View source for AptX

{{Short description|Family of proprietary audio codecs owned by Qualcomm}}
{{lowercase title}}
{{Infobox file format
| name = aptX
| icon = [[Image:QC_aptX_Vertical_Black_4754.png|200px]]
| extension = 
| mime = 
| owner = [[Company:Qualcomm|Qualcomm]]<ref>{{cite web
 | url=http://www.csr.com/products/aptx
 | title=aptX Bluetooth Music Audio Codec
 | publisher=[[Company:CSR plc|CSR plc]]
 | access-date=2016-07-23
 | archive-date=2016-07-25
 | archive-url=https://web.archive.org/web/20160725101615/http://www.csr.com/products/aptx
 | url-status=dead
 }}</ref><ref>{{cite web
 | url=http://www.aptx.com/about-aptx
 | title=About aptX
 | access-date=2016-07-23}}</ref>
| genre = [[Audio codec]]
| container for = 
| contained by = 
| extended from = 
| extended to = 
| standard = 
| url = 
}}

'''aptX''' (''apt'' stands for ''audio processing technology''<ref name="mixonline.com"/>) is a family of [[Proprietary software|proprietary]] [[Audio codec|audio codec]] compression algorithms owned by [[Company:Qualcomm|Qualcomm]], with a heavy emphasis on wireless audio applications.

==History==
The original compression algorithm was developed in the 1980s by Dr. Stephen Smyth as part of his [[Ph.D.]] research at [[Organization:Queen's University Belfast|Queen's University Belfast]] School of Electronics, Electrical Engineering and Computer Science<ref name="irishtimes">{{cite web | url=https://www.irishtimes.com/business/adventure-ends-for-local-management-team-who-took-on-big-boys-1.632069 | title=Adventure ends for local management team who took on big boys | website = irishtimes.com | date=2010-08-03 | access-date=2019-09-30}}</ref> its design is based on [[Time domain|time domain]] ADPCM principles without psychoacoustic [[Physics:Auditory masking|auditory masking]] techniques.

The algorithm was then commercialized under the name aptX and first introduced to the commercial market as a semiconductor product, a custom programmed [[Engineering:Digital signal processor|DSP]] integrated circuit with part name APTX100ED, which was initially adopted by [[Engineering:Broadcast automation|broadcast automation]] equipment manufacturers who required a means to store CD-quality audio on a computer [[Engineering:Hard disk drive|hard disk drive]] for automatic [[Engineering:Playout|playout]] during a radio show, for example, hence replacing the task of the [[Disc jockey|disc jockey]].

The company was bought by [[Company:Solid State Logic|Solid State Logic]] ca. 1988, and became part of Carlton Communications plc.<ref>{{cite web | url = https://www.referenceforbusiness.com/history2/92/Carlton-Communications-PLC.html | title = Company profile and background information on Carlton Communications PLC | access-date = 2021-11-25 | archive-date = 2019-09-28 | archive-url = https://archive.today/20190928175142/https://www.referenceforbusiness.com/history2/92/Carlton-Communications-PLC.html | url-status = bot: unknown }}</ref> in 1989. In the early 1990s, APT's codecs were used to transfer audio via ISDN lines<ref>{{cite web | url = https://www.aptx.com/history | title = History of aptX | website = aptx.com | archive-url = https://archive.today/20190928162749/https://www.aptx.com/history | archive-date = September 28, 2019 | url-status = live | access-date = September 28, 2019 }}</ref><ref>{{cite web | url = http://www.digifon.com/Blog041.html | title = About APT-X | access-date = September 28, 2019 | archive-date = September 28, 2019 | archive-url = https://archive.today/20190928170004/http://www.digifon.com/Blog041.html | url-status = dead }} The author is a member of the Audio Engineering Society ([https://archive.today/20190928165646/https://www.google.com/search?q=%22dave+immer%22&oq=%22dave+immer%22&aqs=chrome..69i57j0l4j69i60.2431j0j4&sourceid=chrome&ie=UTF-8%23spf=1569689799547 aes.org])</ref> by companies such as [[Company:The Walt Disney Company|Disney]] to check dubbing done in Europe. On 23 December 1999,<ref>{{cite web | url = https://www.theguardian.com/business/1999/dec/23/2 | title = BA cuts stake in Equant | website = TheGuardian.com | date = December 23, 1999 | archive-url = https://archive.today/20190928190655/https://www.theguardian.com/business/1999/dec/23/2 | archive-date = September 28, 2019 | url-status = live | access-date = September 28, 2019 }}</ref> Solid State Logic was sold by Carlton Communications to 3i.<ref>{{cite web | url =https://variety.com/1999/biz/news/carlton-sells-solid-state-arm-1117760329/#! | title = Carlton sells Solid State arm | publisher = variety.com | archive-url = https://archive.today/bPQnQ/ | archive-date = September 28, 2019 | url-status = live}}</ref><ref>{{cite web | url = https://www.gracesguide.co.uk/Carlton_Communications | title = Carlton Communications | publisher = Grace's Guide }}</ref>  Then in 2005, Solid State Logic sold APT in a management buyout.<ref name="irishtimes" /><ref name="mixonline.com">{{cite web | url = https://www.mixonline.com/technology/solid-state-logic-sells-apt-381257 | title = Solid State Logic Sells APT (Audio Processing Technology) | date = May 12, 2005 | website = mixonline.com }}</ref> On 1 March 2005 APT Licensing Ltd. was incorporated in [[Place:Belfast|Belfast]] (until 18 December 2008 named ''Audio Processing Technology Holdings Limited'').<ref>[https://beta.companieshouse.gov.uk/company/NI054094 APT Licensing Limited] on ''Companies House''</ref>

