Audio processing in police investigations

David Luknowsky, Jeff Boyczuk


The various methods applied by the Audio and Video Analysis Section of the Royal Canadian Mounted Police (RCMP) to reduce the interferences and improve the intelligibility of audio recordings are discussed. Hum, a kind of tone which comes from powerlines and fluorescent lights can be removed with a comb filter. A series of individual tones at unequally spaced frequencies or tones whose frequency varies can be solved with the help of an adaptive filter. If tones are strong yet stationary and unevenly spaced, it can be removed with an inverse filter. A spectralinverse filter with shaping provides an amplitude boost to high voice frequencies and shape the spectrum to an averaged voice spectrum.


Adaptive filtering; Algorithms; Electric filters; Gain control; Information analysis; Radio interference; Signal processing; Spurious signal noise; Analogue noise; Audio processing; Filter parameters; Frequency noise

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