DEVICE FOR EXCITATION CONTROLLED SMOOTHING OF THE SPECTRUM-CHANNEL SIGNALS OF A VOCODER

摘要

1,073,203. Vocoders. INTERNATIONAL BUSINESS MACHINES CORPORATION. Match 15,1966 [March 25, 1965], No. 11188/66. Heading H4R. Channel. vocoder in which each spectrum analysis channel includes a band-pass filter, a rectifier, and a low-pass filter, or integrator circuit; has a voiced-unvoiced detector the output from which is used to lower the cut-off frequency of the low-pass filter, or increase the integration time of the integrator circuit, when unvoiced sounds are detected; in order to reduce noise in the channels. The voiced-unvoiced detector may cause switching between two alternative filters provided for each channel, Fig. 2 (not shown), or it may modify the filtercircuit, e.g. by operation of switch Si. in the filter of Fig. 3. A typical integrator circuit which might be used in each spectrum analysis channel is shown in Fig. 5 in which the spectrum channel signal is applied to band causes capacitor C to be discharged by an amount proportional to the current applied through R 1' Periodically a signal is applied to line a to cause TR 2 to conduct to charge C up to the supply potential. The charging current, which will depend on the total discharge of C since the last charging pulse, flowing through R3 will produce an output pulse on Ki1 the amplitude of which is proportional to the integral of the spectrum channel signal over a time equal to the period of the pulse signal applied to line a. The voiced-unvoiced discriminator output is employed to increase the period between the pulses applied to line b during unvoiced sounds.