Perceptual audio coder
Encyclopedia
Perceptual Audio Coder is an algorithm
, like MPEG's MP3
standard, used to compress digital audio
by removing extraneous information not perceived by most people. It is used by Sirius Satellite Radio
for their DARS
service.
The PAC originally developed by Elemedia, a subsidiary of Bell Labs, has a flexible format and bitrate. It provides efficient compression of high-quality audio over a variety of formats from 16 kbit/s for a monophonic channel to 1024 kbit/s for a 5.1 format with four or six auxiliary audio channels, and provisions for an ancillary (fixed rate) and auxiliary (variable rate) side data channel. For stereo audio signals, it is claimed that it provides near compact disc (CD) quality at about 56-64 kbit/s, with transparent coding at bit rates approaching 128 kbit/s. In the 1993, ISO-MPEG-2 5-channel test, PAC demonstrated the best decoded audio signal quality available from any algorithm at 320 kbit/s, far outperforming all algorithms, including the layer-II and layer-III backward compatible algorithms.
Over the years PAC has evolved considerably. A known software implementation of this codec is CelestialTech's AudioLib. Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent. It's available in the AudioVeda music library manager.
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.
The non-capitalized term is used to describe lossy compression codecs that utilize perceptual coding techniques for audio.
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
, like MPEG's MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
standard, used to compress digital audio
Digital audio
Digital audio is sound reproduction using pulse-code modulation and digital signals. Digital audio systems include analog-to-digital conversion , digital-to-analog conversion , digital storage, processing and transmission components...
by removing extraneous information not perceived by most people. It is used by Sirius Satellite Radio
Sirius Satellite Radio
Sirius Satellite Radio is a satellite radio service operating in North America, owned by Sirius XM Radio.Headquartered in New York City, with smaller studios in Los Angeles and Memphis, Sirius was officially launched on July 1, 2002 and currently provides 69 streams of music and 65 streams of...
for their DARS
Digital Audio Radio Service
Digital Audio Radio Service or DARS refers to any type of digital radio service. In the United States it is the official FCC term for digital radio services....
service.
The PAC originally developed by Elemedia, a subsidiary of Bell Labs, has a flexible format and bitrate. It provides efficient compression of high-quality audio over a variety of formats from 16 kbit/s for a monophonic channel to 1024 kbit/s for a 5.1 format with four or six auxiliary audio channels, and provisions for an ancillary (fixed rate) and auxiliary (variable rate) side data channel. For stereo audio signals, it is claimed that it provides near compact disc (CD) quality at about 56-64 kbit/s, with transparent coding at bit rates approaching 128 kbit/s. In the 1993, ISO-MPEG-2 5-channel test, PAC demonstrated the best decoded audio signal quality available from any algorithm at 320 kbit/s, far outperforming all algorithms, including the layer-II and layer-III backward compatible algorithms.
Over the years PAC has evolved considerably. A known software implementation of this codec is CelestialTech's AudioLib. Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent. It's available in the AudioVeda music library manager.
iBiquity
IBiquity
iBiquity Digital Corporation is a company formed by the merger of USA Digital Radio and Lucent Digital Radio, with the goal of creating an in-band on-channel digital radio system for the United States and around the world...
initially tested PAC for the HD-Radio IBOC digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
upgrade for FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
and AM
Amplitude modulation
Amplitude modulation is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent...
, but chose an MPEG4-derived codec, HE-AAC
HE-AAC
High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio...
, instead.
The non-capitalized term is used to describe lossy compression codecs that utilize perceptual coding techniques for audio.