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

[Michael Niedermayer]

On Mon, Apr 20, 2015 at 09:07:14PM -0300, Claudio Freire wrote:
> On Mon, Apr 20, 2015 at 8:59 PM, Claudio Freire <klaussfreire at gmail.com> wrote:
> > On Mon, Apr 20, 2015 at 8:32 PM, Andreas Cadhalpun
> > <andreas.cadhalpun at googlemail.com> wrote:
> >>>>> The long version:
> >>>>>
> >>>>> ath should approximate the shape of the absolute hearing threshold, so
> >>>>> yes, it's best if it really uses the minimum, since that will prevent
> >>>>> clipping of the ath curve and result in a more accurate threshold
> >>>>> computation.
> >>>>
> >>>> So you agree with my patch fixing minath?
> >>>> Or would you prefer a version with:
> >>>>     minath = ath(3410 - 0.733 * ATH_ADD, ATH_ADD)
> >>>
> >>> Well, that's not really closer to the minimum (a few tests with gnuplot say).
> >>
> >> Are you sure your plots were done correctly?
> >> Because I'm quite sure this is the correct first order approximation
> >> of the minimum.
> >>
> >> For ATH_ADD = 4 this gives 3407.068, which is quite close to Michael's value
> >> (3407.080774800152).
> >
> > I checked the formula several times, but still, I could have made a mistake.
> 
> 
> This is what I did if you want to check it out (maybe you spot the mistake)
> 
> gnuplot> ath(f,a) = _ath(f/1000.0, a)
> gnuplot> _ath(f,a) = 3.64 * f**(-0.8) - 6.8 * exp(-0.6 * (f-3.4) *
> (f-3.4)) + 6.0 * exp(-0.15 * (f-8.7) * (f-8.7)) + (0.6 + 0.04 * a) *
> 0.001 * f * f * f
          ^^^^^^^^^^
missing * f

also IIRC gnuplot is just double precission
depending on how many decimal places one wants to calculate this can
become a limitation

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

I do not agree with what you have to say, but I'll defend to the death your
right to say it. -- Voltaire
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