[flac-dev] [PATCH] Improve LPC order guess

[Martijn van Beurden]

Op 04-12-14 om 09:08 schreef Miroslav Lichvar:
> Just curious, is there any explanation why this improves the 
> compression ratio? Is it a bug? 

The error scale is used directly in the calculation of the 
expected bits per residual sample. Substituting the current code 
gives

bps = 0.5 * log(0.5 * M_LN2 * M_LN2 / 
(FLAC__double)total_samples * lpc_error) / M_LN2

which is equivalent to

bps =  0.5 * log(0.5 / (FLAC__double)total_samples * lpc_error) 
/ M_LN2 - 0.23

So, practically, this change increases the expected bits per 
sample by 0.23. Apparently this better estimates the residual 
bits per sample.

I've been experimenting with different values, and it seems 
increasing the bps even further is beneficial for some kinds of 
music, but not for others. This value seems to benefit all kinds 
of sources.