1. A method of signal processing an input signal in a hearing aid to avoid entrainment, the hearing aid including a receiver and a microphone, the method comprising: using a transform domain adaptive feedback cancellation filter to measure an acoustic feedback path from the receiver to the microphone, including separating an input of the transform domain adaptive feedback cancellation filter to a plurality of eigen components each representing a particular frequency band; analyzing a measure of eigenvalue spread of the plurality of eigen components against a threshold for indication of entrainment of the transform domain adaptive feedback cancellation filter, the threshold being a predetermined constant; and upon indication of entrainment of the transform domain adaptive feedback cancellation filter, modulating adaptation of the transform domain adaptive feedback cancellation filter.