ABSTRACT
Waveform coders, as their name implies, attempt to copy the actual shape of the waveform produced by the microphone and its associated analogue circuits. The amplitudes of the samples are then represented as a digital code with enough digits to specify the signal ordinates sufficiently accurately. The amplitude of the quantizing noise of simple pulse code modulation is determined by the step size associated with a unit increment of the binary code. The time resolution properties of the auditory system ensure that masking of quantizing noise by the higher-level wanted signals is effective for at least a few milliseconds at a time, but instantaneous companding will give finer quantization near zero crossings even for large-amplitude signals. A deltamodulator uses its transmitted digital codes to generate a local copy of the input waveform. There are properties of speech communication that can be heavily exploited in speech coding.
