Patent ID: 8218788

Claim:
An anti-feedback device comprising: an anti-feedback filter provided in a closed loop including a microphone and a speaker that are disposed in a single acoustic space, wherein an adaptive target signal transfer system includes at least a route from the speaker to the microphone and the anti-feedback filter; a first input processing section that selects a signal belonging to a specific band from a signal output from the adaptive target signal transfer system, and that down-samples the selected signal to a sampling frequency suitable for the specific band and outputs the down-sampled signal; a second input processing section that selects a signal belonging to the specific band from a signal input to the adaptive target signal transfer system, and that down-samples the selected signal to a sampling frequency suitable for the specific band and outputs the down-sampled signal; an adaptive filter that subjects a signal output from the second input processing section to filtering processing, to thus generate a simulated output signal that simulates a signal output from the adaptive target signal transfer system by way of the first input processing section, that cancels out the simulated output signal by means of the signal output from the first input processing section and outputs a signal subjected to cancellation, and that updates a filtering coefficient for the filtering processing so that the simulated output signal simulates the signal output by way of the first input processing section based on the signal subjected to cancellation; an output processing section that up-samples the signal output from the adaptive filter to the same sampling frequency as that at which the signal output from the adaptive target signal transfer system is sampled and that adds the up-sampled signal to a signal outside the specific band in the signal output from the adaptive target signal transfer system and outputs a result of addition to the closed loop; a time-frequency conversion section that determines an amplitude characteristic of the closed loop in accordance with the filtering coefficient used for the filtering processing of the adaptive filter; and a filter control section that controls a filtering characteristic of the anti-feedback filter so that a peak gain of a frequency among gain of the specific band in the amplitude characteristic of the closed loop determined by the time-frequency conversion section is suppressed, that estimates a gain of the closed loop outside the specific band in accordance with the amplitude characteristic in the specific band of the closed loop determined by the time-frequency conversion section, and that controls an amount of suppression of the anti-feedback filter outside the specific band in accordance with a result of estimation.