Abstract: Method and processing system for measuring the intelligibility of a degraded output signal (Y(t)) from an audio transmission system (10) in response to a reference input signal (X(t)). A measurement device (11) is arranged for outputting a measure (I) for the speech intelligibility of the output signal (Y(t)). The measurement device (11) executes processing of the input signal (X(t)) and output signal (Y(t)) to obtain a disturbance density function (D(f)n). The disturbance density function (D(f)n) is corrected by multiplying it with a correction function for each frame derived from a correlation calculation of the compensated pitch power densities (PPX?(f)n) associated with the input signal (X(t)) of a present frame (n) and an independent previous frame (n?2). The corrected disturbance density function (D?(f)n) is aggregated over frequency and time to obtain a measure (I) for the speech intelligibility of the output signal (Y(t)).