Companded Predictive Delta Modulation: A Low-Cost Conversion Technique for Digital Recording
Adigital recording system is described that employs a type of analog-to-digital converter other than the 16-bit linear pulse-code modulation converters commonly in use. The conversion process, called companded predictive delta modulation, differs from adaptive delta modulation in that the input signal is dynamically (in both amplitude and spectrum) adjusted by a voltage-controlled amplifier and then passed through a fixed (nonadaptive) delta modulator. Dither is added to provide a white noise floor and minimize low-level distortion. Instead of a single integrator, the delta modulator uses a second-order feedback filter, which increases its dynamic range substantially. Since delta modulators have low sensitivity to bit errors, the error-correction circuitry is relatively simplified. A convolutional error-correction code was chosen in this application.
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