[pulseaudio-discuss] Updates to filtering work. Review requested.

[Justin Chudgar]

https://github.com/justinzane/pulseaudio

Gentlemen, Ladies and Bots: 

Thanks again for all your help getting me to this point. Based on various 
input, I have done a major refactor of what was module-lfe-lp. The actual 
filtering code now lives in pulsecore/biquad-filter.c/h so that it may be used 
by other modules or by pulse itself. Module-lfe-lp has been renamed module-
lfe-lowpass-sink.c and now relies on biquad-filter to do the heavy lifting. 

I have tried to cleanup most of the fprint and comment cruft and have moved 
all doc comments to biquad-filter.h. You will note that I wrote the biquad code 
with the assumption that it will get extended to handle other filter types, 
like notch and bandpass, as well as 2nd, 4th, 6th and 8th order filtering. This 
is not used by my module, but it seemed logical to enable easy extension of 
functionality as needed.

I would appreciate your continued review and guidance. For your convenience, I 
attached a graph of the power spectral density comparison for a standard 
surround-51 setup with lpfreq=200.0Hz. To my uneducated eye, it looks like 
things are working.

Justin
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