A circuit for processing an audio signal includes an input stage to which the audio signal is applied and an output at which the processed audio signal is presented. The circuit comprises first and second input stages (11, 12) having nonlinear performance curves, the first stage receiving the audio signal at a specified phase, and the second stage receiving from an inverter (13) an inverse phase of the audio signal. A positive half wave of the input signal is processed nonlinearly and the negative half wave is processed linearly. A difference amplifier (14) receives the signals produced by the first and second input stages and generates an audio signal representing a difference between the signals present at its inputs.