[FFmpeg-user] aevalsrc question

[Adam Puckett]

On 12/20/16, Muhammad Faiz <mfcc64 at gmail.com> wrote:
> On 12/20/16, Adam Puckett <signalsender103 at gmail.com> wrote:
>> On 12/19/16, Nicolas George <george at nsup.org> wrote:
>>> Oh, good catch. I should have remembered this task needed a primitive
>>> function, not just a multiplication.
>>>
>>> Regards,
>>>
>>> --
>>>   Nicolas George
>>>
>> What do I need to do to make the formula right?
>
> Just do the reverse.
> Given freq(t) = 262 * 2^(t/10)
> w(t) = 2*PI * 262 * 2^(t/10)
> ph(t) = integral of w(t) dt
>       = 2*PI * 262 * 10/log(2) * 2^(t/10) + arbitrary constant
>
> Thx.
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Thanks, that worked! But the question is: why? I don't quite
understand why I had to put in the log(2) expression.

On a related note, I've looked at a formula that does  linear
interpolation (one of the example scripts for Praat
(http://praat.org/)), and there is a division by 2 in the script; is
this for a similar reason? (For arbitrary targeted frequencies, I'm
assuming I would have to use a log(highestfreq/lowestfreq) in place of
the log(2)?)

Thanks