This paper describes a real-time computer implementaation of a fourth-order adaptive predictive coder (APC) which transmits speech at 6400 bits/s. To reduce the demands on the central processor, the terminal uses the average magnitude difference function (AMDF) for pitch extraction and calculates the predictor coefficients and reflection coefficients assuming stationarity of the input data. With 16-bit fixed-point arithmetic processing, the coder achieves an intelligibility score of 87 percent on the diagnostic rhyme tests (DRT) and produces speech with acceptable voice naturalness even in the presence of acoustic background noise.