SE307977B - - Google Patents

Abstract

1,059,015. Vocoders. INTERNATIONAL BUSINESS MACHINES CORPORATION. May 21, 1965 [May 26, 1964], No. 21754/65. Heading H4R. A vocoder analyser periodically produces a set of digital signals representative of characteristics, e.g. the aggregate function, of the input signal which are inserted into a store, each set of signals produced is compared with the previous set stored in the storage device and only transmitted if there is more than a predetermined difference between the two sets of signals. In the Figure a speech signal is applied over lead 1 to the spectrum analysing filters 21-2n, rectifiers 31-3n and low-pass filters 41-4n. The outputs of the low pass filters are sampled periodically by gates 51-5n, operated over lines 61-6n from the analyser control apparatus, and the samples fed via analogue to digital converters 71-7n into a storage register 8 as a set of digital signals defining the aggregate function of the speech signal. After each sample has been taken, comparison circuit 10 is actuated by a signal on line 12 to compare the digital signals in register 8 with a previous set of digital signals stored in register 9. If the signals differ by more than a predetermined amount, e.g. differences of more than two units in the numbers stored in respect of more than two channels, then a signal is transmitted via a decision circuit 11 to initiate the transfer either in serial or parallel form of the contents of register 8 to the output line 13 and also to replace the contents of register 9 by the contents of register 8 ready for further comparisons. If there is no substantial difference revealed by the comparison then the contents of register 8 are discarded, register 9 is undisturbed and a signal is transmitted via circuit 11 to indicate at the receiver that the previously transmitted aggregate function signal is to be re-used.