[FFmpeg-devel] [Issue 664] [PATCH] Fix AAC PNS Scaling

[Michael Niedermayer]

On Tue, Oct 07, 2008 at 01:48:40PM -0400, Alex Converse wrote:
> On Tue, Oct 7, 2008 at 1:01 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Mon, Oct 06, 2008 at 11:30:56PM -0400, Alex Converse wrote:
[...]
> >>
> >>
> >> >
> >> >>
> >> >> >
> >> >> >>
> >> >> >> >
> >> >> >> >>
> >> >> >> >> However with this patch there appears to be no audible difference
> >> >> >> >> between the approaches.
> >> >> >> >
> >> >> >> >> I don't know the ideal mean energy so I'm
> >> >> >> >> using the sample mean energy for 1024 iterations of the LCG.
> >> >> >> >
> >> >> >> > i assume cpu cycles got more expensive if people can only spare a few
> >> >> >> > thousand
> >> >> >> >
> >> >> >>
> >> >> >> How many do you propose then? I tried running it over the whole period
> >> >> >> and the result seemed low, I think it's a classic case of adding too
> >> >> >> many equal size floating point values.
> >> >> >
> >> >> > real mathematicans tend not to use floats that are bound to rounding errors
> >> >> >
> >> >> > try:
> >> >> > for(i=min; i<=max; i++){
> >> >> >    uint64_t a= i*i;
> >> >> >    var += a;
> >> >> >    if(var < a){
> >> >> >            var2++;
> >> >> >    }
> >> >> > }
> >> >> >
> >> >>
> >> >> That will only hold 5 or 6 big values 2^64/((2^31)^2) = 4.
> >> >
> >> > read the code again please, especially var2
> >> > also, just to make sure you have the types correct
> >> >
> >> > int min= -(1<<31)+1;
> >> > int max=  (1<<31)-1;
> >> > int64_t i;
> >> > uint64_t var=0;
> >> > uint64_t var2=0;
> >> >
> >>
> >> Why are we leaving out (int)0x80000000?
> >
> > because otherwise the mean would be -0.5.
> 
> But isn't it in the output space? 

yes, approximately once every 2^32 values


> We're trying to find the energy of
> one period of the LCG no?

yes


> If we are going to ignore it shouldn't the
> LCG be written to explicitly reject it?

not really, no


> And adding logic to explictly
> reject it seems nutty for such a small deviation in the mean.

> It has
> far more significance in energy.

.0000000008065490087349327716857165436802471967650737954699499861349...
vs.
.0000000008065490090166167590309147460339081318382480645839026837603...
for the normalization constants

iam not sure how you can call that "far more significance" on one hand and
pretend that skiping per band normalization would be ok OTOH.


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato
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