Abstract: A method of calculating an objective score (NOS) of the perceived quality of an audio signal degraded by the presence of noise and processed by a noise reducing function, said method comprising a preliminary step of obtaining a predefined test audio signal (x[m]) containing a wanted signal free of noise, a signal (xb[m]) affected by noise obtained by adding a predefined noise signal to the test signal (x[m]), and a processed signal (y[m]) obtained by applying the noise reducing function to the signal (xb[m]) affected by noise. This method includes a step (a5) of measuring distances (dYX(m,b)) between perceived loudness densities calculated for the processed signal (y[m]) and perceived loudness densities calculated for the test signal (x[m]); and a step (a6) of comparing said distances (dYX(m,b)) with masking thresholds (Smasking(m,b)) calculated for the test signal (x[m]) and/or the processed signal (y[m]).