Abstract: A sensory aid for the blind in which a frequency swept ultra-sonic carrier signal is generated and radiated as acoustic energy from a head set and reflected acoustic energy is received by two spaced apart receiving transducers which feed a two channel receiver. The receiving transducers have divergent polar lobes which in combination with the polar lobe of the transmitting transducer simulate the characteristics of a normal human auditory system. The carrier signal is multiplied with each received signal to produce respective beat frequency signals each of which have a frequency and level which is dependant on the range and direction respectively of the source of reflection with respect to the user. The gain of both channels is controlled synchronously by controlling the level of the carrier signal multiplied with each received signal. The range of gain control can be increased by feeding the transmitting transducer with the controlled level carrier signal.

Abstract: A gain control and method therefor which allows the use of a single gang variable attenuator for the synchronous control of the gains of each channel of a multi-channel system of the type employing a separate transmission path for each channel. This is accomplished by inserting multipliers at the output of each transmission path and multiplying the path signals with a carrier signal the level of which is varied with a single gang attenuator. The level of the multiplier output signals vary in accordance with the level of the carrier signal. Where intelligence signals are to be inserted at the input of each transmission path these are multiplied with the carrier signal prior to insertion resulting in the recovery of the intelligence signal at the output of the multipliers located at the output of each path. An increased range of gain control can be achieved by inserting the attenuated carrier signal at the inputs of each transmission path.