The range of aptX algorithms for real-time audio data compression expanded with intellectual property becoming available in the form of software, firmware and programmable hardware for [[Engineering:Professional audio|professional audio]], television and radio broadcast, and [[Engineering:Consumer electronics|consumer electronics]], especially applications in wireless audio, low latency wireless audio for gaming and video, and [[Audio over IP|audio over IP]].<ref>{{cite web
| url=http://www.aes.org/events/35/programmeP2.html
| title=Programme, Thursday 12th February
| publisher=Audio Engineering Society
| date=2009-02-12
| access-date=2016-07-23}}</ref> In addition, the aptX codec was introduced as an alternative to [[SBC (codec)|SBC]], the [[Sub-band coding|sub-band coding]] scheme for lossy 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.<ref>{{cite web
| url=https://www.engadget.com/2012/12/04/soundmatters-foxlv2-aptx-bluetooth-speaker/
| title=Soundmatters unveils foxLv2 aptX Bluetooth speaker with $199 price tag
| author=Alexis Santos
| date=2012-12-04
| publisher=[[Software:Engadget|Engadget]]
| access-date=2016-07-23}}</ref><ref>{{cite web
| url=http://www.slashgear.com/galaxy-s-iii-just-the-latest-with-apt-x-bluetooth-audio-04226274/
| title=Galaxy S III just the latest with apt-X Bluetooth audio
| author=Chris Burns
| date=2012-05-04
| publisher=slashgear.com
| access-date=2016-07-23}}</ref>

Today, standard aptX and Enhanced aptX (E-aptX) are used in both ISDN and IP audio codec hardware from numerous broadcast equipment makers. An addition to the aptX family in the form of aptX Live, offering up to 8:1 compression, was introduced in 2007;<ref>{{cite web
| url=http://www.mixonline.com/news/news-products/apt-introduce-apt-x-live-nab-2007/382763
| title=APT to Introduce apt-X Live at NAB 2007
| publisher=mixonline.com
| date=2007-03-26
| access-date=2016-07-23}}</ref> and aptX HD, a lossy, but scalable, adaptive, "near-lossless" quality audio codec was announced in April 2009.<ref>{{cite web
 |url=http://www.design-reuse.com/news/20519/hd-digital-audio-apt-x-lossless.html/ 
 |title=APTX elevates HD digital audio with apt-X Lossless 
 |date=2009-04-20 
 |access-date=2016-07-23 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20120508222925/http://www.design-reuse.com/news/20519/hd-digital-audio-apt-x-lossless.html 
 |archive-date=2012-05-08 
}}</ref>

