The sinusoidal transform coder (STC): A high-performance multi-rate speech coder

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The sinusoidal transform coder (STC): A high-performance multi-rate speech coder

McAnlay, R.J. / Quatieri, T.F.

An analysis/synthesis system based on the sinusoidal speech model has been developed that produces synthetic speech that is perceptually equivalent to the original: A zero-phase harmonic version of this system, using only pitch, voicing and amplitude information, has achieved a Diagnostic Aceptibility Measure (DAM) of 63.0. This shows that high-quality synthetic speech can be achieved at low rates provided the sine-wave amplitude information is coded efficiently. One approach has been to linearly interpolate the sine-wave amplitudes and then frequency-warp, downsample and code using DPCM quantization. Another has been to fit an all-pole model to the sine-wave amplitudes and code the resulting reflection coefficients. In either case, frequency domain post-filtering is needed to reduce the effects of coder noise. The system, called the Sinusoidal Transform Coder (STC), has been implemented in basic 4800 b/s form using two ADSP 2100 fixed-point DSP chips, with more complex versions at 2400 b/s and 4800 b/s requiring an additional DSP chip. The STC system is designed for, and being evaluated in, application environments requiring robust performance, including military airborne and civilian air traffic control communications systems.