Quantification of the Noisiness of “Approaching” and “Receding” Sounds

This investigation represents the first phase of a research program designed to quantify subjective responses to time-varying sounds grossly approximating those produced by aircraft flying over an observer at rest. The basic sounds employed represented “approaching” and “receding” sources that continuously increased or decreased in intensity and/or frequency over a period of 15.25 sec. The comparative annoyance or noisiness of such sounds was evaluated by means of paired comparison and individual adjustment judgments. For the three experiments conducted, the findings indicated that: (1) Signals representing an “approaching” sound were generally judged more annoying than those representing a “receding” sound—in spite of the fact that the approaching and receding signals contained the same average intensity and frequency content over signal duration. (2) Signals with time-varying components—whether intensity or frequency—were judged to be noisier than signals with non-time-varying components. The maximum average difference due to time variation of the signal was 17.5 dB. (3) Time-varying intensity components appeared to have a greater influence on judgments of noisiness than did time-varying frequency components. (4) On the average, only small nonsystematic differences in noisiness were found as a function of the three frequency conditions investigated (125-, 1000-, and 4000-Hz-band center frequency).