adaptive Multi-Rate audio codec

The frames contain 160 samples and are 20 milliseconds long. AMR uses various techniques, such as ACELP, DTX, VAD and CNG. The usage of AMR requires optimized link adaptation that selects the best codec mode to meet the local radio channel and capacity requirements. If the radio conditions are bad, source coding is reduced and channel coding is increased. This improves the quality and robustness of the network connection while sacrificing some voice clarity. In the particular case of AMR this improvement is somewhere around S/N = 4–6 dB for usable communication. The new intelligent system allows the network operator to prioritize capacity or quality per base station.

There are a total of 14 modes of the AMR codec, eight are available in a full rate channel (FR) and six on a half rate channel (HR).

• Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz.
• The AMR codec uses eight source codecs with bit-rates of 12.2, 10.2, 7.95, 7.40, 6.70, 5.90, 5.15 and 4.75 kbit/s.
• Generates frame length of 95, 103, 118, 134, 148, 159, 204, or 244 bits for AMR FR bit rates 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, or 12.2 kbit/s, respectively. AMR HR frame lengths are different.
• AMR utilizes discontinuous transmission (DTX), with voice activity detection (VAD) and comfort noise generation (CNG) to reduce bandwidth usage during silence periods
• Algorithmic delay is 20 ms per frame. For bit-rates of 12.2, there is no "algorithm" look-ahead delay. For other rates, look-ahead delay is 5 ms. Note that there is 5 ms "dummy" look-ahead delay, to allow seamless frame-wise mode switching with the rest of rates.
• AMR is a hybrid speech coder, and as such transmits both speech parameters and a waveform signal
• Linear predictive coding (LPC) is used to synthesize the speech from a residual waveform. The LPC parameters are encoded as line spectral pairs (LSP).
• The residual waveform is coded using algebraic code-excited linear prediction (ACELP).
• The complexity of the algorithm is rated at 5, using a relative scale where G.711 is 1 and G.729a is 15.
• PSQM testing under ideal conditions yields mean opinion scores of 4.14 for AMR (12.2 kbit/s), compared to 4.45 for G.711 (μ-law){{citation needed|date=October 2019}}
• PSQM testing under network stress yields mean opinion scores of 3.79 for AMR (12.2 kbit/s), compared to 4.13 for G.711 (μ-law)

AMR codecs incorporate several patents of Nokia, Ericsson, NTT and VoiceAge,{{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}}{{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 }} the last one being the License Administrator for the AMR patent pools. VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards.{{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 }}{{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}}

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.

In the category of personal computer products, e.g., media players, the AMR decoder is licensed for free. The license fee for a sold encoder falls from $0.40 to $0.30 with volume, up to a maximum of $300,000 annually. The minimum annual royalty is not applied to licensed products that fall under the category of personal computer products and use only the free decoder.

More information:

• [http://www.voiceage.com/licensing.php VoiceAge licensing information], including pricing to license the AMR codecs
• [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] — legal notices for usage of amrnb and amrwb libraries based on the reference implementation

• 3GPP TS 26.073{{snd}}AMR speech Codec (C source code){{snd}}reference implementation3GPP (2008-12-11) [http://www.3gpp.org/ftp/Specs/archive/26_series/26.073/26073-800.zip 3GPP TS 26.073 - AMR speech Codec], Retrieved 2009-09-08
• Audacity (beta version 1.3) via the FFmpeg integration librariesRetrieved on 2010-02-28 (both input and output format)
• FFmpeg with OpenCORE AMR libraries[http://www.ffmpeg.org/general.html FFmpeg General Documentation - AMR external library], Retrieved on 2009-07-08
• Android[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 }} Used for voice recorder.
• [http://www.penguin.cz/~utx/amr AMR Codecs as Shared Libraries]{{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: [http://sourceforge.net/projects/retrocode/ RetroCode], [http://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.
• MPlayer (SMPlayer, KMPlayer[http://www.softadept.com/read/kmplayer-internal-audio-decoder-preferences-overview/ KMPlayer Internal Audio Decoder Preferences] {{webarchive|url=https://web.archive.org/web/20141022231354/http://www.softadept.com/read/kmplayer-internal-audio-decoder-preferences-overview/ |date=2014-10-22 }}, Retrieved 2014-10-22)
• Parole Media Player 0.8.1 (in Ubuntu 16.04)
• QuickTime Player and multimedia framework
• RealPlayer version 11 and later
• VLC media player version 1.1.0 and later (input format only, not output format)
• ffdshow
• Apple iPhone (can play back AMR files)
• iOS & macOS (iMessage)
• BlackBerry smartphones (used for voice recorder file format, while BlackBerry 10 cannot play AMR format)
• K-Lite Codec Pack
• Media Player Classic Home Cinema, around 1.7.1
• foobar2000 with the component [https://github.com/unjello/foo_input_amr/ foo_input_amr]

• Adaptive Multi-Rate Wideband (AMR-WB)
• Extended Adaptive Multi-Rate – Wideband (AMR-WB+)
• Half Rate
• Full Rate
• Enhanced Full Rate (EFR)
• Sampling rate
• IS-641
• 3GP
• Comparison of audio coding formats
• RTP audio video profile

{{reflist|30em}}

• [http://www.3gpp.org/ftp/Specs/html-info/26090.htm 3GPP TS 26.090{{snd}}Mandatory Speech Codec speech processing functions; Adaptive Multi-Rate (AMR) speech codec; Transcoding functions]
• [http://www.3gpp.org/ftp/Specs/html-info/26071.htm 3GPP TS 26.071{{snd}}Mandatory Speech Codec speech processing functions; AMR Speech Codec; General Description]
• [http://www.3gpp.org/ftp/Specs/html-info/26-series.htm 3GPP codecs specifications; 3G and beyond / GSM, 26 series]
• {{IETF RFC|4867|link=no}}{{snd}}RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs
• {{IETF RFC|4281|link=no}}{{snd}}The Codecs Parameter for "Bucket" Media Types

{{Compression formats}}

Category:Speech codecs

Category:1999 software