A noise cancellation signal is generated by generating an ambient noise signal, representing ambient noise, and generating a noise cancellation signal, by applying the ambient noise signal to an feedforward filter, where the feedforward filter comprises a high-pass filter having an adjustable cut-off frequency, and by applying a controllable gain. The noise cancellation signal is then applied to a loudspeaker, to generate a sound to at least partially cancel the ambient noise. An error signal is generated, representing unwanted sound in the region of the loudspeaker. The phase of the ambient noise signal is compared to a phase of the error signal, and the gain is controlled on the basis of a result of the comparison, taking account of a phase shift introduced by the high-pass filter when performing the comparison.