Abstract: In reconstructing the analog waveform from a syllabically companded delta modulated digital signal transmitted over a TDMA communication channel operating at near its maximum channel capacity, the noise created in a mid-talkspurt freeze-out is greatly reduced by interpolating the amplitude of the waveform during the freeze-out at the receiver as that of the waveform in the previous period. This makes the quality of voice transmissions in the face of freeze-outs substantially better than prior art techniques which induce background noise during freeze-outs, without the necessity of transmitting a voice activity compression (VAC) mask to control the operation of the interpolation apparatus in the receiver. The interpolation occurs for the first 15 msec sampling period following either a freeze-out or a true VAC operation.

Abstract: An adaptive delta modulation system is disclosed which features an improved digital compandor which may be used with a digital integrating network. The compandor executes a companding algorithm having a nonlinear characteristic to provide a rapid increase in step size to follow the fast rising start or fast decaying end of talkspurts in input signals so as to minimize any slope overload distortions and to provide a small increase or decrease in step size during the smooth portion of the talkspurts in input signals to reduce any granular noise effect. The step size generated by the compandor is directly related to the input signal level, providing a maximum companding range in which good signal-to-noise characteristics are preserved for the soft or low voiced speaker as well as for the loud voiced speaker and providing a fast transient response most suitable for telephone applications.