Patent GB-1320970-A (GB)
Title: Method and apparatus for generating speech
IPC: G06F3/16
Filed: 1970-12-23
Abstract: 1320970 Speech synthesizers COGNITRONICS CORP 23 Dec 1970 [23 Dec 1969] 61088/70 Heading H4R In a speech synthesizer a number of characteristic sound cycles of voice sounds are stored, selected sequentially, and each reproduced a number of times to synthesize speech. As described with respect to Figs. 2A and 2B the store 10 comprises a magnetic drum on which information is recorded digitally. Two tracks on the drum are used for timing the operation of a control signal generator and providing basic timing for the synthesizer. Four tracks store program information in respect of each word which the synthesizer is to reproduce. Each word which is to be reproduced by the synthesizer is broken down into a number of elemental sounds each comprising a pitch period cycle which is reproduced a predetermined number of times to synthesize the elemental sound. The pitch period cycles are stored in sectors of 40 sound tracks 14 on the drum 10, each sector comprising 256 bits to define the cycle waveform, and there being 8 sectors on each track. The elemental sounds are reproduced from the sound tracks under the control of the program tracks 12, of which there are four, each track having 128 sectors, each defining an elemental sound, each sector being 16 bits long. Each program sector includes 3 bits defining the sector and 5 bits defining the track of the pitch period cycle to be reproduced for the elemental sound together with 2 bits specifying the number of times the sound is to be reproduced, three bits to define the gap to be left between each pair of repetitions of the cycle, to govern the pitch of the reproduced sound, and a further 2 bits to control the envelope of the reproduced waveform. In operation a computer in response to an optical reader, voiced sound input, or punched cards etc., produces from a store information as to the phonetic equivalents of the words to be synthesized, and program instructions as to their characteristic sound cycle content, in the form of program locations expressed as 7 bits defining the position on a program track defined in a further two bits. The 9 bit program location is fed into a store 68, 70 where the last two bits effect the selection of the appropriate track while the first 7 bits are compared with a program sector counter, controlled by the timing tracks on the drum, to cause read out of the appropriate program sector of 16 bits into the store 42. At the appropriate time, under the control of the control signal generator 40, the information in respect of the particular sound cycle to be reproduced next is fed from the store 42 into the store 78 to be compared with the state of a sound sector counter 86, controlled by the drum timing tracks 20, 22; to effect the transfer of the appropriate sound cycle sector from the sound tracks 40 into a recirculating memory track 16 on the drum, to provide a fast access store. Simultaneously the number of repeats of the pitch cycle is fed from store 42 to the cycle repetition counter 138 the pitch information is fed to pitch store 150 and envelope information to a buffer 172. The read head of memory track 16 is spaced # of a drum revolution from the write head and during synthesis the read head output is fed back to the write head so that the sound cycle information is available every #th drum revolution. For reading out on synthesis the speech cycle in memory 16 is fed into the memory 18 and the shift register 112. The first 32 bits of the cycle are entered into the shift register and the remaining 224 bits into the recirculating memory 18, having read and write heads spaced by the 224 bit interval. Four bit groups, from part 116  of the shift register, representing amplitude samples of the cycle, are fed to a converter 120 and low pass filter 124 to provide analogue output signals. Read out of 32 bits from the register 112 requires the time taken for recirculation of 224 bits in memory 18 so that the complete cycle can be read out continuously through register 112 after the read out of one complete sound cycle, cycle repetition counter 138 is decremented by one and the cycle repeated until counter 138 has been decremented to zero, when the cycle being reproduced will be replaced by the succeeding sound cycle called for by the program. After each successive repeat of a cycle a number of #th drum revolution gaps is left, to enable variation of the pitch of the reproduced sound. The number of #th drum revolutions is determined by the pitch signal stored in location 56 of the store 42 which is fed to the pitch store 150 and compared with the state of a counter 156 counting #th drum revolutions after the end of a sound cycle, and a repeat only being enabled after coincidence is established between the two counters. In addition for natural speech the amplitude of the last few sound cycles before the end of a word may be progressively reduced, this is provided by the AVC circuit 126 controlled by a ramp generator 168 whose operation is initiated through the control signal generator in accordance with the program set into location 58 of the program store 42.