Patent GB-547505-A (GB)
Title: Production of artificial speech
IPC: G10L19/02
Filed: 1941-03-07
Abstract: 547,505. Secret transmission. STANDARD TELEPHONES & CABLES, Ltd. March 7, 1941, No. 3109. Convention date, March 16, 1940. [Class 40 (iv)] [Also in Group XL] In a system in which speech is synthesized from locally generated currents in accordance with signals indicative of the momentary energy in a number of bands into which the original speech is arbitrarily divided, these signals, instead of selecting from a corresponding number of fixed filters arranged for insertion between the local sources and the loudspeaker, control the tuning of a pair of filters which correspond to the resonance chambers of filters into which the mouth cavity is divided by the tongue in speech. Specifications 540,116 and 543,239 are referred to. Circuit arrangements.-Speech currents to be analysed are kept at a constant level in apparatus 2. A portion passes via filter 7 to a circuit which in known manner, when a voiced sound is present, produces a direct current of which the value depends on the fundamental frequency of such sound and this in known manner controls the fundamental frequency of a relaxation oscillator 47 in the synthesizer. This current also biasses amplifiers 54, 95 which are fed from a noise source 55 so that the former is disabled and the latter is operative. A high frequency portion is selected by a filter 70 and passed to a rectifier 71 to produce the various difference frequencies and these control a differential relay 76 through low-pass filters 72, 74 with different ranges. When a pure voiced sound is present, the lefthand winding of the relay has a preponderating effect and a 70-cycle current is sent to line and operates a relay 50 in the synthesizer. The bias conditions of amplifiers 54, 95 and the condition of relay 50 determine whether the relaxation oscillator or the noise source or both together are to feed the variable filters over circuit 56 and contacts of 53 which is always energized when speech is present. Another portion of the speech current passes via a delay network and an equalizer 3 or 4, according as voiced sounds are present or not, to a number of filters 23-27 over which differential relays 30-44 are controlled. When any filter passes more current than either of its neighbours, a corresponding pair of relays is energized and a characteristic 105-cycle source is coupled to the line. In general, each vowel sound will cause the operation of two pairs of relays and the transmission of a 105-cycle signal of a characteristic strength. The sources may derive their current from a single generator. The signal, after rectification at 93, controls the saturation of the inductances of filters 57, 58 to give them characteristics corresponding to those of the chambers formed in the mouth by the tongue in making the sound concerned. Each inductance is built up from four coils of which two are of large inductance and are unaffected by the current through them and the other two are varied in opposite directions by the signal. By this means an arrangement having the desired law can be designed. When mixed sounds are to be reproduced, damping resistances 96, 97 are connected up. In response to the sudden fall in energy due to a stop-consonant, a voltage is built up across a large inductance 18 in the analyser and a 30-cycle signal is sent out to operate a magnet 52 controlling a potentiometer and so give a momentary reduction of the current fed to the filters. The results of the analysis may be recorded and the synthesizer controlled by the record. Owing to the fact that only low frequencies are involved such a record may be driven very slowly. For instance, a record of a size to play for 15 minutes, with normal recording, would play for five hours. Specifications 466,327 and 543,238 also are referred to.