Expansion circuit for improved stereo and apparent monaural image

摘要

An expander circuit for expanding stereo signals comprises left and right channel variable gain stages whose gain varies in proportion to the amplitude of the control signals fed to the control inputs thereof; and left and right channel expansion control signal providing means for receiving respectively at least portions of the left and right channel signals and feeding expansion control signals to the control inputs of the variable gain stages. These control signals have amplitudes directly proportional to the amplitudes of the signals fed to the inputs of the expansion control signal providing means. The improvement in the circuit is the addition of a signal coupling network for coupling a portion of the left-right channel stereo image producing signal components to the input of the associated expansion control signal providing means and a much smaller porportion thereof to the expansion control signal providing means associated with the other channel. The coupling network responds differently to identical apparent monaural image producing signal components in each channel by feeding a larger proportion thereof to the input of the associated expansion control signal providing means. The coupling network is coupled to points of both amplifier channels which prevent the cross-coupling of a significant portion of the signals in each amplifier channel to the main signal path of the other amplifier channel.