Abstract: Apparatus for testing hearing is arranged to deliver audio tones over the Internet to be output at a receiving station such as a user's computer. The apparatus firstly constructs audio tones for transmission out of sets of components recorded at different modulation levels for each frequency. This allows significantly finer control over the sound level of the audio tones at the receiving station than would normally be available at the receiving end. Secondly, the apparatus supports a feedback loop, based on a calibrated audio tone delivered for output at the receiving station and transmitted as audible sound back to the hearing test apparatus via a voice activated modem, the apparatus sending display data to the receiving station representing the sound level of that audible sound such that a user can adjust one or more parameters of the receiving station so as to bring the sound level of the audible sound, indicated by the display data, to a calibrated level.