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1392054 Electrophonic musical instruments PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 29 June 1972 [2 July 1971] 30426/72 Heading G5J Apparatus for converting a tone of frequency f into a lower tone of frequency xf comprises cascaded divide-by-two frequency dividers each corresponding to the digits of x in binary notation, all dividers corresponding to adjacent similar digits being connected to a NAND or NOR circuit together with the output of the NAND or NOR connected to the next adjacent lower group of dividers corresponding to adjacent similar digits. The ratios of the converters may be chosen to give mean-tone, equal temperament, or just intonation, or any other desired, such as 31-note equal temperament. For 12-note equal temperament three versions of a converter are described (Fig. 5, not shown) giving different degrees of accuracy. Fig. 3 shows a typical converter, which reduces the frequency by a factor 0À934593, or 0À111011110100001 in binary notation, this being one of the two intervals in the mean-tone intonation. The converter comprises a chain of divide-by-two dividers d 1 -d 18 . Each divider feeds the next and also, where required, feeds one of a set of NAND or NOR gates G 1 -G 7 . The dividers are notionally arranged in one-to-one correspondence with the bits of the conversion ratio, as shown. Each group of one or more dividers corresponding to identical successive bits feeds one gate (e.g. in the example shown dividers d 5 -d 8 feed gate G 4 ). Where the binary fraction ends in ... 01 the output of the divider corresponding to the last unit is fed to the same gate as the output of the previous divider, as shown. The later dividers d 8 -d 18 provide audio tones, and subsonic frequencies for tremolo circuits or the like. Two integrated circuit versions of a converter are described (Figs. 7 and 8, not shown). In an alternative type of converter (Fig. 6, not shown) the outputs of each group of divider are fed to an auxiliary gate. The output of this gate is inverted and fed to the main set of gates.
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