The original version of PAC developed by James Johnston and Anibal Ferreira at AT&T's Bell Labs has a flexible format and bitrate.
For stereo audio signals, it is claimed that it provides near-CD quality at about 56-64 kbit/s, with transparent coding at bit rates approaching 128 kbit/s.
Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent, available in the AudioVeda music library manager.
[citation needed] iBiquity initially tested PAC for the HD-Radio IBOC digital radio upgrade for FM and AM, but chose an MPEG4-derived codec, HE-AAC, instead.
MPEG-2 AAC is substantially similar to the original AT&T PAC algorithm written by Johnston and Ferreira, including the specifics of stereo pair coding, bitstream sectioning, handling of 1 or 2 channels at a time, multiple codebooks responding to the same largest absolute value, and block switching triggers.