[flac-dev] [PATCH] New apodization functions

Erik de Castro Lopo mle+la at mega-nerd.com
Mon Sep 22 01:24:11 PDT 2014

Martijn van Beurden wrote:

> Hi,
> > If I understand this correctly, these new apodization functions only
> > affect compression and that files compressed with these new functions
> > will still decode correctly with older versions of the FLAC decoder.
> >
> > Is that right?
> Yes, that is correct. These functions are used to window the 
> audiodata, but only for the predictor stage. What these new 
> function enable, practically speaking, is using only part of the 
> signal to generate a predictor. My theory is that this helps 
> because short transients introduce noise into the predictor. The 
> predictor becomes very good at prediciting one part of the 
> signal, instead of mediocre for the whole block.
> For more information on the whole window-thing, it might be a 
> good idea to see this hydrogenaudio-post by Josh himself: 
> http://www.hydrogenaud.io/forums/index.php?showtopic=44229
> One thing to note is that this patch only affects the encoder 
> stage that evaluates various possible predictors, not the actual 
> coding stage.

Great, thanks for the explanation.

I committed this patch and then amended the commit message with some of
the info from your email.

> This patch only add the new windows to the codebase. My 
> follow-up e-mail (Retuning compression levels) suggests one 
> possible retuning of the compression levels 6, 7 and 8 that make 
> use of these new functions.

I'll address that separately.

Erik de Castro Lopo

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