The company split in 2009; the broadcast hardware business was acquired by Audemat and became part of what is now WorldCast Systems, and the licensing business became APT Licensing and was acquired by [[Company:CSR plc|CSR plc]] in 2010.<ref>
{{cite web
| url=http://www.radioworld.com/article/apt-x-coding-developer-acquired-by-csr/4801
| title=apt-X Coding Developer Acquired by CSR
| date=2010-07-28
| publisher=Radio World
| access-date=2016-07-24
| archive-url=https://web.archive.org/web/20160603063742/http://www.radioworld.com/article/apt-x-coding-developer-acquired-by-csr/4801
| archive-date=2016-06-03
| url-status=dead
}}
</ref> aptX was previously styled '''apt-X''' until acquired by CSR in 2010. CSR was subsequently acquired by Qualcomm in August 2015.<ref>{{cite web
| url=https://www.qualcomm.com/news/releases/2015/08/13/qualcomm-completes-24-billion-acquisition-csr
| title=Qualcomm Completes $2.4 Billion Acquisition of CSR
| date=2015-08-13
| publisher=[[Company:Qualcomm|Qualcomm]]
| access-date=2016-07-24
| archive-date=2016-10-17
| archive-url=https://web.archive.org/web/20161017064738/https://www.qualcomm.com/news/releases/2015/08/13/qualcomm-completes-24-billion-acquisition-csr
| url-status=dead
}}</ref>

