You should use this version instead; it's better.
Note that this uses a bilinear transform and so is not accurate at high frequencies.
Apply an A-weighting filter to a sound stored as a NumPy array.
Use Audiolab or other module to import .wav or .flac files, for example. http://www.ar.media.kyoto-u.ac.jp/members/david/softwares/audiolab/
Translated from MATLAB script (BSD license) at: http://www.mathworks.com/matlabcentral/fileexchange/69
hum.. i think i understand.. to be honest i'm not so comfortable with digital filtering.
i have implemented this filter in embedded software and i will made some tests in next weeks in real situation comparing my implementation and sonometer.
but my preliminary tests on bench shows nothing bad. (i'm using 20k sample rate)