1. Field
The embodiments discussed herein are directed to processing of sound signals.
2. Description of the Related Art
A microphone array includes an array of plural microphones and may give directivity to a sound signal by processing the sound signal obtained by receiving and converting sound. (see to the extract of references about a microphone array: Journal of the Acoustical Society of Japan Vol. 51 No. 5, “A small special feature—microphone array—”, pp. 384-414 (1995))
In a microphone array system, sound signals derived from plural microphones may be may be processed such that undesired noises in sound waves coming from directions different from the direction in which desired signal is received or coming from the direction of suppression may be suppressed, in order to improve the SNR (signal-to-noise ratio).
Typically a noise component-suppressing system as disclosed in Japanese Laid-open Patent Publication No. 2001-100800, includes a first means for detecting sound at plural positions to obtain an input signal at each different sound receiving position, frequency-analyzing the input signal, and obtaining frequency components for different channels, a first beam former processing means for suppressing noises coming from the direction of a speaker and obtaining desired sound components by a filtering process using filtering coefficients that provide lower sensitivities to frequency components of the various channels outside the desired direction, a second beam former processing means for suppressing speech of the speaker and obtaining noise components by a filtering process that provide lower sensitivities to frequency components of the channels obtained by the first means outside the desired direction, an estimation means for estimating the direction of noise from filter coefficients of the first beam former processing means and estimating the direction of intended speech from the filter coefficients of the second beam former processing means, a modification means for modifying the direction of arrival of the intended speech to be entered into the first beam former processing means according to the direction of intended speech estimated by the estimation means and modifying the direction of arrival of noise to be entered into the second beam former processing means according to the direction of noise estimated by the estimation means, a subtraction means for performing a spectral subtraction operation based on the outputs from the first and second beam former processing means, a means for obtaining a directivity index corresponding to the time differences between arriving sounds and amplitude differences from the output from the first means, and a control means for controlling the spectral subtraction operation based on the directivity index and on the direction of the intended speech obtained by the first means.
Typically, a directional sound collector as disclosed in Japanese Laid-open Patent Publication No. 2007-318528, includes sound inputs from sound sources existing in plural directions are accepted and converted into signals on the frequency axis. A suppression function for suppressing the converted signal on the frequency axis is calculated. The calculated suppression function is multiplied by the amplitude component of the original signal on the frequency axis, thus correcting the converted signal on the frequency axis. Phase components of converted signals on each frequency axis are calculated at each individual frequency. In this way, the differences between the phase components are calculated. A probability value indicating the probability at which a sound source is present in a given direction is calculated based on the calculated differences. Based on the calculated probability value, a suppression function for suppressing sound inputs from sound sources other than sound sources lying in the given direction is calculated.