A hearing aid includes a signal path for receiving at least one audio input signal and an autocorrelation index (ACI) estimator (4). The ACI includes a down-sampler for producing a sampling-rate reduced signal of the audio input signal, a sign extractor for extracting a sign signal of the sampling rate reduced signal, a memory and delay for producing and storing delayed versions of the sign signal, a comparator for comparing a subset of the delayed versions of the sign signal with a version of the non-delayed audio input signal, and an averager for averaging the outputs of the comparator to extract delay specific estimates of the audio signal self-resemblance. An autocorrelation estimator obtains an estimated autocorrelation index by determining summarized features from the delay specific estimates of the audio signal self-resemblance. Also disclosed is a method and a computer program for controlling signal processing in a hearing aid.