[FFmpeg-devel] [Jack-Devel] [PATCH] libavdevice: JACK demuxer

Michael Niedermayer michaelni
Wed Mar 4 17:06:08 CET 2009

On Wed, Mar 04, 2009 at 12:34:08PM +0100, Olivier Guilyardi wrote:
> Michael, Fons has made the following answer on jack-devel to your comments about
> his paper:
> Fons Adriaensen wrote:
> > On Tue, Mar 03, 2009 at 09:18:39PM +0100, Olivier Guilyardi wrote:

> > 
> >>> Besides strictly speaking the optimal values of these parameters are non
> >>> constant. To see why just consider that the exact samplingrate is initially
> >>> not known exactly and has to be estimated first
> > 
> > Filter parameters do not in any way depend on the
> > (small) error on the sample rate. Again, using 
> > critical damping will ensure that the filter will
> > adapt to a sample rate error as fast as can be done
> > given the bandwidth.

well, the filter will take the first system time it gets as its
best estimate and then "add" future times slowly into this to
that is it weights the first sample very differently than the following
ones, this is clearly not optimal.
or in other words the noisyness or call it accuracy of its internal state
will be very poor after the first sampele while after a hundread it will
be better. The filter though will add samples in IIR fashion while ignoring

its a little like trying to find the average of 100 values and to do this
a= value[0]
for(i=0; i<100; i++)
    a+= (value[i]-a)*0.01

> > 
> >>> also the authors of the paper test the filter meassuring
> >>> its jitter, i dont see in how far this is meassuring the
> >>> quality of the filter,
> > 
> > What do you mean by 'quality' ? 

the sum of squared errors between the true sampling times and the output
of the filter.


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire
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