==Variants==
{|class="wikitable" style="text-align:center"
|+aptX variants<ref name="main source">[https://www.qualcomm.com/products/features/aptx ''aptX Adaptive product brief'' with comparison table] (linked pdf)</ref>
! rowspan="2" colspan="2" style="border-bottom:2px solid gray; background-color:#D8D9DD" | 
! style="border-bottom:hidden; background-color:#D8D9DD" | [[SBC (codec)|SBC]]
! style="border-bottom:hidden; background-color:#D6F9D6" | aptX
! style="border-bottom:hidden; background-color:#D6F9D6" | aptX LL
! style="border-bottom:hidden; background-color:#D6F9D6" | aptX HD
! style="border-bottom:hidden; background-color:#D6F9D6" colspan="2" | aptX Adaptive
! style="border-bottom:hidden; background-color:#D8D9DD" | [[Company:Compact Disc Digital Audio|Audio CD]]
|-
! style="background-color:#D8D9DD; border-bottom:2px solid gray" | 
! style="background-color:#D6F9D6; border-bottom:2px solid gray" | 
! style="background-color:#D6F9D6; border-bottom:2px solid gray" | 
! style="background-color:#D6F9D6; border-bottom:2px solid gray" | 
! style="background-color:#D6F9D6; border-bottom:2px solid gray; font-weight:lighter" | @&nbsp;279kbit/s
! style="background-color:#D6F9D6; border-bottom:2px solid gray; font-weight:lighter" | @&nbsp;420 kbit/s
! style="background-color:#D8D9DD; border-bottom:2px solid gray" | <small>(for reference)</small>
|-
! rowspan="6" | misc.
! style="text-align:left" | Launch
| style="background-color:#F0F2F6" | '''?'''
| '''< 2009'''<ref name="Qualcomm history">[https://www.aptx.com/history History of aptX]: ''[[Company:Sennheiser|Sennheiser]] launched the first ever Bluetooth headset with aptX.''</ref> || '''2012'''<ref>[http://www.rayson.com/rayson/en/?pros=product&pros=product&b_cat_id=A01&m_cat_id=A0102&s_cat_id=A010207&prod_id=P0031&level=3 Rayson BTM-770G]: One of the first products with Qualcomm Chip CSR8670 and aptX LL</ref> || '''2016'''<ref name="Qualcomm history"/> || colspan="2" | '''2018'''<ref name="Qualcomm history"/>
| style="background-color:#F0F2F6" | '''1980s'''
|-
! style="text-align:left" | [[Social:Trademark|Trademark]]
| style="background-color:#F0F2F6" | –
| colspan="5" | [[Company:Qualcomm|Qualcomm]]<br><small>(until August 2015: [[Company:CSR|CSR]], until July 2010: APT Licensing Ltd., until March 2005: [[Company:Solid State Logic|Solid State Logic]])</small> || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | Related [[Social:Patent|patent]]s
| style="background-color:#F0F2F6" | {{patent|EP|0400755B1}}<ref name=ep0400755B1>J.B. Rault, Y.F. Dehery, J.Y. Roudaut, A.A.M. Bruekers, R.N.J. Veldhuis, "Digital transmission system using subband coding of a digital signal", Publication number: {{patent|EP|0400755B1}}</ref> (expired) || {{patent|EP|0398973B1}}<ref name=ep0398973B1>S.M.F. Smyth, "Method and apparatus for electrical signal coding", Publication number: {{patent|EP|0398973B1}}</ref> (revoked) || aptX,<br> {{patent|US|9398620B1}}<ref name=US9398620B1 >J.J. Lazzeroni, M.K. Carevich, J.D. Vertz, P.E.H. Hauser, S.J. Kingston, "Simultaneous voice and audio traffic between two devices on a wireless personal-area network", Publication number: {{patent|US|9398620B1}}</ref> (expired) || aptX || colspan="2" | ? || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | [[Free software|Free implementations]]
| style="background-color:#F0F2F6" | BlueZ libsbc<br>[[Software:PulseAudio|PulseAudio]], [[Software:PipeWire|PipeWire]] || [[Software:FFmpeg|FFmpeg]], libopenaptx, [[Software:PulseAudio|PulseAudio]], [[Software:PipeWire|PipeWire]] || [[Software:FFmpeg|FFmpeg]], libopenaptx, [[Software:PipeWire|PipeWire]] || [[Software:FFmpeg|FFmpeg]], libopenaptx, [[Software:PulseAudio|PulseAudio]], [[Software:PipeWire|PipeWire]] || colspan="2" | N/A || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | [[Proprietary software|Proprietary implementations]]
| style="background-color:#F0F2F6" | Multiple || Qualcomm libaptX<ref name="aosp-aptx">[https://android.googlesource.com/platform/system/bt/+/3a3ec66a1bb7f5c99b17239021d6d184a3abd4ee%5E%21/ Integration of the aptX and aptX-HD codecs for A2DP source], Android Open Source Project, January 4, 2017</ref> || None || Qualcomm libaptXHD<ref name="aosp-aptx" /> || colspan="2" | ? || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | Chip
| style="background-color:#F0F2F6" | –
| CSR8635 || CSR8670 || CSR8675 || colspan="2" | QCC5100 || style="background-color:#F0F2F6" | –
|-
! rowspan="8" | Audio<br>Encoding
! style="text-align:left" | [[Audio bit depth|Word depth]]
| style="background-color:#F0F2F6" | '''?'''
