 1 it'll assume 1024, and if
> it's the default it'll just take the mean of min & max, and assume 773.
> 
> So it's only there for those strange cases that should ideally never happen.
Ok, a device not knowing exactly its own latency is indeed odd. Thanks for the 
explanation!

> PS: If you want to use alsa_out or alsa_in, note this bug which may make
> them report wrong playback/capture latencies in some cases
> https://github.com/jackaudio/tools/pull/8
Thanks for the hint, but due to another self-citation :-) a while ago by Fons 
Adriaensen, I ended up using Zita-ajbridge (http://kokkinizita.linuxaudio.org/
linuxaudio/zita-ajbridge-doc/quickguide.html), which works very well for me.

	Kind regards,
		Markus