Patent ID: 8213636

Claim:
A method of reconstituting low frequencies of an audio signal output by a sound playback device ( 11 , 12 ) having a low cutoff frequency (F 0 ), the method comprising the steps of: filtering the audio signal by means of a lowpass filter ( 101 ) with a cutoff frequency substantially equal to said cutoff frequency (F 0 ) of the sound playback device; determining a fundamental frequency to be reconstituted from the lowpass filtered audio signal; and generating a harmonic signal (S harm ) associated with said fundamental frequency to be reconstituted; the method being characterized by the steps of: detecting a time envelope (env(t)) of the lowpass filtered audio signal; adapting the dynamic range of said time envelope (env(t)) as a function of the frequency band under consideration, wherein adapting is performed by compression/expansion ( 122 a ) of the time envelope (env(t)), further wherein a feedback loop ( 122 b ) conditionally controls the compression/expansion after comparing the level of the compressed/expanded signal with a predetermined threshold (S); and reinjecting said harmonic signal in phase into said audio signal by addition, after multiplying said harmonic signal (S harm ) with the adapted time envelope (env adapt (t)).