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AMR
— The Ultimate Narrowband
Voice Compression Standard
The proven, highly efficient and very robust AMR (Adaptive Multi-Rate) narrowband codec is the 3GPP mandatory standard codec for narrowband speech and multimedia messaging services over 2.5G/3G wireless systems based on evolved GSM core networks (WCDMA, EDGE, GPRS). |
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Initially developed for the GSM system, the single most deployed 2G mobile telecommunication system worldwide, AMR was also standardized by the European Telecommunications Standards Institute (ETSI) in 1999, and in 2006, it was included in the CableLabs® PacketCable™ 2.0 specification.
AMR operating at various bit rates is built into every GSM and WCDMA phone, ensuring that content generated by AMR can be played by virtually any wireless phone in the world
– including hundreds of millions of new phones every year.
Technical Highlights
AMR operates on narrowband (200-3400 Hz) signals at variable bit rates in the range of 4.75 to 12.2 kbps. It provides toll quality speech starting at 7.4 kbps, with near-toll quality and better robustness at lower rates and better reproduction of non-speech sounds at higher rates.
- AMR is the only narrowband speech codec offering eight different bit rates that can be adapted according to network congestion, thus enabling significant enhancement of QoS
- Voice Activity Detector (VAD) functionality included
- Comfort Noise Generation (CNG) included
- Discontinuous Transmission (DTX) functionality included
- In rigorous comparative testing in the selection and characterization phases of the ETSI and 3GPP standardization process, AMR outperformed all competitors and exceeded all requirements for robustness to packet loss, bit errors, and background noise, also demonstrating consistent performance across multiple languages, including English (US and UK), French, German, Italian, Mandarin, and Spanish
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Benefits
AMR narrowband is several steps ahead of its direct speech compression competitors:
- This standard is the only narrowband technology offering such a complete range of built-in features. In most other cases VAD, CNG, or the different bit rates are optional. AMR narrowband provides end-to-end solutions to various applications. The package comprises not only the codec but also VAD, CNG, DTX, payload and storage formats, and hooks to media file formats.
- For VoIP, the eight available bit rates open the door to a striking QoS improvement. AMR flexibility enables the development of applications that control the bit rate according to the network characteristics.
- Coded AMR media can be encapsulated in the 3GP or MPEG-4 file formats and used along the entire delivery chain in multimedia applications.
- AMR is a proven technology that can be applied anywhere low bit rate speech coding is important, for example, in toys.
Without doubt, this technology is paving the way to network convergence — and it will be integrated into millions of applications, as its predecessors were. By implementing AMR narrowband today, companies are gaining a competitive edge, as they are building on a technology that is guaranteed to be around for some time.
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Applications
- Multimedia services for 3G mobile communication systems
- Voice over IP
- Wi-Fi telephony
- Conferencing
- Portable audio devices
- Unified Messaging
- Internet applications
- Digital radio broadcasting
- Streaming
- Content creation tools and content downloads
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Related Standards
The AMR narrowband speech codec is defined, described, recommended and prescribed in these standards:
File Format and RTP Packet Format Definitions
These specifications define the .3gp file format for use in packet-switched streaming services like MMS and PSS and the Real-Time Protocol (RTP) payload formats for packetizing AMR encoded audio signals into the RTP. The RTP payload format definitions enable use of the codecs in RTP packet-switched networks in applications like streaming, and they enable interoperability with existing codec transport formats on non-IP networks.
- 3GPP (2005) RFC 26.244, “Transparent end-to-end packet switched streaming service (PSS); 3GPP file format (3GP),” defines the 3GPP (.3gp) file format used by PSS and MMS and explains how AMR, AMR-WB and AMR-WB+ audio information can be encapsulated in .3gp files.
http://www.3gpp.org/ftp/Specs/html-info/26244.htm
- IETF (2002) RFC 3267, “Real-Time Transport Protocol (RTP) Payload Format and File Storage Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR-WB) Audio Codec,” specifies the payload format for packetizing AMR and AMR-WB encoded speech signals into the RTP. The payload format is designed to enable using the codec in RTP packet-switched networks in applications like VoIP and streaming, and it enables interoperability with existing AMR and AMR-WB transport formats on non-IP networks. In addition, a file format is specified for transport of AMR and AMR-WB speech data in storage mode applications such as email. Two separate MIME type registrations are included, one for AMR and one for AMR-WB, specifying use of both the RTP payload format and the storage format.
http://www.ietf.org/rfc/rfc3267.txt
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