Apt-X
Encyclopedia
The digital audio data reduction technology now known as apt-X is a family of proprietary audio codec
compression algorithms developed by APT Licensing. From March 14, 2009, APT Licensing changed the company's trading identity to APTX. The original algorithm was developed in the 1980s by Dr. Stephen Smyth as part of his Ph.D research at Queen's University Belfast School of Electronics, Electrical Engineering and Computer Science; its design is based on time domain
ADPCM
principles and eschews psychoacoustic masking techniques.
apt-X audio coding was first introduced to the commercial market as a semiconductor product, a custom programmed DSP
integrated circuit with part name APTX100ED, which was initially adopted by broadcast automation equipment manufacturers who required a means to store CD-quality audio on a computer hard disk drive for automatic playout
during a radio show, for example, hence replacing the task of the disc jockey
.
Since introducing the first variant of apt-X in the 1990s, APTX has continued to develop the apt-X suite of audio data compression algorithms, making this intellectual property available as software, firmware and programmable hardware for professional audio
, television and radio broadcast
, and consumer electronics
applications in wireless audio, embedded audio for video, and Audio over IP
. In addition, apt-X codec can displace Sub-Band Codec (SBC), the sub-band coding
scheme for high-quality stereo/mono audio streaming mandated by the Bluetooth SIG for the Advanced Audio Distribution Profile (A2DP) of Bluetooth
, the short-range wireless personal-area network standard.
Today, both standard apt-X and Enhanced apt-X are used in APT-branded audio codec hardware, and both ISDN and IP audio codecs from other broadcast equipment makers, including WorldCast Systems, AVT, Harris Corporation
, BW Broadcast, Digigram, MAYAH, Prodys, and Qbit. An addition to the apt-X family in the form of apt-X Live, offering up to 8:1 compression, was introduced in 2007; and apt-X Lossless, a scalable, adaptive, lossless type audio codec was announced in April, 2009.
channel density in bandwidth-constrained scenarios, such as live performance (a.k.a. Programme Making and Special Events), where the spectrum-efficiency of radio-based devices (wireless microphones, in-ear monitoring, talk-back systems) is becoming a prime operational consideration. apt-X Live offers up to 8:1 compression of 24 bit resolution digital audio streams while maintaining acoustic integrity (approx. 120 dB dynamic range) and ensuring latency of around 1.8 ms at 48 kHz sampling rates. In addition, apt-X Live also features techniques that aid connection in situations where the bit error ratio
(BER) is excessively high.
Coding latency is another scalable parameter within apt-X Lossless and can be dynamically traded against other parameters such as levels of compression and computational complexity. The latency of the apt-X Lossless codec can be scaled to as low as 1 ms for 48 kHz sampled audio, depending on the settings of other configurable parameters. apt-X Lossless performs particularly well against other lossless codecs when the coding latency is constrained to be small, such as 5 ms or less, making it particularly appropriate for delay-sensitive interactive audio applications.
Many lossless codecs possess a low computational overhead compared to well-known lossy codecs, such as MP3
and AAC
. This is particularly important for deeply-embedded audio applications running on low-power mobile devices. apt-X Lossless promotes low computational overhead by dynamically selecting the simplest coding functions for each short segment of audio whilst complying with other operational constraints, such as levels of compression and coding delay. Depending on the settings of other scalable parameters, apt-X Lossless can encode a 48 kHz 16-bit stereo audio stream using only 10 MIPS on a modern RISC processor
with signal processing
extensions. The corresponding decoder represents only 6 MIPS on the same platform.
User metadata and special synchronization data can be incorporated into the compressed format at configurable rates. The latter permits rapid decoder resynchronization in the event of data corruption or loss over communications links where Quality of Service
(QoS) can vary rapidly. Depending on the settings of parameters, decoder resynchronization can occur within 1-2 ms.
Audio codec
All codecs are devices or computer programs capable of coding or decoding a digital data stream or signal.The term audio codec has two meanings depending on the context:...
compression algorithms developed by APT Licensing. From March 14, 2009, APT Licensing changed the company's trading identity to APTX. The original algorithm was developed in the 1980s by Dr. Stephen Smyth as part of his Ph.D research at Queen's University Belfast School of Electronics, Electrical Engineering and Computer Science; its design is based on time domain
Time domain
Time domain is a term used to describe the analysis of mathematical functions, physical signals or time series of economic or environmental data, with respect to time. In the time domain, the signal or function's value is known for all real numbers, for the case of continuous time, or at various...
