Tuesday, November 8, 2011

Annoying Sounds

To an audiologist or acoustician it is not news that the ear canal has a resonance in the range of human speech, resulting in extra sensitivity in that range. I even remember my acoustics teacher musing about which came first in human evolution, speech with lots of content roughly around the 1kHz range or ears with extra sensitivity in that range (presumably with the advantage that an eardrum embedded in the skull is more protected from the elements).

To an audio engineer, the "midrange" frequencies are the aggressive frequencies. They're the ones you emphasize when your guitar or snare drum is wimpy, and the ones you take out if the mix is too harsh. Bob Katz, in his book Mastering, the Art and the Science, assigns the following negative subjective terms to describe excesses in this frequency range: boxy (400-900 Hz), nasal (700-1.2 kHz), harsh (2-10 kHz). My 21 year old acoustics text book states, "Noise with appreciable strength around 1000 to 2000 Hz is more disruptive than is low frequency noise."

Because the ear has different sensitivities to different frequencies, different "weightings" have been developed which allow measurements of sound level which take frequency into account. Some municipalities even take these weightings into account for noise complaints. These weightings date back as far as 1936.

Recently, musicologists studied what sounds are annoying. Their findings reenforce this old tale: sounds in the range from 2-4 kHz can be offensive. Even quiet sounds, like the classic fingernails across the chalk-board can be explained by a dominance of sound at these frequencies. What is interesting about this research is that it shows, for the first time as far as I know, that sounds can be made less annoying simply because of context. For example, if the listener is told the source of the sound is fingernails on chalk, they are more likely to say they found it offensive, than if they are told it is a part of a composition. Of course, it's possible they are just being polite, since either way, they have the same biological reaction.

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