Energy band discriminator for echo canceller - producing binary output representative of frequency distribution of input signal samples

摘要

The discriminator is intended to inhibit operation of an echo estimate generator when the far-end signal includes significant energy over only part of the band. The input (X) is applied via an amplifier/separator (201) to a precision full-wave rectifier (202), which may be followed by a mu-to-linear-law convertor for sampled digital signals. The rectified version (MAG) is divided between two filters (203,204) with different time constants determining respectively its average and modified absolute values. These are applied to a comparison circuit (205) which generates a binary control signal for a switching gate in the echo canceller circuit. If the input signal contains energy over the whole band (from about 300 to 4000 Hz for telephone speech), the control signal is at a high logic level.