Abstract
Practically all echo suppressors presently used in long-distance telephone circuits operate on the principle of cutting off the sending circuit when the receiving speech level is greater than the sending speech level, thereby suppressing echoes. Therefore, they generate a faulty speech problem due to the cutting off of speech in simultaneous talking, thus making speech unnatural. To correct this fault, a blockless echo suppressor which, unlike the usual echo suppressors, generates a signal equivalent to the echo to be canceled, has been developed. In the suppressor, a signa1 equivalent to an echo is produced from the convolution of a received speech signal and an echo-path impulse response which is stored in a memory in advance of the commencement of commercial service. It has been confirmed by subjective evaluation that an echo suppressor of this kind manufactured for trials has better talking quality than any other kind of typical echo suppressors now in service. This is because an echo is effectively suppressed more than 30 dB below the transmitted speech signal, and speech is not cut off in this suppressor.
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