Page 83 - Master Handbook of Acoustics
P. 83
convenience of being calculable from the equation:
FIGURE 4-11 A comparison of bandwidths of 1/3- and 1/6-octave bands, critical bands of the ear,
and equivalent rectangular bandwidth (ERB).
where f = frequency, kHz
One-third-octave filter sets have been justified in certain measurements because the filter
bandwidths approach those of the critical bands of the ear. For comparison, a plot of 1/3-octave
bandwidths is included in Fig. 4-11. One-third-octave bands are 23.2% of the center frequency. The
critical-band function is about 17% of the center frequency. The ERB function is about 12%; this is
close to that of 1/ -octave bands (11.6%). This suggests that 1/6-octave filter sets may be at least as
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relevant as 1/3-octave filters.
Critical bands are important in many audio disciplines. For example, perceptual codecs such as
MP3 and AAC are based on the principle of masking. A tone (a music signal) will mask quantization
noise that lies within a critical band centered at the tone’s frequency. However, if the quantization
