On 22.11.2015 14:26, Alexander E. Patrakov wrote:
22.11.2015 17:21, Georg Chini wrote:
The other big problem is that you cannot determine the number
of cycles you will need to correct the initial latency error because
this error is unknown before the first adjustment cycle.
You can circumvent this problem by sending zeros instead of the actual
data until you correct the initial latency error well enough. And,
because we are sending zeros, nobody cares if there are big frequency
steps. So one cycle is always enough to correct the initial latency
error once it is known, and then we can unmute the sound.
I do not understand what you are proposing. Are you saying we should
skip samples
until we are near the requested latency? So send no audio for at least
one adjust time?
That would mean that you have to reduce the adjust time drastically.
BTW, I did some experiments with shorter adjust times and could not see
a significant
improvement over the 1s interval.
When you calculate that safety margin you also have to consider
that the controller might overshoot, so you temporarily could
get less latency than you requested.
This is definitely impossible with the controller in PATCH 04/13
modified so that min_cycles is always 1. Indeed, by design, such
controller corrects exactly 100% of the latency error in one step,
without paying attention that it might be noticeable. And with
min_cycles > 1, it corrects less than 100% of the error, so cannot
make the situation any worse than it is. I.e. here overshoot would
mean correcting less than 0% or more than 100% of the error, and it
just can't happen.
In theory yes, but practice you are wrong here. It does overshoot
sometimes, especially
with long adjust times because we are taking measurements that have some
error.
Consider that the measured latency is 2 ms too long (this can easily
happen in the first cycles),
then you will correct 2 ms too much. With short latencies, even half a
millisecond might
be significant.
OTOH, the PI-controller that I am currently working on can indeed
overshoot. I think a good idea would be to detect situations where the
latency error is excessive or would be excessive during the next step,
and correct this situation with your controller with min_cycles = 1,
instead of my controller. That's, without paying attention to artifacts.
I will post this controller (and, as requested, perform measurements
with the trivial resampler) in the near future.
Thanks, please also test the patch I sent on Friday.
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