Audibility of transient intermodulation distortion

The threshold of audibility of TIM distortion was determined for 68 subjects representing all categories of listeners, from musicians and sound engineers to the average man on the street. Three different music samples were used, and controlled amounts of distortion were produced with a digital stereophonic TIM generator. Two basic experimental methods were used to obtain the approximate threshold, after which the reliability of the detection of the distorted passages was verified with a time localization test. The results show that the audibility varies very much depending on the music sample, listening media, and person. The most sensitive group of listeners could reliably perceive 0.5 percent of momentary TIM. Low values of TIM were generally perceived only as slight changes in the tonal character of the sound, and not as distortion. In a number of cases, a preference was found for the slightly distorted sound.