| '''16-bit''' || '''16-bit''' || '''16-bit'''<br>'''24-bit''' || colspan="2" | '''24-bit''' || style="background-color:#F0F2F6" | '''16-bit'''
|-
! style="text-align:left" | [[Sampling rate]]
| style="background-color:#F0F2F6" | 44.1&nbsp;kHz<br>48&nbsp;kHz<br>&nbsp; || 44.1&nbsp;kHz<br>48&nbsp;kHz<br>&nbsp; || 44.1&nbsp;kHz<br>48&nbsp;kHz<br>&nbsp; || 44.1&nbsp;kHz<br>48&nbsp;kHz<br>&nbsp; || colspan="2" | 44.1&nbsp;kHz<br>48&nbsp;kHz<br>96&nbsp;kHz || style="background-color:#F0F2F6" | 44.1&nbsp;kHz<br><br>&nbsp;
|-
! style="text-align:left" rowspan="2" | [[Bit rate]]
| style="background-color:#F0F2F6" | '''345 kbit/s''' <small>(@ 48&nbsp;kHz)</small> || '''325 kbit/s''' <small>(@ 44.1&nbsp;kHz)</small><br>'''384 kbit/s''' <small>(@ 48&nbsp;kHz)</small> || '''352 kbit/s''' <small>(@ 48&nbsp;kHz)</small> || '''576 kbit/s''' <small>(24 bits @ 48&nbsp;kHz)</small> || '''279 kbit/s''' || '''420 kbit/s''' || style="background-color:#F0F2F6" | '''1411 kbit/s''' <small>(@ 44.1&nbsp;kHz)</small>
|-
| style="background-color:#F0F2F6" | Constant || Constant || Constant || Constant || colspan="2" | Variable || style="background-color:#F0F2F6" | Constant
|-
! style="text-align:left" | Codec Latency
| style="background-color:#F0F2F6" | ?
| 1.8 – 2.0 ms || ? || 1.8 – 2.0 ms || colspan="2" | 1.4 – 2.0 ms || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | Hardware transmitter [[Engineering:Latency (audio)|latency]]
| style="background-color:#F0F2F6" | ? || ? || '''≈ 40 ms'''<ref name=aptx-ll>{{cite web
  | title = Qualcomm aptX Low Latency Synchronised Audio
  | url = https://www.aptx.com/aptx-low-latency
  | access-date = 6 April 2021
}}</ref><br><small>(using dedicated antenna)</small> || ? || colspan="2" | '''≈ 80 ms'''<ref name=aptx-adaptive>{{cite web
  | title = Qualcomm aptX Adaptive Audio Codec Technology
  | url = https://www.aptx.com/aptx-adaptive
  | access-date = 6 April 2021
}}</ref> || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | Software transmitter [[Engineering:Latency (audio)|latency]] <small>(most&nbsp;phones)</small>
| colspan="6" | '''200 – 500 ms'''<ref name=android-latency>{{Cite web|url=https://www.soundguys.com/android-bluetooth-latency-22732/|title=Android's Bluetooth latency needs a serious overhaul|date=March 6, 2021|website=SoundGuys}}</ref><br><small>depending on the transmitting device</small> || style="background-color:#F0F2F6" | –
|-
! style="text-align:left" | Backwards compatible with
| style="background-color:#F0F2F6" | –
| SBC || SBC, aptX || SBC, aptX || colspan="2" | SBC, aptX, aptX HD || style="background-color:#F0F2F6" | ?
|-
! rowspan="7" | Sound<br>quality
! style="text-align:left" | THD+N @ 1&nbsp;kHz
| style="background-color:#F0F2F6" | 
| −67&nbsp;dB<ref name="Qualcomm aptX">{{Cite web|url=https://www.aptx.com/aptx|title=Qualcomm® aptX™ Audio &#124; Wireless Audio Technology & Products|website=www.aptx.com}}</ref> or −85&nbsp;dB?<ref name="main source"/> || −85&nbsp;dB || -80&nbsp;dB<ref name="Qualcomm aptX HD">{{Cite web|url=https://www.aptx.com/aptx-hd|title=Qualcomm® aptX™ HD &#124; High Resolution Audio Technology|website=www.aptx.com}}</ref> or −90&nbsp;dB?<ref name="main source"/> || −90&nbsp;dB || −100&nbsp;dB || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | Multi-tone @ 1&nbsp;kHz
| style="background-color:#F0F2F6" | 
| −100&nbsp;dB || ? || −100&nbsp;dB || −90&nbsp;dB || −100&nbsp;dB || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | Multi-tone @ 10&nbsp;kHz
| style="background-color:#F0F2F6" | 
| −65&nbsp;dB || ? || −90&nbsp;dB || −85&nbsp;dB || −95&nbsp;dB || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | [[Crosstalk]]
| style="background-color:#F0F2F6" | 
| −120&nbsp;dB || ? || −155&nbsp;dB || −90&nbsp;dB || −200&nbsp;dB || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | [[Physics:Signal-to-noise ratio|SNR]] @ 1&nbsp;kHz
| style="background-color:#F0F2F6" | 
| 93&nbsp;dB || 93&nbsp;dB || 129&nbsp;dB || 130&nbsp;dB || 135&nbsp;dB || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | [[Perceptual Evaluation of Audio Quality|PEAQ]] ODG
| style="background-color:#F0F2F6" | 
| −0.18<ref name="Qualcomm aptX"/> or −0.08?<ref name="main source"/> || ? || 0.05<ref name="Qualcomm aptX HD"/> or 0.04?<ref name="main source"/> || −0.06 || 0.045 || style="background-color:#F0F2F6" | 
|-
! style="text-align:left" | [[Frequency response]] over BT
| style="background-color:#F0F2F6" | 
| 20&nbsp;Hz – 22.7&nbsp;kHz || 20&nbsp;Hz – 22.7&nbsp;kHz || 20&nbsp;Hz – 22.7&nbsp;kHz || colspan="2" | 20&nbsp;Hz – 22.7&nbsp;kHz || style="background-color:#F0F2F6" | 
|}

