Patent GB-977271-A (GB)
Abstract: 977,271. Identifying spoken words. INTERNATIONAL BUSINESS MACHINES CORPORATION. March 1,1962 [March 20,1961], No. 7967/62. Heading G4R. In apparatus for identifying spoken words a signal representing the word is applied to a number of filters to obtain frequency component signals and to a further circuit to produce time dependent signals from the energy within a predetermined frequency channel,the frequency component signals and the time dependent signal are combined to identify the spoken word. The microphone 2 Fig. 3a, 3b is connected via a group of band-pass filters 102 to detectors 104. The detectors each derives the square of the input voltage so that the output represents the amount of power or energy in the associated channel e.g. P1. The microphone is also connected directly to a detector 104 in box 11 the output of which represents the total power Ptot in the speech signal. There may be seven filters selecting frequencies in bands 0-200 c.p.s. 200-400,400-800,800-1200,1200-1800,1800-2600 and 2600-4000. There are two further filters which pass respectively frequencies of 200-1400 and 1500-6000. These bands are shown in Figs. 2a and 2b as bands "8" and "9". There are also a vowel and a consonant filter in box 12 having frequency bands of 0-800 and 7000-8000 c.p.s. There, after smoothing in L-P filters 106, are applied to a timing circuit 20 together with the total power signal from detector 11. The time of a word is taken from the duration of the vowel portion and three signals are derived by integrating a signal which indicates that the vowel power is greater by a predetermined amount than the consonant power and that there is more than a certain total power present. This signal is integrated three times to generate three time signals t, t', t' all dependent on the time for which the vowel power exceeds a certain fraction of the total power of the speech signal. The three time signals are taken in line 13 to units 112 receiving also pairs of signals representing a function dependent on the natural logarithm of the ratio of powers in pairs of channels. These signals are derived by dividing the pair of power signals (such as P1 and Ptot) in units 108 to obtain the ratio P1/Ptot multiplied by a constant C (= 1000). The ratio signals are applied to logarithm function generators 110 and the log of the input (plus one to ensure a positive result) is applied to a circuit 112 shown in Fig. 12. The input function is here indicated as f(t), a function of time. A first signal is derived by integrating at 242 and at 248 dividing by the time signal t. At the end of the vowel interval the time signal has the value t 2  and the value at this instant is available on lead 250 for subsequent circuitry. The signal f(t) is multiplied by the t signal at 252, integrated at 254 and at 256 divided by t<SP>2</SP>, the second signal from the timing circuit 20. The second signal is available on lead 258 at instant t z . The input is also multiplied by t<SP>2</SP> at 260, integrated at 262 and divided by t<SP>3</SP> at 264 to produce the third signal on lead 266. Each circuit 112 has therefore three outputs defining in a modified form the three coefficients A, B, C, of the parabola shown in Fig. 2c as "second order approximation" i.e. a function of the form A + Bx + Cx<SP>2</SP>. This is the nearest approximation that can be obtained with a second-order function (a parabola) to the waveform representing the fluctuations in value of the logarithm of 1000 X the ratio P 8 /P 9  plus 1. The three coefficient signals from each circuit 112 are weighted by suitable resistors and applied positively or negatively to 45 discriminators each designed to discriminate between one of the pairs of possible words i.e. "0" and "1", "0" and "2" &c. The outputs of the descriminators are decoded in a diode matrix to give an output on a lead identifying the word spoken. If no output is produced on any lead a reject circuit operates. The apparatus may also be applied to the analysis of heart beats and other signals.