[flac-dev] Fix and question apodization functions

Martijn van Beurden mvanb1 at gmail.com
Fri Aug 1 10:51:00 PDT 2014


I was doing some speed and compression comparisons with various 
apodization/windowing functions, and found out that the 
definitions for the bartlett and bartlett_hann window in the 
FLAC codebase have been wrong since their introduction. The 
attached patch fixes that.

Furthermore, I found some peculiar behaviour of the gauss 
apodization that seems to expose bug. Using different windows 
does usually not change the encoding speed (only the number of 
them), but when I use -A gauss(0,05) (or gauss(0.05), it's 
locale-specific), the encoding time doubles. It seems to be when 
using STDDEV parameters between 0.1 and 0.01. This is also the 
case when using FLAC 1.3.0.

I used gprof to check and it seems that the time spend in the 
function FLAC__lpc_compute_autocorrelation_intrin_sse_lag_16 
increases 20-fold while the number of calls stays the same. 
Could this be a bug?
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