Re: [LAU] [Bulk] Re: [Qtractor-devel] [Fwd: Re: ; ) Was - Re: Session management with NSM]

On 2014-09-05 02:32, Kazakore wrote:
> On 05/09/14 03:56, Rui Nuno Capela wrote:
>> On 09/04/2014 10:34 PM, Ralf Mardorf wrote:
>>>
>>> This year You record an audio track with an I+O latency of 10.7 ms.
>>> Two year later you want to restore this session, but you don't
>>> remember
>>> the jackd settings you used. Originally audio and MIDI tracks were in
>>> sync, when you used 10.7 ms I+O latency. Within the years you got new
>>> hardware, you don't remember what latency you once used and starts
>>> jackd
>>> with a lower I+O latency. Nothing bad would happen for Ardour users,
>>> but
>>> a Qtractor user would run into sync issues. Am I mistaken?
>>>
>>
>> i really don't get why it would have worse or better sync depending on
>> jackd latency settings. please forgive me, but i don't see it directly
>> related to the case of audio vs. midi sync...
>>
>> though, in the special case that comes to mind, iif the alsa-midi
>> timer is slaved to a pcm sound-device, as against to the system or
>> hires timer for instance, you probably will get it different whether
>> running on disparate buffer-sizes, periods and/or sample-rates, that's
>> for granted--well, if you change the sample-rate across sessions you
>> will get prompted to convert into a brand new and different session
>> anyhow ;)
>>
>> byee
> Huh??
>
> So you have audio coming from the PC and MIDI going out to external
> sound generating MIDI devices and you don't see how output latency
> from the computer can affect the timing sync between sound from the
> computer and sound from the audio modules??? Surely even a blind
> wombat could see that! Unless there is some magic in Jack/AlsaMIDI
> which automagically delays the MIDI by the same as the output buffer
> settings of Jack. Then some might also want to add a fixed delay value
> to take into account the hardware delay (propagation time) but I think
> we really are getting a bit complex now!
>

re. external midi equipment, probably yes, that might be pertinent,
but...

my point was about audio and midi sync within qtractor (the sequencer)
internally. once midi gets out of the sequencer or even of the machine,
then i doubt one can ever compensate effectively for the delay, drift or
jitter that will be always present, no mater how small but orthogonal to
jackd buffer-size, periods or sample-rate, whatever, and sure matters to
a perfect sync. i doubt the output latency of the in-machine jack-audio
graph might be any significant or functional to that goal.

> Although I very much doubt anybody would be able to hear the
> difference if you're only talking a couple of ms and have different
> sounds both internally and externally (same sounds would cause comb
> filtering and eventually echo once latency became high enough.)
>

exactly :)

> But this is true for ALL audio coming out of the sequencer, whether
> you recorded it or it's from a sample-pack or a soft-synth etc etc.
>
> tl/dr: All that is really needed is an option to delay MIDI signals by
> the amount of the audio output buffer (plus you could add the optional
> hardware delay in settings if you really wished). This should bring
> output of both audio and MIDI sounds as close to sync as is possible,
> with the real-world systems being as imperfect as they are.
>

cheers

-- 
rncbc aka. Rui Nuno Capela
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