A method for improving the intelligibility of an incoming telephone
signal, including boosting
loudness of at least one band of poorly heard frequencies of the
signal within at least one band of intensities of the
signal, the band
lying below a predetermined intensity level at which telephone standard
conformance testing is performed, thereby to generate a differentially boosted telephone signal. Alternatively or in addition, intelligibility of sibilants in a
narrow band telephone signal is enhanced, by doubling the sampling rate of the
narrow band signal by interpolation, thereby to provide a
narrow band interpolated signal, generating a
harmonic extrapolation signal by harmonically extrapolating from the narrow band interpolated signal thereby to estimate the missing portions of the telephone signal, the
harmonic extrapolation comprising a sequence of pulses located at peaks of the interpolated signal, generating a missing energy estimator measure estimating energy missing at
high frequency bands of the telephone signal, continuously modulating the amplitude of the pulses in said sequence of pulses based on said missing energy estimator measure, thereby to generate a modulated signal, passing the modulated signal through a shaping filter thereby to obtain a shaped signal, and summing the shaped signal with the interpolated signal.