A vowel synthesizer

摘要

937,434. Secret transmission. NIPPON ELECTRIC CO. Ltd. Feb. 19, 1960 [Feb. 24, 1959], No. 5941/60. Class 40 (4). Vowel synthesis apparatus has a plurality of similar circuits equal in number to the number of formants in the vowels to be synthesized. Input terminals a 1 , a 2 , a 3 , Fig. 1, receive signals representing the centre frequencies F 1 , F 2 , F 3 of the first, second and third formants, respectively, while input terminals b 1 , b 2 , b 3 receive signals representing the amplitudes of the formants at their respective centre frequencies and an input terminal c receives a signal representing the pitch of the vowel. By " centre frequency " is meant the frequency which has the maximum energy in the formant spectrum. For synthesis of the first formant, a wave generator 1 is excited by the signal at the input a 1 to produce oscillations of frequency f 1 + F 1 where f 1 is a constant characteristic of the generator. These oscillations are modulated in a balanced modulator 2 with signals generated in a harmonic generator 3, such signals consisting of the pitch frequency and higher harmonics of the pitch frequency. An amplitude shaping filter 4 is interposed between the generator 3 and modulator 2. This may have low pass or band pass characteristics. The output from the modulator 2 is applied to an equalizer 5 having an attenuation characteristic, Fig. 3, to provide attenuated output waves having a wave envelope of similar shape to the wave envelope of the formant but extending over a different frequency range from that of the formant. The equalizer has minimum attenuation at frequency f 1 . Its output is applied to a demodulator 6 for demodulation by the signal of frequency f 1 + F 1 from generator 1. After passage through a filter 7 the signal, now a vowel formant, is applied to an amplifier 8, the gain of which is controlled by the signal from input terminal b. Amplifiers 81 and 811 receive the other vowel formants in a similar manner and the outputs of all three amplifiers are fed to a mixer 9. In a modification the output of wave generator 1 is f 1 -F 1 .