[FFmpeg-devel] [PATCH] lavc/lpc: exploit even symmetry of window function

Ganesh Ajjanagadde gajjanag at gmail.com
Fri Mar 11 03:43:52 CET 2016

On Thu, Mar 10, 2016 at 11:21 AM, Rostislav Pehlivanov
<atomnuker at gmail.com> wrote:
> On 10 March 2016 at 01:55, Ganesh Ajjanagadde <gajjanag at gmail.com> wrote:
>> In fact, I personally have no idea why it is absolutely critical that
>> a Hamming window is used, see 0cfdaf45c4 where Welch was used
>> previously. At a first glance I think one can find a window that works
>> and avoids libm, e.g Parzen or other polynomial windows.
>> Rostislav, any thoughts?
> Yes, though experiments the Hamming window was determined to work the best
> with the TNS system. The Welch window was far too wide and caused
> artifacts. The Prazen window seems too focused to let the LPC algorithm do
> its job on correctly giving proper coefficients near the ends of the
> window. The LPC coefficients are used by the decoder to shape the spectral
> coefficients right before iDCT and after everything else, so it has big
> implications on the quality.
> I'll experiment with other types of windows, but I think the performance
> penalty here is really worth it.

Thanks for clarifying. Agree it is probably not worth it. Pushed, thanks.

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