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

[Claudio Freire]

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.

>
>> But yeah, something that makes it closer, sure.
>>
>> I'd try to symbollicaly deriving the minimum if you really mean to
>> improve that (should be doable, it's all differentiable stuff).
>
> I actually derived the dependency of the minimum on ATH_ADD in first
> order around ATH_ADD = 0 (using sagemath).

ATH_ADD is defined as 4, that may make a significant difference
(changes a high-order term).