An internal microphone signal of a headphone is filtered by i) a first filter G that, as part of an acoustic noise cancellation, ANC, subsystem, produces an anti-noise audio signal, and ii) a second filter C to produce a feedback audio signal. An estimate of a transfer function of a path S is determined, wherein the path S is from i) an input of a speaker of the headphone to ii) the internal microphone signal. The second filter C is adapted based on the estimate of the transfer function of the path S drives an input of a speaker of the headphone. Other embodiments are also described.