Abstract: Stereo sound signals are reproduced directly from loudspeakers (SP(L), SP(R)). By using a sum signal and a difference signal of the stereo sound signals as a reference signal, and according to a cross spectrum calculation of the reference signal with a microphone-collected sound signal, calculation is performed to obtain transfer functions of four sound transfer systems between the loudspeakers (SP(L), SP(R)) and microphones (MC(L), MC(R)). The transfer functions obtained are subjected to inverse Fourier transform to obtain impulse responses, which are set in filter means (40-1 to 40-4) to create echo cancel signals and perform echo canceling. This solves the problem of an indefinite coefficient in the echo cancel technique of a multi-channel sound signal.

Abstract: Two signals, which are mutually correlated, are subjected to a principal component analysis and converted into two signals being put in an orthogonal relation, thereby generating two signals being non-correlated. Those two signals are reproduced by speakers, and the voice generated from the speakers are collected by microphones. The cross spectra of a signal as the result of subtracting an echo canceling signal from a voice collected by each microphone, and a voice before it is generated from the speaker, are obtained. Those cross spectra are ensemble-averaged for a predetermined period of time, and inverse Fourier transformed, thereby producing impulse response estimation errors of each filter. Impulse responses of those filters are updated so as to cancel those impulse response estimation errors.

Abstract: Sound picked up by a microphone of a first sound field is reproduced by a speaker of a second sound field, and a sound picked up by a microphone of the second sound field is reproduced by the speaker of the first sound field. Sound pressure detection section detects a sound pressure of a sound present in the second (or first) sound field picked up by the microphone of the second (or first) sound field, other than a sound reproduced by the speaker of the first (or second) sound field. Other sound pressure detection section detects a sound pressure with which the sound picked up by the microphone of the second (or first) sound field and reproduced by the speaker of the first (or second) sound field is picked up by the microphone of the first (or second) sound field. Sound-pressure-difference detection section adjusts a gain of an automatic gain adjustment section in such a manner that the two detected sound pressures assume a predetermined relationship.

Abstract: An acoustic echo erasing apparatus which generates a pseudo-echo component from an audio reception signal (a vector x.sub.1) using an adaptive filter, and removes the pseudo-echo component from an audio transmission signal (a vector y). The apparatus extracts a feedback component depending only on the audio reception signal from the audio transmission signal, and passes the audio reception signal through the adaptive filter to generate the pseudo-echo component while setting a transfer characteristic of the adaptive filter in accordance with the feedback component.

Abstract: A frequency analyzing method according to the invention is a method of analyzing frequency components of an original signal. The method has: a spectrum detecting step of detecting, from the original signal, energy levels of components of a predetermined number of orthogonal function waves which have waveforms each having same start position and end position in a predetermined time window and in which the number of occurrences of periods in the predetermined time window or frequencies are different from each other; and an orthogonal function wave changing step of changing at least one of the start position and the end position within the predetermined time window after completion of the spectrum detecting step, wherein the spectrum detecting step and the orthogonal function wave changing step are alternately repeated.