Much of what is done in Simultaneous Masking (see section 3.2)
is based on the existence of
*critical bands*. The hearing works much like a non-uniform
filterbank, and the critical bands can be said to approximate the
characteristics of those filters. Critical bands does not really have
specific ``on'' and ``off'' frequencies, but rather width as a function of
frequency - critical bandwidths.

The parameters for critical bandwidths can be derived in many ways [5]. The critical bandwidths were first derived from the tone masking of white noise. Under the assumption that the tone was masked when the power of the noise in that critical band was equal to the about 1/4 of the power of the tone, critical bandwidth was determined to be

These bandwidths are used to form a critical band scale, rather similar to
the logarithmic musical scale. Conversion between this *Bark* frequency
scale and Hz can be approximated via the function [6]

From here on, *z* will denote frequency in Bark, and *f* frequency in Herz.

Sat Mar 7 16:27:43 PST 1998