ADPCM
Adaptive DPCM
Adaptive differential pulse-code modulation is a variant of differential pulse-code modulation that varies the size of the quantization step, to allow further reduction of the required bandwidth for a given signal-to-noise ratio....
principles and eschews psychoacoustic masking techniques.
apt-X audio coding was first introduced to the commercial market as a semiconductor product, a custom programmed DSP
Digital signal processor
A digital signal processor is a specialized microprocessor with an architecture optimized for the fast operational needs of digital signal processing.-Typical characteristics:...
integrated circuit with part name APTX100ED, which was initially adopted by broadcast automation equipment manufacturers who required a means to store CD-quality audio on a computer hard disk drive for automatic playout
Playout
In broadcasting, playout is a term for the transmission of radio or TV channels from the broadcaster into broadcast networks that delivers the content to the audience...
during a radio show, for example, hence replacing the task of the disc jockey
Disc jockey
A disc jockey, also known as DJ, is a person who selects and plays recorded music for an audience. Originally, "disc" referred to phonograph records, not the later Compact Discs. Today, the term includes all forms of music playback, no matter the medium.There are several types of disc jockeys...
.
Since introducing the first variant of apt-X in the 1990s, APTX has continued to develop the apt-X suite of audio data compression algorithms, making this intellectual property available as software, firmware and programmable hardware for professional audio
Professional audio
Professional audio, also 'pro audio', refers to both an activity and a type of audio equipment. Typically it encompasses the production or reproduction of sound for an audience, by individuals who do such work as an occupation like live event support, using sound reinforcement systems designed for...
, television and radio broadcast
Broadcast
Broadcast or Broadcasting may refer to:* Broadcasting, the transmission of audio and video signals* Broadcast, an individual television program or radio program* Broadcast , an English electronic music band...
, and consumer electronics
Consumer electronics
Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...
applications in wireless audio, embedded audio for video, and Audio over IP
Audio over IP
Streaming audio over IP networks is being increasingly used by broadcasting companies, among others, to provide high-quality audio feeds over distance across an IP network such as the Internet. The application is also known as audio contribution over IP in reference to the programming...
. In addition, apt-X codec can displace Sub-Band Codec (SBC), the sub-band coding
Sub-band coding
Sub-band coding is any form of transform coding that breaks a signal into a number of different frequency bands and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals....
scheme for high-quality stereo/mono audio streaming mandated by the Bluetooth SIG for the Advanced Audio Distribution Profile (A2DP) of Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
, the short-range wireless personal-area network standard.
Today, both standard apt-X and Enhanced apt-X are used in APT-branded audio codec hardware, and both ISDN and IP audio codecs from other broadcast equipment makers, including WorldCast Systems, AVT, Harris Corporation
Harris Corporation
Harris Corporation is a Florida-based international communications equipment company that produces wireless equipment, electronic systems, and both terrestrial and spaceborne antennas for use in the government, defense, and commercial sectors. It is also the largest private-sector employer in...
, BW Broadcast, Digigram, MAYAH, Prodys, and Qbit. An addition to the apt-X family in the form of apt-X Live, offering up to 8:1 compression, was introduced in 2007; and apt-X Lossless, a scalable, adaptive, lossless type audio codec was announced in April, 2009.
General bit-rate quality of Enhanced apt-X
apt-X provides high quality coding, and in broadcast applications is suitable for AM, FM, DAB, HD Radio and 5.1. apt-X can handle up to 4 stereo pairs of AES3 audio and compress to 1 AES3 stream for transmit. apt-X offers either 16-bit, 20-bit or 24-bit resolution. For 16-bit audio, the bitrate for apt-X is 384 kbit/s (2-channel), 767 kbit/s (4-channel), 1024 kbit/s (5.1-channel), and 1.28 Mbit/s (5.1 channels plus stereo). APTX's official claim is that apt-X at 56 kbit/s rate provides a quality comparable to CD.General description of apt-X Live
apt-X Live is a low-complexity audio codec that is specifically designed to maximise digital wireless microphoneWireless microphone
A wireless microphone, as the name implies, is a microphone without a physical cable connecting it directly to the sound recording or amplifying equipment with which it is associated...
channel density in bandwidth-constrained scenarios, such as live performance (a.k.a. Programme Making and Special Events), where the spectrum-efficiency of radio-based devices (wireless microphones, in-ear monitoring, talk-back systems) is becoming a prime operational consideration. apt-X Live offers up to 8:1 compression of 24 bit resolution digital audio streams while maintaining acoustic integrity (approx. 120 dB dynamic range) and ensuring latency of around 1.8 ms at 48 kHz sampling rates. In addition, apt-X Live also features techniques that aid connection in situations where the bit error ratio
Bit error ratio
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors....
