Patent ID: 8996365
Filing Date: 2015-03-31
Classification: G10L,H04R

Abstract:
1. A howling canceller mounted in an apparatus including a digital-to-analog converter that converts a digital received speech signal into an analog received speech signal, a power amplifier that amplifies the analog received speech signal output from the digital-to-analog converter, a speaker that plays back the analog received speech signal amplified by the power amplifier and outputs sound, a microphone that converts sound including playback sound output from the speaker into an analog transmitted speech signal, a microphone amplifier that amplifies the analog transmitted speech signal output from the microphone, and an analog-to-digital converter that converts the analog transmitted speech signal amplified by the microphone amplifier into a digital transmitted speech signal, the howling canceller comprising: an adaptive filter that operates the digital received speech signal with a tap coefficient to generate a pseudo echo, and updates the tap coefficient such that a residual signal is an optimal value; a subtractor that subtracts the pseudo echo from the digital transmitted speech signal to generate the residual signal; a delay circuit that connects to the subtractor and delays the residual signal output from the subtractor by a predetermined time; a threshold value setting circuit that directly connects to the delay circuit and sets a threshold value based on a peak value of the delayed residual signal output from the delay circuit, and an amplitude limiting circuit includes circuitry that directly connects to the delay circuit and limits an absolute value of an amplitude of the delayed residual signal output from the delay circuit to be equal to or smaller than the threshold value set by the threshold value setting circuit, and outputs the amplitude-limited residual signal to the digital-to-analog converter and the adaptive filter as the digital speech signal, wherein the threshold value is a minimum value of a first threshold value set in a linear region of the digital-to-analog converter, a second threshold value set in a linear region of the power amplifier, a third threshold value set in a linear region of the speaker, a fourth threshold value set in a linear region of the microphone, a fifth threshold value set in a linear region of the microphone amplifier, and a sixth threshold value set in a linear region of the analog-to-digital converter to prevent howling.