A detuning control circuit is provided for producing a pitch variation effect in an electronic musical instrument. The instrument includes at least one integrated circuit tone generator chip (12) having at least one tone generator and a detuning circuit responsive to a predetermined detuning control signal for detuning the signals produced by the tone generator. The detuning control circuit comprises a detuning control signalling circuit (38, 40) for producing a predetermined detuning control signal and for selectively applying the predetermined detuning control signal to the detuning circuit of the tone generator chip so as to produce a predetermined pitch variation effect.