Electronic musical instrument with frequency modulation of a tone signal with an audible frequency signal

Abstract

An electronic musical instrument comprises first and second voltage-controlled frequency-variable oscillators responsive to application of a pitch determining voltage signal from a keyboard circuit to produce first and second audible frequency signals, respectively. The second audible frequency signal is coupled to the first voltage-controlled oscillator to produce a frequency-modulated tone signal to be sounded in which the first audible frequency signal is frequency-modulated with the second audible frequency signal. The content of harmonic components in a musical tone can be increased by sideband components resulting from frequency modulation. The second audible frequency signal may be amplitude-controlled to be proportional, in amplitude, to the magnitude of pitch determining voltage signal, amplitude-modulated with a time-varying control waveform, and/or waveform-modified to provide desirable modulation effects. The mixture of the pitch determining voltage signal and the second audible frequency signal may be coupled to the first voltage-controlled oscillator through an absolute value circuit. The second audible frequency signal may be also coupled to a sound system together with the frequency-modulated tone signal.