11. The method according to claim 10 , wherein the step of detecting a first dominating frequency and a second dominating frequency in the input signal involves deriving a first notch gradient and a second notch gradient from the input signal.
10. A method of shifting audio frequencies in a hearing aid, said method involving the steps of obtaining an input signal, detecting a first dominating frequency in the input signal, detecting a second dominating frequency in the input signal, shifting a first frequency range of the input signal to a second frequency range of the input signal, superimposing the frequency-shifted first frequency range of the input signal to the second frequency range of the input signal according to a set of parameters derived from the input signal, wherein the step of detecting the first dominating frequency and the second dominating frequency incorporates the step of determining the presence of a fixed relationship between the first dominating frequency and the second dominating frequency, the step of shifting the first frequency range being controlled by the fixed relationship between the first dominating frequency and the second dominating frequency.