GB1264143A - - Google Patents

Abstract

1,264,143. Pulse generating and manipulating circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 12 Feb., 1969 [15 Feb., 1968], No. 7630/69. Heading H3T. [Also in Division G5] General.-In an electronic musical instrument, electric signals representing the different tones of a musical scale are obtained from a circuit chain comprising a master oscillator driving a series of frequency dividers by means which combine the outputs of selected members of the chain. In one form of the instrument, the dividers may be decade dividers having division factors in the sequence 10-1, 10<SP>-2</SP>, 10<SP>-3</SP> ... 10<SP>-6</SP>, a desired tone equal to, say, 1À059463 times the master oscillator frequency being obtained by adding to the master oscillator output occurring during a given time 0, 5, 9, 4, 6 and 3 times the outputs obtained respectively from the 10<SP>-1</SP>, 10<SP>-2</SP>, 10<SP>-3</SP> ... 10<SP>-6</SP> dividers. In an alternative arrangement, tones may be obtained by subtracting divider outputs from a higher frequency. In place of the decimal dividers, ternary dividers may be used. A preferred arrangement, however, employs binary dividers. Detailed arrangements.-The use of binary division is illustrated in Fig. 2 which is an arrangement for obtaining the tone of an equal-tempered, 12-note scale. O denotes the master oscillator and D 1 to D 11 denotes the chain of divide-by-two frequency dividers. The lowest frequency of the scale, normalized to binary number 1À000,000,000,0, is obtained from the output of the first divider D 1 , whilst the other tones of the scale are obtained from adding circuits of which only three A 1 , A 2 and A 10 are shown which combine the outputs from selected dividers. Thus, adding circuit A 1 produces a tone related to the lowest tone by the binary number 1À000,011,110,1 and obtained by adding the outputs from dividers D 1 , D 6 , D 7 , D 8 , D 9 and D 11 . This corresponds to D flat which is 1À059463 times the lowest note of the scale C. The oscillator O is a pulse generator and the dividers are arranged to operate so that the generated pulses are located approximately midway between the driving pulses from the preceding stage. This is necessary to avoid overlap of pulses so that the adding circuits furnish pulses equal in number to the sum of the combined pulses. If each divider is formed of a bi-stable multivibrator, the desired pulse relationship may be obtained by deriving driving pulses for the subsequent divider from one output and the output for forming the tone signals from the other. Furthermore, it is desirable that the generated pulses should have an absolute pulse width equal to that of the master oscillator. This may be achieved by applying the divider outputs to pulse width converter circuits, (see below). As an alternative, the divider circuits may be formed as an assembly of logic circuits, (see below), which functions directly to generate pulses of the same width as the driving pulses. Fig. 3 illustrates the pulses appearing at the first four stages in Fig. 2 and a sum signal fs which would be produced by adding pulses in accordance with the binary number 1À011. This is typical of the form of the signal produced by the arrangement. Although the pulses are correct in number, the irregular spacing produces a subjectively unacceptable tone. To avoid this, the tone signals are applied through further divider stages C 1 , C 2 , C 3 -C 11 having a division factor of at least 2<SP>5</SP> which function to produce final signals in which the pulse regularity is improved, Fig. 12 (not shown). In another arrangement, Figs. 4 and 5 (not shown), the tone signals are formed by subtracting combinations of pulses from the pulse sequence fo emanating from the master oscillator. This arrangement involves pulse cancellation and the Specification discusses certain restraints on the pulse width and delays to ensure perfect pulse cancellation. Miscellaneous musical features; special effects.-The Specification includes the table of binary numbers for establishing the equal tempered scale employed in Fig. 2, and also gives tables for establishing natural and mean tone tuning scales. Reference is also made, but without giving details, to the 31-tone scale. The master oscillator may be arranged for continuous or stepwise adjustment to permit the instrument to be adapted to other instruments or transposed in tuning. A continuous change of tuning may be produced in response to each key operation to produce special effects, for example, the imitation of a Hawaiian guitar. Binary divider, Fig. 6.-A binary divider arranged to produce output pulses of the same duration as input driving pulses comprises an assembly of logic circuits L1-L6, each of which has a number of inputs and an output at which a voltage may occur at a first level if at least one of the voltages at the inputs has a first value, and at a second level if the voltages at the inputs all have a second value. Waveforms throughout the circuit are illustrated in Fig. 7 (not shown). The Specification includes a truth table for the circuit. Pulse width converter circuits.-Pulses appearing at successive stages in a binary dividing chain D 1 , D 2 , D 3 &c. are reduced to equal the width of the pulses applied at the input of the chain. In a first arrangement, Fig. 8, the outputs are applied to logic circuits L 1 -L 4 which receive the input pulses via inverter I and are also interconnected with the output from one circuit being applied to the inputs of all succeeding stages. The circuits have the inputoutput characteristics described above in connection with Fig. 6. Waveforms throughout Fig. 8 are illustrated in Fig. 7 (not shown). In another arrangement, Fig. 10, each divider output triggers a bi-stable circuit B 1 , B 2 , B 3 &c. which is reset by an inverted form of the chain input obtained via inverter I. Waveforms throughout this arrangement are illustrated in Fig. 11 (not shown).