Patent ID: 7899195

Claim:
An adaptive howling canceller for use in a sound-reinforcement system including a microphone installed in a given space for collecting therefrom an audio signal, a speaker installed in the space such that an acoustic feedback path is formed from the speaker to the microphone, and an amplifier connected between an output of the microphone and an input of the speaker for amplifying the audio signal fed from the microphone to provide an electric signal to the speaker, the adaptive howling canceller being used for suppressing a feedback component of the audio signal fed back from the speaker to the microphone through the acoustic feedback path with a given time delay, the adaptive howling canceller comprising: a delay section that adds a time delay corresponding to the time delay of the acoustic feedback path to the electric signal which is provided from the amplifier to thereby output the electric signal added with the time delay as an output signal; a first adaptive filter that has an input for receiving the output signal fed from the delay section and that filters the output signal of the delay section with a first filter coefficient, which is periodically updated at an update interval; a second adaptive filter that has an input for receiving the output signal fed from the delay section and that filters the output signal of the delay section with a second filter coefficient, which is periodically updated at another update interval set shorter than the update interval of the first filter coefficient; a first adder section that has an input for receiving an output signal fed from the first adaptive filter, and that subtracts the output signal of the first adaptive filter from the audio signal fed from the microphone to thereby provide an output signal as a result of subtracting; and a second adder section that has an input for receiving an output signal fed from the second adaptive filter, and that subtracts the output signal of the second adaptive filter from the output signal of the first adder section to thereby provide an output signal as a result of subtracting, wherein the output signal from the first adder section is inputted into the first adaptive filter, and the output signal from the second adder section is inputted into the second adaptive filter, wherein the output signal from the second adder section is inputted through the amplifier to the speaker and to the delay section as the electric signal, wherein the first filter coefficient is updated by the first adaptive filter so as to simulate a transfer function of the acoustic feedback path based on the output signals of the first adder section and the delay section, and the second filter coefficient is updated by the second adaptive filter so as to simulate the transfer function of the acoustic feedback path based on the output signals of the second adder section and the delay section, and wherein the second adaptive filter resets the second filter coefficient to an initial value when the first adaptive filter updates the first filter coefficient.