Each frequency band has a scale factor associated with it. You can
think of it as an extra boost or cut to the energy of a part of the
signal. The default setting is 1.0 (no change).
The outer iteration loop communicates to the scale factor section
the amount of quanitized noise for each band, if this exceeds a masking
threshold (from the Perceptual Model) the scale factor is adjusted
to reduce the quanitization noise.