[FFmpeg-devel] [libav-devel] [PATCH] aacpsy: avoid norm_fac becoming NaN

[Michael Niedermayer]

On Sat, Apr 18, 2015 at 01:59:53PM +0200, Andreas Cadhalpun wrote:
> On 18.04.2015 04:40, Michael Niedermayer wrote:
> > On Sat, Apr 18, 2015 at 12:55:08AM +0200, Andreas Cadhalpun wrote:
> >> The problem is that minath is not the minimum, only close:
> >>     minath = ath(3410, ATH_ADD) = -5.24237967
> >>              ath(3407, ATH_ADD) = -5.24241638
> > 
> > the exact location of the minimum depends on teh "add" value
> > its around 3410 for add=0 and around 3407 for add=4
> 
> True.
> 
> > for fun, 3407.080774800152 is even closer than 3407 for add=4
> 
> Yes, but the ath function calculates with floats and thus is
> inaccurate enough that it doesn't matter if the input is 3407
> or 3407.1.
> 
> > but the "add" parameter should probably be user selectable
> 
> Currently ATH_ADD is a #define, but if that was made user selectable,
> one could approximate the position of the minimum:
>     minath = ath(3410 - 0.733 * ATH_ADD, ATH_ADD)
> 
> > also if you want to prevent coeffs[].ath from becoming negative then
> 
> That isn't strictly required, because 0 is a valid value and is just
> as bad as a negative one.

> But I assume the model works better, if it uses something closer to the
> minimum of the ath function.

thats more a question for claudio than me id say

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

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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