A hearing aid apparatus includes a frequency analysis device configured to determine an instantaneous fundamental frequency value of a speech signal for a time portion of the speech signal. A statistical evaluation device is configured to determine an average fundamental frequency value of the speech signal over several time portions. A hearing aid apparatus further includes a fundamental frequency modifier that is configured to modify the instantaneous fundamental frequency value to a modified fundamental frequency value such that a difference or a quotient of the instantaneous fundamental frequency value is changed to the average fundamental frequency value according to a specific function. Thereby, a frequency range may be modified within which the fundamental frequency value varies. The hearing aid apparatus further includes a speech signal generator that is configured to generate, on the basis of the modified fundamental frequency value, a speech signal modified with regard to the fundamental frequency.