On 19 Oct 2016, at 10:20, Roman Haefeli <reduzent@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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