The invention relates to a method of processing an audio signal in a portable listening device, the audio signal comprising a low frequency part having an LF-bandwidth ΔfLF and a high-frequency part having a HF-bandwidth ΔfHF. The invention further relates to a listening device and to a listening system. The object of the present invention is to improve performance or save power in a portable listening device. The problem is solved in that the method comprises a) providing an audio input signal consisting of said low frequency part having an LF-bandwidth ΔfLF; b) performing at least one signal processing step on the low frequency part of the audio signal; and c) performing a bandwidth extension process on said low frequency part of the audio signal to generate said high-frequency part of the audio signal, thereby generating or regenerating said audio output signal with a full bandwidth Δffull comprising said LF-bandwidth ΔfLF and said HF-bandwidth ΔfHF. An advantage of this is that power consumption is reduced. The invention may e.g. be used for portable communication device, mobile telephones or listening devices, such as a hearing aids, ear protection devices, headsets, head phones, etc.