GB1506272A - Monophonic electronic musical instrument - Google Patents

Abstract

1506272 Electronic musical instruments HAMMOND CORP 4 March 1975 [4 March 1974] 8928/75 Heading G5J [Also in Division H3] In a monophonic instrument, such as a synthesizer, keys produce control signals on note busses which signals are encoded into a binary word which is stored in a memory, the stored word being used to gate from a tone generator a particular tone signal corresponding to a depressed key. In a complete system (Fig. 2) which is for instance associated with one keyboard 10 of a polyphonic instrument (Fig. 1, not shown), the key switches are coupled by diodes and preference circuits (Fig. 5, not shown) so that one line out of a group of 12 is marked to signal the note name of the higher key operated and one out of a further group of 6 to signal the octave of that note. The 12 and 6 lines respectively are applied to diode matrices which encode the signals to provide a four bit binary number representing the note and three bit number representing the octave; the two numbers are set into 7 bi-stable latches (Fig. 6, not shown). A generator 100 (Fig. 3, not shown) provides a set of top octave frequencies and the four bit number from the latches is decoded (Fig. 4, not shown) to gate an appropriate one of the frequencies to a set of dividers 170. The three bit number is decoded (Fig. 8, not shown) to gate the output from an appropriate one of the dividers to the amplifier and output circuits. The output of the latches is also applied to a D/A converter 230, which comprises seven different constant current generators (Fig. 8, not shown), which produces a voltage uniquely identifying the actuated key. This voltage may be applied by a log. function generator to a voltage controlled oscillator to provide tone signals (not described). The voltage is used to control other functions; the step in the voltage is used to generate a pulse at the start of each new note which may be used to trigger an envelope generator to provide for instance percussive tones. Tones played may also be prolonged after the key is released until the pulse signifies that a new key has been depressed. The direction of the voltage step may also be used to control pitch slide whereby the tone starts above or below the keyed note and slides down or up to it depending on whether it is higher or lower than the last note played. Voltage controlled filter and amplifier arrangements 210, 220 are also described (Figs. 9, 11, not shown). Full circuit details are given for all parts of the system. Specifications 1,506,271 and 1,506273 are referred to.