[PD] Latency compensation

[Miller Puckette]

This has been on my mind a long time - Pd really should provide a way to
query the audio devices to whatever accuracy the underling system is
capable of giving it.

I believe portaudio already does this - Pd can just piggyback on that and/or
follow the portaudio model for whatever specialized I/O APIs it talks to.

cheers
Miller

On Wed, Oct 19, 2016 at 01:42:25PM +0200, Simon Iten wrote:
> 
> > On 19 Oct 2016, at 10:20, Roman Haefeli <reduzent at gmail.com> wrote:
> > 
> > [replying to pd-list]
> > 
> > Hi Simon
> > 
> > On Wed, 2016-10-12 at 09:30 +0200, Simon Iten wrote:
> >> it would very much surprise me, if pd could do that in a generic way
> >> on all platforms. even daws or live struggle to do this *right* on
> >> different systems. 
> > 
> > I'm not sure it's totally impossible. With jack, the latency is
> > dependent on jackd's settings and I don't whether Pd has a change to
> > know those. With ALSA, everything you need to know to calculate the
> > latency Pd already knows.
> but there is also an ADC and DAC latency, is jack or alsa aware of those as well? i believe typical adc/dac conversion can take up to 1.5ms…
> 
> > 
> >> why don't  you patch a little tester app that sends some generated
> >> sounds, preferably with very clear attack, out and record this back
> >> in. that way you can measure the (roundtrip) latency of the whole
> >> system.
> > 
> > Of course, that is a way. "Knowing" the latency instead of "measuring"
> > it would be so nice, though.
> of course knowing is better than measuring :)
> 
> i think it is easy enough to measure roundtrip latency, it is harder to measure just “output” latency.
> 
> 
> > 
> >> with a click track and a good musician that plays with it (that you
> >> record) you should be able to align generated sounds and live
> >> recorded material. this is how we do it in the studio if necessary :)
> >> but it is far from an automated process...
> > 
> > To make things at least a bit more feasible, I make the measured or
> > calculated latency a configuration parameter, so that when you fire Pd
> > up the next time with the same setup, the patch remembers the latency.
> that sounds reasonable.
> > 
> > Roman
> > 
> > 
> >> Am Sonntag, 9. Oktober 2016 schrieb Roman Haefeli :
> >>> Hi all, 
> >>> 
> >>> I'm currently investigating audio latency compensation in Pd. The
> >>> goal
> >>> is for recorded audio to align well with generated sounds timing-
> >>> wise.
> >>> I'm wondering now what methods people already have employed in
> >>> order to
> >>> achieve that goal.
> >>> 
> >>> So far, I was able to find the formulas to calculate the correct
> >>> latency when using ALSA and JACK audio back-ends as long as the
> >>> paramaters 'Delay(msec)' and 'Block size' for ALSA, respectively
> >>> 'Frames/period' and 'Periods/buffer' for JACK are known. Currently,
> >>> this approach works, but requires me to tell the latency
> >>> compensation
> >>> calculator what driver I'm using and what the current settings are.
> >>> Also, it yet only works on Linux, but not with any other drivers
> >>> like
> >>> CoreAudio, ASIO, etc.
> >>> 
> >>> How can I achieve correct latency compensation reliably on any
> >>> platform? Is there some more generic way?
> >>> 
> >>> I'm also looking at IEM's mediasettings library, hoping it would
> >>> deliver the required information to calculate latency. The
> >>> README.txt
> >>> says 'get/set Audio and MIDI settings within Pd', but I wasn't able
> >>> to
> >>> find a way to _get_ current settings other than 'advance 100',
> >>> which
> >>> probably refers to 'Delay(msec)' set to '100'. But still, if it
> >>> would
> >>> give all Pd audio settings, how would it know about current jackd
> >>> settings?
> >>> 
> >>> Roman
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