Adaptive Multi-Rate audio codec: Difference between revisions

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{{Short description|Audio compression format optimized for speech coding}}

{{Cleanup bare URLs|date=August 2022}}

{{Infobox file format

| name = Adaptive Multi-Rate (AMR)

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}}

The '''Adaptive Multi-Rate''' ('''AMR''', '''AMR-NB''' or '''GSM-AMR''') '''audio codec''' is an [[audio compression format]] optimized for [[speech coding]]. AMR speech codec consists ofis a multi-rate [[narrowband]] speech [[codec]] that encodes narrowband (200–3400&nbsp;Hz) signals at variable bit rates ranging from 4.75 to 12.2&nbsp;kbit/s with toll quality<ref>{{cite web |title=What's toll-quality voice? |url=https://www.itworld.com/article/2783105/what-s-toll-quality-voice-.html |website=ITworld |date=13 December 2000 |access-date=26 July 2019}}</ref> speech starting at 7.4&nbsp;kbit/s.<ref>[http://tools.ietf.org/html/rfc4867#page-5 RFC 4867 - RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs] Page 35</ref>

AMR was adopted as the standard speech [[codec]] by [[3GPP]] in October 1999 and is now widely used in [[GSM]]<ref>{{cite web | url=http://www.eetimes.com/electronics-news/4139026/Sorting-Through-GSM-Codecs-A-Tutorial | title=Sorting Through GSM Codecs: A Tutorial | date=11 July 2003 }}</ref> and [[UMTS]]. It uses [[link adaptation]] to select from one of eight different bit rates based on link conditions.

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== Licensing and patent issues ==

AMR codecs incorporate several [[patent]]s of [[Nokia]], [[Ericsson]], [[Nippon Telegraph and Telephone|NTT]] and VoiceAge,<ref name="voiceage-amr_licterms">{{cite web |author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/amr_licterms.php |title=AMR Licensing Terms |date=2007-10-14 |access-date=2009-09-12 |archive-url=https://web.archive.org/web/20071014162046/http://www.voiceage.com/amr_licterms.php |archive-date=2007-10-14}}</ref><ref name="voiceage-amr_licterms2">{{cite web|author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/amr_licterms.php |title=AMR Licensing Terms |date=June 2007 |access-date=2009-09-12 |url-status=dead |archive-url=https://web.archive.org/web/20071014162046/http://www.voiceage.com/amr_licterms.php |archive-date=2007-10-14 }}</ref> the last one being the ''License Administrator'' for the AMR [[patent pool]]s. VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards. However, it's very difficult to determine if there were actually any patents in existence for the so-called inventions related to AMR/AMR-WB codecs, since inventors (and their lawyers) do everything they can to hide patents related to AMR/AMR-WB technology{{Citation needed|date=February 2016}}. Apparently, all these patents are hidden from all other researches and general audience that could perhaps spot prior art in the claimed "inventions" patented by the patent holders of the AMR/AMR-WB codecs.<ref name="voiceage-licpatentcalls">{{cite web|author=VoiceAge Corporation |publisher=VoiceAge Corporation |url=http://www.voiceage.com/licpatentcalls.php |title=Licensing - Patent Calls |access-date=2009-09-12 |url-status=dead |archive-url=https://web.archive.org/web/20071014161420/http://www.voiceage.com/licpatentcalls.php |archive-date=2007-10-14 }}</ref><ref name="archive-licpatentcalls">{{cite web |author=VoiceAge Corporation |url=http://www.voiceage.com/licpatentcalls.php |title=Licensing - Patent Calls |date=2007-10-14 |access-date=2009-09-12 |archive-url = https://web.archive.org/web/20071014161420/http://www.voiceage.com/licpatentcalls.php |archive-date = 2007-10-14}}</ref>

The initial fee for professional content creation tools and "real-time channel" products is US$6,500.{{When|date=November 2015}} The minimum annual royalty is $10,000, which, in the first year, excludes the initial fee. Per-channel license fees fall from $0.99 to $0.50 with volume, up to a maximum of $2 million annually.<ref name="voiceage-amr_licterms"/><ref name="voiceage-amr_licterms2"/>

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* [https://web.archive.org/web/20070630180010/http://www.3gpp.org/legal/legal.htm 3GPP legal issues]

* [https://web.archive.org/web/20070630180057/http://www.3gpp.org/faq/faq_2005_2.htm#A3.1 The 3G Patent Platform and its licensing policy]

* [http://www.penguin.cz/~utx/amr AMR Codecs as Shared Libraries] {{Webarchive|url=https://web.archive.org/web/20210411005805/http://www.penguin.cz/~utx/amr |date=2021-04-11 }} — legal notices for usage of amrnb and amrwb libraries based on the reference implementation

== Software support ==

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* [[FFmpeg]] with OpenCORE AMR libraries<ref name="ffmpeg-amr">[http://www.ffmpeg.org/general.html FFmpeg General Documentation - AMR external library], Retrieved on 2009-07-08</ref>

* [[Android (operating system)|Android]]<ref name="android-amr">[http://android.git.kernel.org/?p=platform/external/opencore.git;a=tree;f=codecs_v2/audio/gsm_amr;hb=HEAD Android AMR codecs], Retrieved on 2009-07-08 {{webarchive|url=https://web.archive.org/web/20090218232855/http://android.git.kernel.org/?p=platform%2Fexternal%2Fopencore.git%3Ba%3Dtree%3Bf%3Dcodecs_v2%2Faudio%2Fgsm_amr%3Bhb%3DHEAD |date=February 18, 2009 }}</ref> Used for voice recorder.

* [http://www.penguin.cz/~utx/amr AMR Codecs as Shared Libraries] {{Webarchive|url=https://web.archive.org/web/20210411005805/http://www.penguin.cz/~utx/amr |date=2021-04-11 }}{{snd}}amrnb and amrwb libraries development site. These libraries are based on the reference implementation and were created to prevent embedding of possibly patented source code into many open source projects.

* Open source software to convert the .amr format: [httphttps://sourceforge.net/projects/retrocode/ RetroCode], [httphttps://sourceforge.net/projects/amr2wav/ Amr2Wav], both are in an early developmental stage

* [http://www.amrplayer.com/ AMR Player] is freeware to play AMR audio files, and can convert AMR from/to MP3/WAV audio format.

* [https://web.archive.org/web/20120422173730/http://www.developer.nokia.com/info/sw.nokia.com/id/d1c17a7f-1231-4385-8c17-04f28f4f2d8e/Nokia_Multimedia_Converter_2.0.html Nokia Multimedia Converter 2.0 ] can convert (create) samples, one can use Nokia's conversion tool to create both .amr and .awb files. It works in Windows 7 as well if the setup is run in XP compatibility mode.