(BER) is excessively high.
General description of apt-X Lossless
apt-X Lossless supports high-definition audio up to 96 kHz sampling rates and sample resolutions up to 24 bits. The codec optionally permits a "hybrid" coding scheme for applications where average and/or peak compressed data rates must be capped at a constrained level. This involves the dynamic application of a form of "near lossless" coding – but only for those short sections of audio where completely lossless coding cannot respect the bandwidth constraints. Even for those short periods while the "near lossless" coding is active, high-definition audio quality is maintained, retaining audio frequencies up to 20 kHz and a dynamic range of at least 120 dB.Coding latency is another scalable parameter within apt-X Lossless and can be dynamically traded against other parameters such as levels of compression and computational complexity. The latency of the apt-X Lossless codec can be scaled to as low as 1 ms for 48 kHz sampled audio, depending on the settings of other configurable parameters. apt-X Lossless performs particularly well against other lossless codecs when the coding latency is constrained to be small, such as 5 ms or less, making it particularly appropriate for delay-sensitive interactive audio applications.
Many lossless codecs possess a low computational overhead compared to well-known lossy codecs, such as 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...
and AAC
AAC
AAC refers to Advanced Audio Coding, an audio compression format successor to the MP3 format.AAC may also refer to:-Aviation:* AAC, IATA airport code for El Arish International Airport, Egypt...
. This is particularly important for deeply-embedded audio applications running on low-power mobile devices. apt-X Lossless promotes low computational overhead by dynamically selecting the simplest coding functions for each short segment of audio whilst complying with other operational constraints, such as levels of compression and coding delay. Depending on the settings of other scalable parameters, apt-X Lossless can encode a 48 kHz 16-bit stereo audio stream using only 10 MIPS on a modern RISC processor
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
with signal processing
Signal processing
Signal processing is an area of systems engineering, electrical engineering and applied mathematics that deals with operations on or analysis of signals, in either discrete or continuous time...
extensions. The corresponding decoder represents only 6 MIPS on the same platform.
User metadata and special synchronization data can be incorporated into the compressed format at configurable rates. The latter permits rapid decoder resynchronization in the event of data corruption or loss over communications links where Quality of Service
Quality of service
The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...
(QoS) can vary rapidly. Depending on the settings of parameters, decoder resynchronization can occur within 1-2 ms.
See also
- Lossy data compressionLossy data compressionIn information technology, "lossy" compression is a data encoding method that compresses data by discarding some of it. The procedure aims to minimize the amount of data that need to be held, handled, and/or transmitted by a computer...
- Lossless data compressionLossless data compressionLossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. The term lossless is in contrast to lossy data compression, which only allows an approximation of the original data to be reconstructed, in exchange...
- Audio codecAudio codecAll codecs are devices or computer programs capable of coding or decoding a digital data stream or signal.The term audio codec has two meanings depending on the context:...
- ATRACATRACAdaptive Transform Acoustic Coding is a family of proprietary audio compression algorithms developed by Sony. MiniDisc was the first commercial product to incorporate ATRAC in 1992. ATRAC allowed a relatively small disc like MiniDisc to have the same running time as CD while storing audio...
- Sub-band codingSub-band codingSub-band coding is any form of transform coding that breaks a signal into a number of different frequency bands and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals....
External links
- The CSR eXtension Partner Program - BluetoothBluetoothBluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
A2DP apt-X implementation - apt-X overview page - Official site
- Article Skips Second Coding Family, Radio WorldRadio WorldRadio World is a trade journal published by NewBay Media targeted at radio broadcast executives and operations personnel in World Wide. Multiple editions are published for the United states, Canada, Europe, the Middle East, Africa, Asia, and the Caribbean in Spanish, Portuguese and French...
09.12.2007 - Licensable Intellectual Property for HD Digital Audio, Entertainment Engineering, Volume 6, Issue 6