Transform coding of audio signals using perceptual noise criteria.

A 4 bit/sample transform coder is designed using a psychoacoustically derived noise masking threshold based on the short-term input spectrum of the signal. The coder has been tested in a formal subjective test involving a wide selection of monophonic audio inputs. The signals used in the test were of 15kHz bandwidth, sampled at 32kHz. The bit rate of the resulting coder was 128kb/s. The subjective test shows that the coded signal could not be distinguished from the original at that bit rate. Subsequent informal work suggests that a bit rate of 96 kb/s may maintain transparency for the set of inputs used in the test.