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Re: Octave band filter


Octave filters have characteristics that make sense in geometric terms. In other words, just as in 'arithmetic' filters the centre frequency (CF) is the arithmetic mean of the upper and lower cutoffs (CL and CU), in other words (CU-CL)/2, in octave filters the CF is the geometric mean of the CL and CU, in other words CF = sqrt(CU*CL).
The bandwidth measured in octaves is: BW = log10(CU/CL)/log10(2).
Another aspect of octave filters is Q. Q refers to the sharpness of the filter and is: CF/(CU - CL).
So: an octave filter with CF of 1000 Hz and BW of 200 Hz has a CU of 1414 Hz and CL of 707 Hz. The Q is 1.41
For more on Q check: http://www.prosoundweb.com/studyhall/studyjump.php?pdf=bandwidthchart for a pdf chart.

Hope this helps

A. Sarampalis
Research Associate
House Ear Institute,
Department of Auditory Implants,
Los Angeles