Pulse-Code Modulation to Voice Conversion--Binary Rate Multiplier Differential Pulse-Code-Modulation Decoder

An experimental and computer investigation of a 9-bit, 16-MHz binary rate multiplier (BRM) used in converting digital signals differential pulse-code modulation (DPCM) to analog signals (voice) is reported in this paper. The physical electronic circuitry was provided with a stream of real-time digital samples at a 32-kHz rate from a magnetic tape which had been generated by a computer simulation. The output power spectrum of the electronic circuit was observed and compared to that of the computer calculation. Before exciting the experimental circuit with the digital samples the circuit noise in absence of signal was measured at - 11 decibels above a reference noise using a C message weighting filter (dBrnC0). Three different input signals were used to probe the BRM. Two consisted of single sine waves at various levels and in one test ten arbitrary phase superimposed sine waves were used to simulate white noise. Experimental and theoretical results are in good agreement and together demonstrate that the BRM approach is a viable technique for digital-to-analog (D/A) conversion.