Very low-bit-rate coding requires frequency-domain processing because masking is a spectral phenomenon.

Evidence

Although noise shaping provides a means of psychoacoustically shaping the quantization noise, it is difficult to achieve very low bit rates using it. In particular, one needs to be able to avoid transmitting information in frequency regions that either contain no signal or are masked by other signal components. To do this easily, one must work in the frequency domain. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2672

Categorization

• DEFINE: Clarifies why perceptual coders must move into the frequency domain, grounding the critical-band machinery introduced earlier.