1.  Field of the Invention
The present invention relates to an echo suppressor, and more particularly to an echo suppressor for use in, for example, a telephonic conference system, such as a video teleconference system. 
2.  Description of the Background Art
For example, in a loudspeaker-assisted telephone conference system such as a video conference system or telephone conference system, when the talker speaks on a microphone, for example, part of his or her voice radiated from loudspeakers may be caught by microphones to return to the talker side in the form of acoustic echo signals.  Since acoustic echo signals may severely hinder telephone speech quality, a lot of research and development has been heretofore conducted solutions for suppressing acoustic echo. 
Solutions for suppressing acoustic echo may include echo suppressors.  The echo suppressor may be implemented by a sort of calculator calculating echo path characteristics, estimated echo signals and an echo suppression gain from far-end and near-end input signals, and multiplying the near-end input signal by the echo suppression gain to thereby suppress acoustic echo signals.  One of such echo suppressors is proposed by C. Faller, et al., “ ESTIMATING THE DELAY AND COLORATION EFFECT OF THE ACOUSTIC ECHO PATH FOR LOW COMPLEXITY ECHO SUPPRESSION”, Proc.  Intl.  Works, on Acoust.  Echo and Noise Control (IWAENC) 2005, pp.  53-56, October 2005. 
According to C. Faller, et al.,  the proposed echo suppressor calculates an echo path characteristic based on far-end and near-end input signals of past frames.  The resultant echo path characteristic is multiplied by the far-end signal to obtain an estimated echo signal.  The echo suppressor in turn calculates an echo suppression gain based on the near-end input signal and estimated echo signals.  The near-end input signal is multiplied by the echo suppression gain, thus suppressing echo signals. 
However, incoming far-end signals may generally include frequency bins corresponding to the valleys of the fine structures of speech signals and/or having frequency components smaller on the spectrum envelope of sound signals.  Therefore, the frequency components of small frequency bins in a far-end signal may be buried in frequency components of the corresponding frequency bins of background noise. 
Under those circumstances, when the echo suppressor set forth in C. Faller, et al.,  calculates out echo path characteristics of the frequency bins, values entirely different from actual echo path characteristics are obtained to update the echo path characteristics accordingly.  Consequently, estimated echo path characteristics may become different from actual ones.  This raises a problem that acoustic echo signals cannot be suppressed appropriately.