Psychoacoustic models evolve because encoders are unconstrained by decoders

Evidence

The psychoacoustic quantization block is now replaced by a bit allocation and quantization block, which is driven by a psychoacoustic model that allocates the number of quantization levels for each frequency band, including 0 for no bits allocated. Psychoacoustic models can be quite complicated and are continuously evolving. This is because most lossy audio coding systems define how the receiver interprets the bit stream to form the audio output but leave how those bits are FIGURE 7. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 2674