Transformation of a speech signal comprises separating the speech signal into two signal parts (a, b), where (a) represents the quasistationary part and (b) the transient part of the signal. The signal (b) is filtered inversely and is supplied in parallel to a transient detector and a pitch manipulator, while the signal (a) is subjected to a spectral analysis. The transformation circuit of the invention permits well-defined manipulation of any speech signal, which is advantageous partly for hearing-impaired persons, partly for persons having normal hearing ability in noisy environments. Finally, the circuit of the invention has been found to be extremely expedient for synthesizing well-defined sounds, which is of great importance in the control of hearing aids (hearing loss simulator).