TheAdaptive Multi-Rate(AMR,AMR-NBorGSM-AMR)audio codecis anaudio compression formatoptimized forspeech coding.AMR is a multi-ratenarrowbandspeechcodecthat encodes narrowband (200–3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbit/s with toll quality[3]speech starting at 7.4 kbit/s.[4]
| Filename extension |
.amr,.3ga |
|---|---|
| Internet media type |
audio/amr, audio/3gpp, audio/3gpp2 |
| Initial release | 23 June 1999[1][2] |
| Latest release | 14.0.0 17 March 2017 |
| Type of format | Lossyaudio |
| Open format? | Yes |
| Free format? | No |
AMR was adopted as the standard speechcodecby3GPPin October 1999 and is now widely used inGSM[5]andUMTS.It useslink adaptationto select from one of eight different bit rates based on link conditions.
AMR is also a file format for storing spoken audio using the AMR codec. Many modern mobile telephone handsets can store short audio recordings in the AMR format, and bothfreeand proprietary programs exist (seeSoftware support) to convert between this and other formats, although AMR is a speech format and is unlikely to give ideal results for other audio. The commonfilename extensionis.amr.There also exists another storage format for AMR that is suitable for applications with more advanced demands on the storage format, like random access or synchronization with video. This format is the 3GPP-specified3GPcontainer formatbased on ISO base media file format.[6]
Usage
editThe frames contain 160 samples and are 20 milliseconds long.[1]AMR uses various techniques, such asACELP,DTX,VADandCNG.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 codingis reduced andchannel codingis 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 afull rate channel (FR)and six on ahalf rate channel (HR).
| Mode | Bitrate (kbit/s) | Channel | Compatible with |
|---|---|---|---|
| AMR_12.20 | 12.20 | FR | ETSI GSM enhanced full rate |
| AMR_10.20 | 10.20 | FR | |
| AMR_7.95 | 7.95 | FR/HR | |
| AMR_7.40 | 7.40 | FR/HR | TIA/EIA IS-641 TDMA enhanced full rate |
| AMR_6.70 | 6.70 | FR/HR | ARIB 6.7 kbit/s enhanced full rate |
| AMR_5.90 | 5.90 | FR/HR | |
| AMR_5.15 | 5.15 | FR/HR | |
| AMR_4.75 | 4.75 | FR/HR | |
| AMR_SID | 1.80 | FR/HR |
Features
edit- 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 utilizesdiscontinuous transmission(DTX), withvoice activity detection(VAD) andcomfort 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 asline spectral pairs(LSP).
- The residual waveform is coded usingalgebraic code-excited linear prediction(ACELP).
- The complexity of the algorithm is rated at 5, using a relative scale whereG.711is 1 andG.729ais 15.
- PSQMtesting under ideal conditions yieldsmean opinion scoresof 4.14 for AMR (12.2 kbit/s), compared to 4.45 forG.711(μ-law)[citation needed]
- PSQM testing under network stress yieldsmean opinion scoresof 3.79 for AMR (12.2 kbit/s), compared to 4.13 forG.711(μ-law)
Licensing and patent issues
editAMR codecs incorporate severalpatentsofNokia,Ericsson,NTTand VoiceAge,[7][8]the last one being theLicense Administratorfor the AMRpatent pools.VoiceAge also accepts submission of patents for determination of their possible essentiality to these standards.[9][10]
The initial fee for professional content creation tools and "real-time channel" products is US$6,500.[when?]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.[7][8]
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.[7][8]
More information:
- VoiceAge licensing information,including pricing to license the AMR codecs
- 3GPP legal issues
- The 3G Patent Platform and its licensing policy
- AMR Codecs as Shared Libraries— legal notices for usage of amrnb and amrwb libraries based on the reference implementation
Software support
edit- 3GPP TS 26.073 – AMR speech Codec (C source code) – reference implementation[11]
- Audacity(beta version 1.3) via the FFmpeg integration libraries[12](both input and output format)
- FFmpegwith OpenCORE AMR libraries[13]
- Android[14]Used for voice recorder.
- AMR Codecs as Shared Libraries– 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:RetroCode,Amr2Wav,both are in an early developmental stage
- AMR Playeris freeware to play AMR audio files, and can convert AMR from/to MP3/WAV audio format.
- Nokia Multimedia Converter 2.0can 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[15])
- Parole Media Player 0.8.1 (in Ubuntu 16.04)
- QuickTimePlayer and multimedia framework
- RealPlayerversion 11 and later
- VLC media playerversion 1.1.0 and later (input format only, not output format)
- ffdshow
- AppleiPhone(can play back AMR files)
- iOS&macOS(iMessage)
- BlackBerrysmartphones (used for voice recorder file format, whileBlackBerry 10cannot play AMR format)
- K-Lite Codec Pack
- Media Player Classic Home Cinema, around 1.7.1
- foobar2000with the componentfoo_input_amr
See also
editReferences
edit- ^ab"3GPP TS 26.090 - Mandatory Speech Codec speech processing functions; Adaptive Multi-Rate (AMR) speech codec; Transcoding functions".3GPP.Retrieved2010-07-21.
- ^"3GPP TS 26.071 - Mandatory speech CODEC speech processing functions; AMR speech Codec; General description".3GPP.Retrieved2010-07-21.
- ^"What's toll-quality voice?".ITworld.13 December 2000.Retrieved26 July2019.
- ^RFC 4867 - RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio CodecsPage 35
- ^"Sorting Through GSM Codecs: A Tutorial".11 July 2003.
- ^RFC 4867 - RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio CodecsPage 35
- ^abcVoiceAge Corporation (2007-10-14)."AMR Licensing Terms".VoiceAge Corporation. Archived fromthe originalon 2007-10-14.Retrieved2009-09-12.
- ^abcVoiceAge Corporation (June 2007)."AMR Licensing Terms".VoiceAge Corporation. Archived fromthe originalon 2007-10-14.Retrieved2009-09-12.
- ^VoiceAge Corporation."Licensing - Patent Calls".VoiceAge Corporation. Archived fromthe originalon 2007-10-14.Retrieved2009-09-12.
- ^VoiceAge Corporation (2007-10-14)."Licensing - Patent Calls".Archived fromthe originalon 2007-10-14.Retrieved2009-09-12.
- ^3GPP (2008-12-11)3GPP TS 26.073 - AMR speech Codec,Retrieved 2009-09-08
- ^Retrieved on 2010-02-28
- ^FFmpeg General Documentation - AMR external library,Retrieved on 2009-07-08
- ^Android AMR codecs,Retrieved on 2009-07-08ArchivedFebruary 18, 2009, at theWayback Machine
- ^KMPlayer Internal Audio Decoder PreferencesArchived2014-10-22 at theWayback Machine,Retrieved 2014-10-22
External links
edit- 3GPP TS 26.090 – Mandatory Speech Codec speech processing functions; Adaptive Multi-Rate (AMR) speech codec; Transcoding functions
- 3GPP TS 26.071 – Mandatory Speech Codec speech processing functions; AMR Speech Codec; General Description
- 3GPP codecs specifications; 3G and beyond / GSM, 26 series
- RFC4867– RTP Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codecs
- RFC4281– The Codecs Parameter for "Bucket" Media Types