===aptX===
The aptX audio codec is used for consumer and automotive wireless audio applications, notably the real-time streaming of lossy stereo audio over the Bluetooth A2DP connection/pairing between a "source" device (such as a smartphone, tablet or laptop) and a "sink" accessory (e.g. a Bluetooth stereo speaker, headset or headphones). The technology must be incorporated in both transmitter and receiver to derive the sonic benefits of aptX audio coding over the default sub-band coding (SBC) mandated by the Bluetooth standard. Products bearing the CSR aptX logo are certified for interoperability with each other.<ref>{{Cite web|url=https://www.aptx.com/aptx|title=Qualcomm aptX Audio|website=www.aptx.com|access-date=2019-09-22}}</ref>

===Enhanced aptX===
''Enhanced aptX'' provides coding at 4:1 compression ratios for professional audio broadcast applications and is suitable for AM, FM, DAB, HD Radio and 5.1. Enhanced aptX can handle up to 4 stereo pairs of AES3 audio and compress to 1 AES3 stream for transmit. Enhanced aptX supports bit-depths of 16, 20 or 24 bit. For audio sampled at 48&nbsp;kHz, the bit-rate for E-aptX is 384 kbit/s (dual channel), 768 kbit/s (quad channel), 1024 kbit/s (5.1-channel), and 1280 kbit/s (5.1 channels plus stereo). Its lowest bit-rate is 60(?) kbit/s for mono audio sampled at 16&nbsp;kHz, offering about 7.5&nbsp;kHz frequency response just below that of wideband telephony codecs (which usually operate at 16&nbsp;kHz sampling rate).<ref>{{cite web
| url=http://www.csr.com/products/58/aptx-enhanced
| title=aptX Enhanced
| publisher=[[Company:CSR plc|CSR plc]]
| access-date=2016-07-24}}</ref>

===aptX Live===
''aptX Live'' is a low-complexity audio codec that is specifically designed to maximise digital [[Engineering:Wireless microphone|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&nbsp;dB dynamic range) and ensuring latency of around 1.8 ms at 48&nbsp;kHz sampling rates. In addition, aptX Live also features techniques that aid connection in situations where the [[Bit error rate|bit error rate]] (BER) is excessively high.

===aptX LL===
''aptX LL'' or ''aptX Low Latency'' is intended for video and gaming applications requiring comfortable audio-video synchronization whenever the stereo audio is transmitted over short-range radio to the listener(s) using the Bluetooth A2DP audio profile standard. The technology offers an end-to-end latency of 32&nbsp;ms over Bluetooth. By comparison, the latency of standard Bluetooth stereo varies greatly depending on the system implementation and buffering. Solutions are available that use standard SBC encoding/decoding that achieve end-to-end latency of less than 40&nbsp;ms. The recommended latency for audio-to-video synchronization in broadcast television is within +40&nbsp;ms and −60&nbsp;ms (audio before/after video, respectively).<ref>{{Cite web|url=https://www.aptx.com/aptx-low-latency|title=Qualcomm aptX Low Latency Synchronised Audio|website=www.aptx.com|access-date=2019-09-22}}</ref> However, AptX Low Latency requires a dedicated, wireless antenna, so it did not achieve much adoption in smartphones and was retired by Qualcomm in favor of aptX Adaptive.<ref name="SoundGuys">{{Cite web|url=https://www.soundguys.com/aptx-adaptive-explained-18768/|title=aptX Adaptive: The new king of Bluetooth?|date=2018-11-30|website=SoundGuys|language=en-US|access-date=2019-09-22}}</ref><ref>{{cite news |title=RTL Live Stream |url=https://helpmag.de/rtl-live-stream/ |access-date=22 June 2023}}</ref> Its main competitor is the [[LHDC (codec)#LLAC|LLAC]].

