GB1359696A - Musical instruments - Google Patents

Abstract

1359696 Electrical musical instruments CHICAGO MUSICAL INSTRUMENT CO 28 Oct 1971 [30 April 19.71] 50150/71 Heading G5J The harmonic content of a signal during its attack or decay is varied by keying circuits 13, Fig. 1, and is also dependent upon the volume selected. Signal sources 11a to 11n are connected through the keying circuits 13 to conventional formant circuits 16 and audio section 17, 18, 19. The keying circuits each comprise a transistor 26, Fig. 2, and means for determining the attack and decay of the signal, comprising capacitor 36, diode 38 and resistor 37. When a corresponding key 14a is closed on to voltage supply bus-bar 33 the capacitor is charged through resistor 37 and when the key is released the capacitor 36 rapidly discharges through diode 38. Thus a relatively slow attack and fast decay are provided. If the diode is reversed a fast attack and slow decay results as in a piano voice. Due to the action of further capacitor 25 and resistor 34 the transistor does not pass the full duration of the signal pulses arriving at 12a and when key 14a is closed, the charging of capacitor 36 results in not only a rise in the signal amplitude at the transistor collector but also a gradual decrease in the duration of the signal pulses (Fig. 3, not shown). Therefore during the attack the signal fundamental frequency is kept constant but the harmonic content of the signal is gradually altered. The voltage supply bus-bar 33 is also coupled to a circuit 20 (also Fig. 5, not shown) for applying tremolo. The volume control 17 also determines the D.C. voltage on bus-bar 33 and therefore the eventual signal amplitude appearing at the transistor collector. As the signal amplitude and duration are inter-related (Fig. 3, not shown) the volume control therefore also determines the harmonic content of the signal. The various signal sources 11a to 11n are connected to conductors 12a to 12n which are mutually coupled by capacitors 21, 22 &c. the capacitors being provided by discrete components or merely by the close proximity of the conductors to each other. Therefore if, for example, key 14a is pressed not only is the signal from source 11a passed but also, to a lesser extent, the signals from sources 11b to 11n. Due to the decrease in input impedance of corresponding circuit 13 during the attack the mutual coupling effectively gradually decreases and the overall effect is to simulate the attack of a wind instrument.