1. A hearing prosthesis comprising: an input signal channel providing a digital input signal in response to acoustic signals from a listening environment, processing means adapted to process the digital input signal in accordance with a predetermined signal processing algorithm to generate a processed output signal, an output transducer for converting the processed output signal into an electrical or an acoustic output signal, the processing means being further adapted to: extract feature vectors, O(t), representing predetermined signal features of consecutive signal frames of the digital input signal, process the extracted feature vectors, or symbol values derived therefrom, with a Hidden Markov Model associated with a predetermined sound source to determine probability values for the predetermined sound source being active in the listening environment, wherein the extracted features vectors represent substantially level independent signal features, or absolute spectrum shape independent signal features, of the consecutive signal frames.