Jump to content

AptX: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
→‎Bit-rate quality of Enhanced aptX: Bitrate CD http://en.wikipedia.org/wiki/Compact_Disc_Digital_Audio#Bit_rate
Line 22: Line 22:


== Bit-rate quality of Enhanced aptX ==
== Bit-rate quality of Enhanced aptX ==
aptX provides high quality coding, and in broadcast applications is suitable for AM, FM, DAB, HD Radio and 5.1. aptX can handle up to 4 stereo pairs of AES3 audio and compress to 1 AES3 stream for transmit. aptX offers either 16-bit, 20-bit or 24-bit resolution. For 16-bit audio, the bitrate for aptX 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 aptX at 56 kbit/s rate provides a quality comparable to [[Compact Disk|CD]].{{Citation needed|date=February 2009}}
aptX provides high quality coding, and in broadcast applications is suitable for AM, FM, DAB, HD Radio and 5.1. aptX can handle up to 4 stereo pairs of AES3 audio and compress to 1 AES3 stream for transmit. aptX offers either 16-bit, 20-bit or 24-bit resolution. For 16-bit audio, the bitrate for aptX 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 aptX at 56 kbit/s rate provides a quality comparable to [[Compact Disk|CD]] {{Citation needed|date=February 2009}} (1,411.2 kbit/s).


== aptX Live ==
== aptX Live ==

Revision as of 13:40, 19 September 2013

AptX
File:Apt-X logo.jpg
Internet media typeaudio/aptx
Developed byCSR plc[1]
Type of formatAudio codec

In digital audio data reduction technology, aptX (formerly apt-X) is a family of proprietary audio codec compression algorithms. 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;[2] its design is based on time domain ADPCM principles and eschews psychoacoustic auditory masking techniques.

aptX 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 aptX in the 1990s, APTX has continued to develop the aptX 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.[3] In addition, aptX codec can be used instead of 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. AptX is supported in high-performance Bluetooth peripherals.[4][5]

Today, both standard aptX and Enhanced aptX are used in APT-branded audio codec hardware, and both ISDN and IP audio codecs from other broadcast equipment makers, including WorldCast Systems, Tieline Technology, AVT, Harris Corporation, BW Broadcast, Digigram, MAYAH, Prodys, and Qbit. An addition to the aptX family in the form of aptX Live, offering up to 8:1 compression, was introduced in 2007;[6] and aptX Lossless, a scalable, adaptive, lossless type audio codec was announced in April, 2009.[7]

aptX was previously named apt-X until acquired by CSR plc in 2010.[8]

Bit-rate quality of Enhanced aptX

aptX provides high quality coding, and in broadcast applications is suitable for AM, FM, DAB, HD Radio and 5.1. aptX can handle up to 4 stereo pairs of AES3 audio and compress to 1 AES3 stream for transmit. aptX offers either 16-bit, 20-bit or 24-bit resolution. For 16-bit audio, the bitrate for aptX 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 aptX at 56 kbit/s rate provides a quality comparable to CD [citation needed] (1,411.2 kbit/s).

aptX Live

aptX Live is a low-complexity audio codec that is specifically designed to maximise digital wireless microphone 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. aptX 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, aptX Live also features techniques that aid connection in situations where the bit error ratio (BER) is excessively high.

aptX Lossless

aptX 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 aptX Lossless and can be dynamically traded against other parameters such as levels of compression and computational complexity. The latency of the aptX Lossless codec can be scaled to as low as 1 ms for 48 kHz sampled audio, depending on the settings of other configurable parameters. aptX 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. aptX 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, aptX 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.

Products implementing the aptX codec

See also

References

  1. ^ http://www.csr.com/products/60/aptx
  2. ^ http://www.ecit.qub.ac.uk/SoCaM/AboutUs/Personnel-static/AcademicStaff/[dead link]
  3. ^ http://www.aes.org/events/35/programmeP2.html
  4. ^ "Soundmatters unveils foxLv2 aptX Bluetooth speaker with $199 price tag". Engadget. Retrieved 2013-02-06.
  5. ^ "Galaxy S III just the latest with apt-X Bluetooth audio". SlashGear. Retrieved 2013-02-06.
  6. ^ http://mixonline.com/news/headline/apt-aptxlive-technology-032607/
  7. ^ http://www.design-reuse.com/news/20519/hd-digital-audio-apt-x-lossless.html/[dead link]
  8. ^ "CSR expands audio expertise with acquisition of APT". 2010-07-28. Retrieved 2013-05-20.
  9. ^ http://www.harmankardon.com/estore/hk/us/products/BT/HARKAR-BT_HK_US
  10. ^ "List Of Apt-X Compatible Devices (transmitters, receivers, etc.)". 2013-05-26. Retrieved 2013-06-28.
  11. ^ http://www.lg.com/us/cell-phone-accessories/lg-HBS730
  12. ^ "http://www.csr.com/sony-xperia-z-ultra". Retrieved 2013-07-24.
Retrieved from "https://en.wikipedia.org/w/index.php?title=AptX&oldid=573642325"