Tone generator for an electronic musical instrument

A tone generator for an electronic musical instrument, the instrument including a plurality of keys which may be actuated to produce input signals, said tone generator comprising:

• means for scanning the keys of the instrument and for producing a numerically coded signal identifying the musical note allocated to each key which is actuated;
• first memory means, said first memory means having a plurality of memory locations, said memory locations being less in number than the number of instrument keys and being equal in number to the number of notes which may be played at one time;
• second memory means, said second memory means having memory locations equal in number to said first memory means;
• means for loading into the memory locations of said first memory means the numerically coded signals commensurate with actuated keys;
• clock pulse generator means;
• counter means, said counter means being responsive to clock pulses produced by said clock pulse generator means, said counter means having a capacity equal in number to the memory locations in said memory means;
• multiplexor means connected to said counter means and said second memory means for simultaneously decrementing the numerically coded signals stored in each of said second memory means memory locations;
• means for transferring numerically coded signals stored in said first memory means into corresponding memory locations in said second memory means whenever the said corresponding memory location in said second memory means has been cleared by being counted down to zero;
• means responsive to each clearing of a memory location in said second memory means for generating a trigger signal;
• and
• sweep voltage generator means responsive to said trigger signal for generating a polyphonic signal in the audible frequency range.