An electronic musical instrument having a plurality of operators for generating audio frequency waveforms and performing frequency modulation thereof. The operator comprises a wave generator, a phase generator, and an amplitude-envelope generator. The phase generator produces phase-angle data on the basis of frequency-number data modulated by ratio-of-frequency data. While the frequency-number data is common to all operators, ratio-of-frequency data varies independently of those applied to the other operators. This enables operators to create rich, dynamic, lifelike sound. One or more operators are provided with feedback loops that are capable of varying the amount of the feedback in response to key touch, etc., thus achieving expressive tone. A pitch-envelope generator is provided with a random-number generator which modulates the pitch envelope in a random manner to more closely simulate a performance on a real musical instrument. Furthermore, the frequency number is adjusted by altering just a few parameters, which makes it possible to carry out temperament easily.