SE316808B - - Google Patents

Abstract

1,078,829. Vocoders. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 29, 1965 [April 6, 1964], No. 13170/65. Heading H4R. In a vocoder system each spectrum channel is sampled once per cycle of the fundamental frequency of the speech signal and the resulting signals transmitted in digital form. Fig. 1 shows a preferred embodiment in which speech from a microphone M is divided into a number of frequency bands by band-pass filters BP the signals from which are rectified by rectifiers G and passed through low-pass filters TP 1 to form analogue signals corresponding to the variations in energy of the individual frequency bands of the original speech. The speech is also fed through a low-pass filter TP 2 to a zero crossing detector ND to develop a pulse at the fundamental frequency of the speech. The fundamental frequency pulse is fed through a delay unit VZ, comprising e.g. cascaded monostable switching circuits, to synchronize the signal with the spectrum signals, before the signal is applied to a data processing unit EDV. The data processing unit controls the sampling switch S so that each spectrum channel is sampled one per pitch pulse. The resulting samples are fed via an analogue digital converter to the data processing system EDV for storage and subsequent transmission. The fundamental frequency signal is also digitized in the data processing unit by a counter.