On the audibility of small changes in the impulse response of a room

So that the analysis of the large amount of information yielded by an echogram of the impulse response may be restricted by comparing different points of the room, investigations have been performed with the object of determining the absolute perceptibility thresholds for audibility of: (1) Discontinuities in reverberant decays, (2) deviations from regularity of a flutter echo, (3) later echos (delayed >or=70 ms after the direct sound). For investigation 1, the decay of a large room (broadcasting studio, church) stimulated by the report of a starting pistol and recorded on magnetic tape was used. For investigations 2 and 3 the reverberation-free report was used for the electroacoustic synthesis of an impulse response. Very small thresholds occur for deviations from regularity of a flutter echo and for late echos whilst discontinuities in a reverberant decay are very hard to perceive.