[Ffmpeg-devel] AAC decoder
Benjamin Larsson
banan
Wed Mar 22 10:46:54 CET 2006
Mike Melanson wrote:
> Benjamin Larsson wrote:
>
>> And the sine_short table should be a subset of sine_long.
>
>
> That seems intuitive, but I don't think it's true in this case.
> The short values are derived as:
>
> for odd values i in 1..127
> sine_value = sin(i * PI / 512)
>
> For long values:
>
> for odd values in 1..1023
> sine_value = sin(i * PI / 4096)
>
> In the short formula, you could multiply (i * PI / 512) by (8/8) to
> get the same denominator as in the long formula. But multiplying by 8
> would make the numerator even and thus the sine value would not occur
> in the long table.
You are right, the term (that you missed here) makes it impossible, but
I think that it would be possible to approximate the window by tweeking
the term abit to reduce the error. And you got the term wrong, it should
be 0.5.
>
> (I think.)
MvH
Benjamin Larsson
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