===aptX HD===
''aptX HD'' or ''aptX High Definition'' has bit-rate of 576 kbit/s. It supports high-definition audio up to 48&nbsp;kHz sampling rates and sample resolutions up to 24 bits.  Unlike the name suggests, the codec is still considered lossy;<ref name="AVHub 2016">{{cite web | title=aptX HD - lossless or lossy? | website=AVHub | date=2016-11-22 | url=http://www.avhub.com.au/news/sound-image/aptx-hd---lossless-or-lossy-442124 | access-date=2018-01-13}}</ref> however, it permits a "hybrid" coding scheme for applications where average or peak compressed data rates must be capped at a constrained level. This involves the dynamic application of "near lossless" coding for those sections of audio where completely lossless coding is impossible due to bandwidth constraints. "Near lossless" coding maintains a high-definition audio quality, retaining audio frequencies up to 20&nbsp;kHz and a dynamic range of at least 120&nbsp;dB. Its main competitors are [[LDAC (codec)|LDAC codec]] developed by Sony and [[LHDC (codec)|LHDC]].

Another scalable parameter within aptX HD is coding latency. It can be dynamically traded against other parameters such as levels of compression and computational complexity. The latency of the aptX HD codec can be scaled to as low as 1 ms for 48&nbsp;kHz sampled audio, depending on the settings of other configurable parameters. aptX HD 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 the benefit of a low computational overhead compared to well-known lossy codecs, such as [[MP3]] and [[Advanced Audio Coding|AAC]]. This is particularly important for deeply embedded audio applications running on low-power mobile devices. aptX HD 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 HD can encode a 48&nbsp;kHz 16-bit stereo audio stream using only 10 MIPS on a modern RISC [[Central processing unit|processor]] with [[Signal processing|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|quality of service]] (QoS) can vary rapidly. Depending on the settings of parameters, decoder resynchronization can occur within 1–2 ms.<ref>{{Cite web|url=https://www.aptx.com/aptx-hd|title=Qualcomm aptX HD Audio|website=www.aptx.com|access-date=2019-09-22}}</ref><ref>{{Cite web|url=https://www.androidauthority.com/aptx-hd-audio-codec-explained-789342/|title=AptX HD - what is it and why should I care?|date=2017-08-30|website=Android Authority|language=en-US|access-date=2019-09-22}}</ref>

===aptX Adaptive===
''aptX Adaptive'' is a next-generation dynamically adjustable audio codec intended for premium audio quality and low-latency. aptX Adaptive's bitrate scales dynamically between 279 kbit/s and 420 kbit/s. It also works with a shared, rather than dedicated, wireless antenna.<ref name="SoundGuys"/> Qualcomm claims their new compression algorithm provides a compression ratio between 5:1 to 10:1. This allows aptX Adaptive at 279 kbit/s and 420 kbit/s to produce the same sound quality as aptX at 352 kbit/s and aptX HD at 576 kbit/s. aptX Adaptive supports 16 and 24 bit-depths at 44.1, 48, and 96&nbsp;kHz sample rates. Actual 96&nbsp;kHz support, however, is depending on actual product hardware implementation. For example, B&O H95 only support 48&nbsp;kHz at max even with AptX Adaptive support. Hardware aptX Adaptive has end-to-end latency of 80 ms,<ref name=aptx-adaptive /> but most phones are using a software transmitter - which does not have any latency advantages over other codecs.<ref>{{Cite web|url=https://www.youtube.com/watch?v=J5PjWMof0FE |archive-url=https://ghostarchive.org/varchive/youtube/20211215/J5PjWMof0FE |archive-date=2021-12-15 |url-status=live|title=aptX Adaptive shocked us! Vivo TWS Neo "review"!|website=[[Company:YouTube|YouTube]] |date=2020-09-10|access-date=2021-04-06}}{{cbignore}}</ref> aptX Adaptive is also backward compatible with older aptX and aptX HD codecs, but not with aptX LL.<ref name="SoundGuys"/><ref>{{Cite web|url=https://www.soundguys.com/aptx-adaptive-explained-18768/|title=Qualcomm aptX Adaptive Audio Codec Technology|website=www.aptx.com|access-date=2019-09-22}}</ref><ref>{{Cite web|url=https://www.qualcomm.com/news/releases/2018/08/31/qualcomms-new-aptx-adaptive-designed-bring-dynamic-next-gen-premium|title=Qualcomm's New aptX Adaptive Designed to Bring Dynamic Next-Gen Premium Wireless Audio Experiences for Gaming, Video and Music|date=2018-08-29|website=Qualcomm|language=en|access-date=2019-09-22}}</ref><ref>{{Cite web|url=https://www.xda-developers.com/qualcomm-aptx-adaptive-bluetooth-audio-codec/|title=AptX Adaptive Bluetooth codec compresses audio at variable bitrate|date=2018-08-31|website=xda-developers|language=en-US|access-date=2019-09-22}}</ref>

