Page 86 - Master Handbook of Acoustics

FIGURE 4-13 Pitch (in mels, a subjective unit) is related to frequency (in hertz, a physical unit)
according to this curve obtained by juries of listeners. (Stevens and Volkman.)

Researchers tell us that the human ear can detect about 280 discernible steps in intensity and some
1,400 discernible steps in pitch. As changes in intensity and pitch are vital to audio communication, it
would be interesting to know how many combinations are possible. Offhand, it might seem that there

would be 280 × 1,400 = 392,000 combinations detectable by the ear. This is overly optimistic
because the tests were conducted by comparing two simple, single-frequency sounds in rapid
succession and bears little resemblance to the complexities of commonly heard sounds. Other
experiments suggest that the ear can detect only about 7° of loudness and 7° of pitch or only 49 pitch-
loudness combinations. Perhaps not coincidentally, this is not too far from the number of phonemes

(the smallest unit in a language that distinguishes one utterance from another) which can be detected in
a language.