Apparatus for testing hearing 100 is arranged to transmit audio tones over the Internet 125 to be output at a receiving station 105, 120 such as a user's computer. The apparatus includes an audio tone store (245, fig. 2) storing each audio tone as a set of two or more components, each component having the same frequency but recorded at different modulation levels. 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. The apparatus also calibrates of the volume of the audible output of the receiving station. A feedback loop is provided where a calibrated audio tone is delivered for output at the receiving station 105, 120 and is transmitted as audible sound back to the hearing test apparatus. The apparatus sends display data to the receiving station representing the sound level of that audible sound, so that a user can adjust the volume of the audible sound at the receiving station to a calibrated level using the display. Alternatively, the apparatus may adjust the receiving station directly, using a Java applet or the like. Calibration can additionally or instead be provided by means of an audio pickup (e.g. a microphone) for measuring and feeding back the level of audio output at user audio delivery equipment (e.g. headphones 115, 110) .
