Patent GB-1179029-A (GB)
Title: Apparatus for Recognising a Speech Signal
IPC: H03K5/22
Filed: 1967-04-19
Abstract: 1,179,029. Speech recognition. INTERNATIONAL BUSINESS MACHINES CORP. 19 April, 1967 [2 May, 1966], No. 17934/67. Heading G4R. Speech . recognition, apparatus determines characteristics of successive pulse periods of a speech signal, accumulates the levels of correspondence between these characteristics and stored characteristics compared with them, and indicates when the accumulation exceeds a predetermined value after the comparison of a predetermined number of characteristics. The identity of a person is verified by comparing characteristics of a particular spoken word (or words) with stored characteristics of the word as spoken by the true person. The characteristics used are the voltage and time of occurrence of the first 3 peaks and 2 troughs of each of a series of pulse periods of the speech, a pulse period being a period of the voiced component of the speech. The voltage characteristics are all positive by choice of the zero of voltage. The characteristics mentioned for representative pulse periods of the word as spoken by the true person are retrieved from a back-up store .and placed in a closed-loop shift register. After detection of the beginning of .a pulse period in the input speech (i.e. that from the person, whose identity is to be verified), detection of the first peak causes the stored voltage and time characteristics for the first peak in each of three adjacent pulse period sections of the shift register to be subtracted from the actual voltage value of the input first peak (converted to digital form) and the time (specified by a clock-driven time counter) respectively, the six subtractions being accomplished by adders since the characteristics are stored in the shift register in negative form. The differences are squared and added into respective ones of three accumulators (via preliminary adders), one accumulator corresponding to each of the three shift register sections used. The next two troughs and two peaks are treated similarly, the shift register being shifted to bring the stored characteristics for these troughs and peaks into position for use, and the squared differences being added into the same accumulators. After the total of five troughs and peaks, a second counter causes the contents of the accumulator holding the smallest value, representing the difference between the input pulse period and the most similar of the three stored pulse periods used, to be gated to a sum accumulator, and also causes the shift register to be so shifted that the centre one of the three stored pulse periods which will be compared with the next input pulse period will be the most similar stored pulse period just determined. The above operations are repeated for each of the following input pulse periods, the sum accumulator accumulating a measure of the total deviation so far between the input and stored characteristics. The time counter, second counter and the accumulators (except the sum accumulator) are reset for each pulse period. After each pulse period, the second counter also gates the contents of the sum accumulator to a divider to be divided by the number of pulse periods which have so far occurred, as specified by a third counter. The quotient is compared with a threshold and if it exceeds it, a "stop non-verify" signal is produced which indicates the identity is false and stops operations. The totality of characteristics in the shift register is followed by a special mark and when all the stored characteristics have been used this is detected in a particular stage of the register and produces an "identity verified" signal if the "stop non- verify" signal is absent. The stored characteristics could be in analogue form and analogue circuitry be used. The input speech could be compared with a plurality of stored sets of characteristics, each set as above, to identify the speaker.