A Twelve-Channel Digital Echo Canceler

We describe a recently constructed 12-channel digital echo canceler that interfaces directly with the 8-bit μ255 PCM now standard for digital transmission in the telephone plant. The four most interesting features of the canceler are time sharing of circuitry to reduce per channel costs, floating-point multiplication, loop-gain normalization, and the use of a test channel for fault detection. Extensive laboratory and field testing has shown the canceler to be working well.