[mythtv] AVSync2 Refinements

[Mark Spieth]

On 12/16/2019 4:21 PM, David Engel wrote:
> On Sat, Dec 14, 2019 at 03:00:24PM +0000, Mark Kendall wrote:
>> On Fri, 13 Dec 2019 at 18:21, Tim Pletcher <pletchtd at gmail.com> wrote:
>>>
>>>> I was able to do a little more testing today and figured out how to nicely parse the log playback,timestamp data into a comma-delimited file to enable me to look more closely at some real data.
>>>>
>>>> First, I found that a 0.4 gain and 0.9 filter as I initially proposed does work well.
>>>
>>> Apologies Mark.
>>>
>>> I just noticed you already committed the 0.04.  I don't mean to appear so indecisive on this :)   I think it is probably splitting hairs at this point as the control seems to work pretty good with either settings.
>> Tim
>>
>> No problem. I'm minded to go back to 0.4 as it generally seems a
>> little slow to respond at the moment.
> Count me firmly in the 0.4 camp.  I didn't see much difference with
> progressive content yesterday but did today with interlaced content.
> 0.04 takes noticably longer to settle down.
>
You can actually have a fast startup IIR (which is what it is) using a 
counter as the inverse of the feedback coeff and saturate it at the 
desired long term coeff value

i.e.

Y[n] = Y[n-1] * (1-1/c) + (1/c)*X[n]

c1 = 1 to K, K is where 1/K < 1/A, A is long term input coeff

c = min(c1, 1/A)

This assumes unity gain.

This gets you stable long term single pole filtering with fast startup.

HTH

MarkS