Audio processing device, system, and method in which frequency bands of an input audio signal are bundled and allocated to channels for processing

The invention relates to a hearing aid comprising a first microphone configured to receive a first acoustic signal and to convert the first acoustic signal to a first electrical audio signal, a speaker configured to emit an acoustic output signal into an ear of a user of the hearing aid device, a first analog-to-digital converter for converting the first electrical audio signal into a first time-domain input signal, a first input unit comprising a first analysis filter bank which is configured to convert the first time-domain input signal to a number NI,1 of first input frequency bands wherein the number NI,1 of first input frequency bands is determined by said first analysis filter bank, a first frequency band bundling and allocation unit which is configured to bundle adjacent first input frequency bands and to allocate first frequency bands to be processed to a number NP,1 of first processing channels, a memory unit which is configured to store data indicating which of the first NI,1 input frequency bands are subject to a likelihood of feedback that is above a threshold, a signal processing unit is configured to process the first frequency bands to be processed in the number NP,1 of first processing channels, and wherein the number NP,1 of first processing channels is smaller than the number NI,1 of first input frequency bands, and wherein the first frequency band bundling and allocation unit is configured to generate a first bundling and allocation scheme which determines the bundling of the first NI,1 input frequency bands and the allocation of the first frequency bands to be processed to the first NP,1 processing channels wherein said first bundling and allocation scheme depends on the likelihood of feedback to occur in at least one of the first NI,1 input frequency bands.