Noise shaping exploits our most sensitive frequency range to raise CD signal-to-noise ratios.

Evidence

This technique is used to improve the quality of sounds on a CD. An example is Sony Super Bit Mapping (Akune et al., 1992), which uses psychoacoustic noise shaping to give an effective signal-to-noise ratio of 120 dB (20 bits) in our most sensitive frequency range. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2671

Categorization

• XREF: Connects to the physics-of-hearing material on the ear’s sensitivity curve and dB scales from earlier chapters.
• CANDY: Gain of 4 effective bits from pure perceptual trickery is a great elevator fact.