A method of adjusting frequency-dependent amplification in an audio amplification apparatus. The audio amplification apparatus includes a forward transfer path (2) connectable to an output transducer, the forward transfer path including a frequency transposing element. The method includes the steps of: presenting stimuli to the output transducer at a plurality of frequencies; adjusting the stimulus level (C) at each frequency to meet a predefined loudness perception level or detection threshold of the listener; deriving an equal loudness contour of output transducer levels from the adjusted stimuli levels; and deriving the frequency-dependent amplification of levels of input signals (I) at each frequency.