1. Method of evaluating quality of a degraded speech signal received from an audio transmission system, by conveying through said audio transmission system a reference speech signal such as to provide said degraded speech signal, wherein the method comprises: sampling said reference speech signal into a plurality of reference signal frames, sampling said degraded speech signal into a plurality of degraded signal frames, and forming frame pairs by associating said reference signal frames and said degraded signal frames with each other; providing for each frame pair a difference function representing a difference between said degraded signal frame and said associated reference signal frame; compensating said difference function for one or more disturbance types such as to provide for each frame pair a disturbance density function which is adapted to a human auditory perception model; deriving from said disturbance density functions of a plurality of frame pairs an overall quality parameter, said quality parameter being at least indicative of said quality of said degraded speech signal; wherein, said method further comprises the steps of: identifying one or more silent frames of said plurality of degraded signal frames; determine for said silent frames a noise level parameter value indicative of an average amount of signal power which is present in the silent frames at frequencies above a frequency threshold; determining a high band noise level compensation factor based on the noise level parameter value for compensating the overall quality parameter for noise above said frequency threshold.