Chapter One: An Acoustics Primer
15. What is loudness? | page 2
We had seen earlier that lower frequencies may mask higher frequencies on the basilar membrane, but the complete picture also involves amplitude. Masking occurs when the neurons of the basilar membrane fatigue, and sensitivity to a particular frequency in the critical band of the neurons decreases. As a result, a louder tone may mask a softer tone. The amplitude difference necessary to create masking depends on the frequency difference. The strongest masking response occurs with tones within the same critical band, where the least difference in intensity is required. It is also possible for sounds which are not simultaneous to exhibit masking, if the first tone is sufficiently loud and the subsequent tone occurs within a time span short enough for the neurons to stay fatigued. An extreme example of this might be how many bars of the 1812 Overture you miss following the cannon blast. Masking is yet one more psychoacoustic phenomenon a composer can take advantage of.
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