====aptX Voice====
''aptX Voice'' is a new feature of aptX Adaptive, and is designed to significantly improve the quality of voice for those using Bluetooth accessories to make voice calls. It does this by delivering 32&nbsp;kHz voice call quality within the Bluetooth Hands-Free Profile.<ref>{{Cite web|url=https://www.qualcomm.com/news/releases/2020/01/06/qualcomm-introduces-aptx-voice-audio-technology-higher-quality-voice-calls|title=Qualcomm Introduces aptX Voice Audio Technology for Higher Quality Voice Calls|date=2020-01-06|website=qualcomm|language=en-US|access-date=2020-03-27}}</ref>

==Mode of operation==
The example CD-quality 16-bit 44&nbsp;kHz (up to 22&nbsp;kHz signal bandwidth) stream is divided by two layers of 64-tap QMF ([[Quadrature mirror filter]]) into four 16-bit subbands of 11&nbsp;kHz (up to 5.5&nbsp;kHz signal bandwidth each). The first 64-tap QMF divides into two bands (0–11&nbsp;kHz and 11–22&nbsp;kHz bands), and then each one is fed into another 64-tap QMF dividing into four bands: 0–5.5&nbsp;kHz, 5.5–11&nbsp;kHz, 11–16.5&nbsp;kHz and 16.5–22&nbsp;kHz. Reduced variance is generally expected to be found in higher bands compared to lower bands, thus ADPCM is employed to allocate bits optimally.

Each band is coded with ADPCM using bit allocation of 8 bits for band 1 (0-5.5&nbsp;kHz spectrum), 4 bits for band 2 (5.5–11&nbsp;kHz), 2 bits each for bands 3 and 4 (11-16.5&nbsp;kHz and 16.5–22&nbsp;kHz). A future modification is considered with adaptive bit reallocation based on variance analysis of each subband, for example 9, 2, 3, 2 etc.

As a result, for mono channel, 16 bits @ 44.1&nbsp;kHz=705.6 kbit/s input is converted into (4×16) 64 bits@11.025&nbsp;kHz=705.6 kbit/s and then to (8+4+2+2) 16 bits @ 11.025&nbsp;kHz=176.4 kbit/s.

Optionally (adds a small delay) a short-term RMSE analyzer is used to reduce dynamic range, and thus allocate bits more effectively during quiet passages (i.e. lossy format).

For a stereo signal, a standard PCM 1.4-Mbit stream is converted into 352 Kbit/sec aptX stream.

Details can be found in the EP0398973B1<ref>{{cite web
| url=https://patents.google.com/patent/EP0398973B1/en
| title=EP0398973B1: Method and apparatus for electrical signal coding
| access-date=2019-01-07}}</ref> patent. The main reasoning is that signal variation is reduced at higher frequencies, which makes it amenable to coding with codecs like ADPCM.

==See also==
* [[List of codecs]]
* [[LDAC (codec)]] (competitor codec)
* [[LHDC (codec)|LHDC]] and [[LHDC (codec)#LLAC|LLAC]] (competitor codec)
* Lossy data compression

==References==
{{Reflist|30em}}

== External links ==
* [https://web.archive.org/web/20160814032046/http://www.radioworld.com/article/article-skips-second-coding-family/18847 Article Skips Second Coding Family], Radio World 09.12.2007
* {{Cite web |url=http://www.entertainmentengineering.com/v6.issue06/EEv6i6.pdf |title=Entertainment Engineering, Volume 6, Issue 6: Licensable Intellectual Property for HD Digital Audio |access-date=June 29, 2009 |archive-url=https://web.archive.org/web/20120216090835/http://www.entertainmentengineering.com/v6.issue06/EEv6i6.pdf |archive-date=February 16, 2012 |url-status=bot: unknown }}

{{Compression formats}}

[[Category:Audio codecs]]

{{Sourceattribution|AptX}}