| 摘要 |
A tone-generating system for an electronic musical instrument of the percussion type is provided wherein an audible tone closely approximating the corresponding tone of a conventional instrument is generated electronically. A single-pole, double-throw switch is actuated by a key to initiate generation of the tone and a tri-level detecting circuit coupled to the switch is utilized to determine which of the three states the switch is in; that is, the two "throws" or positions of the switch which correspond to the released and depressed positions of the key, and the state in which the switch is between the other two positions. By detecting the three states and developing corresponding control signals, counting circuitry may be utilized to determine the intensity with which the key is depressed to enable generation by a read-only memory of digital scaling signals representative of the variations in amplitude of the initiated tone with respect to the intensity with which the key is depressed. An envelope control counter responds to the control signals and a variable rate clock to drive an envelope generating read-only memory to generate a digital envelope signal. A master frequency generator comprising an oscillator and divider circuitry is used to generate a digital pulse train representative of the frequency spectrum of the initiated tone. The digital scaling signal and digital envelope signal are combined in a multiplying digital-to-analog converter to obtain a corresponding composite signal. The composite signal is integrated to improve its analog characteristics and then it is applied to an output gate wherein it modulates the oscillating signal to produce an electrical signal representative of the initiated tone. The composite signal may be filtered and amplified by appropriate circuitry and then audibly reproduced by a loudspeaker. In the multiple-tone embodiments of the invention, multiplexers are utilized to reduce the amount of circuitry duplication and interconnecting wiring.
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