<p>The reduction of distortion introduced by a loudspeaker is shown. An ultrasound generator (408) generates an ultrasound signal. A signal processor is configured to process an input signal to produce a modulating signal and to modulate the ultrasound signal to produce a modulated ultrasound signal. A combiner (403) combines the input signal with the modulated ultrasound signal to produce an output signal. The signal processor includes means (406) for calculating absolute values and inverting means (407) for inverting the absolute values to produce the modulating signal.</p>
