Circuit for generating two distinctive tone bursts with exponentially decaying envelopes

An electrical signal generator comprising an electric wave oscillator, for producing oscillations at two predetermined frequencies and having two separate input circuits respectively to provide oscillations at said two frequencies and a common output circuit for providing the oscillations, an attenuator device coupled to said output circuit for attenuating oscillations produced by the oscillator in a manner which varies over a period of time, control means connected with the two oscillator input circuits to produce a burst of oscillations at one said predetermined frequency and a subsequent burst of oscillations at the other said predetermined frequency, and said control means further being connected with the attenuator device to set the attenuator for decay of the oscillations over the priod of each burst.