GB1433351A - Method and apparatus for speech transfer over a norrow trans mission bandwidth by means of delta modulattion - Google Patents

Abstract

1433351 Bandwidth compression LICENTIA PATENT - VERWALTUNGS GmbH 13 April 1973 [14 April 1972] 17933/73 Heading H4R In speech bandwidth compression in which spaced sections of the speed signal are selected for transmission, voiced sections are of a length equal to a whole pitch period or to a portion extending between the zero crossing before the energy rich start of a pitch period and a zero crossing before the next pitch period, and unvoiced sections are of a length equal to a mean of the voiced pitch period, the sections being transmitted as delta modulations and being stretched to fill the gaps between sections. The modulated speech 1 is read alternately into stores 3, 4 associated with counters 31, 41 recording which store stages are occupied, at a rate determined by zero crossing detector 21 and read-out at a slower rate for multiplexed transmission 8. A pitch extractor 2 produces a pitch pulse at the start of each word and these pulses are monitored to produce a voicedunvoiced decision for encoded transmission. Characters identifying the start of words and representing the basic pitch frequency are also encoded for transmission, the latter occupying every 40th time slot for synchronization and level control at the receiver. Word storing is only effected when a zero crossing pulse is followed by a pitch pulse, otherwise the stores are reset, and the amount of voiced speech stored (typically 2/3) is controlled by the duration of the pitch period. The various characters are assembled at 7 in the required order for transmission. A signal representing the near pitch period may also be transmitted during unvoiced speech. At the receiver (Fig. 2, not shown) the data is demultiplexed at (18) and read-in to stores (13,14) when a new word character (e.g. 1100 ... 1100) is confirmed. The word is repetitively read-out to fill-in the gaps arising from expansion at the transmitter. The fundamental or mean pitch frequency or a frequency containing random pulses is generated at (12) corresponding to voiced or unvoiced speech. The read-out rate may be controlled according to pitch period signals received to automatically prevent overlaps or gaps in the read-out.