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 shortterm 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 15 kHz bandwidth, sampled at 32 kHz. The bit rate of the resulting coder was 128 kbits/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 kbits/s may maintain transparency for the set of inputs used in the test.