In an exemplary embodiment, for testing the chronological resolution of hearing, acoustic signals are supplied to the ear to be tested via an earpiece and consist of a test tone which can be interrupted and of a masking sound which can be modulated, their frequency and amplitude level being adjustable....http://www.google.fr/patents/US4390748?utm_source=gb-gplus-shareBrevet US4390748 - Electro-acoustical measuring device and method
