Very low bit rates require working in the frequency domain to skip masked regions

Evidence

Although noise shaping provides a means of psy­ choacoustically shaping the quantization noise, it is difficult to achieve very low bit rates using it. In particular one needs to be able to avoid transmit­ ting 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 Howard, Jamie Angus, coustics and Psychoacoustics, 2669