Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | AMR-WB+, Extended Adaptive Multi-Rate - Wideband Speech Codec |
| Description | Audio data compression scheme optimized for speech coding in GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System). It is an extension of AMR-WB, adding support for stereo signals, higher sampling rates, and transform coded excitation (TCX) in addition to the Algebraic Code Excited Linear Prediction (ACELP) compression coding featured in AMR and AMR-WB. Automatic switching between TCX and ACELP provides good quality for all types of sound at moderate bit rates. AMR-WB+ is backward compatibile with AMR-WB. The 3GPP (3d Generation Partnership Project) developed the AMR-WB+ audio codec for streaming and messaging services; its primary target applications are Packet-Switched Streaming service (PSS), Multimedia Messaging Service (MMS), and Multimedia Broadcast and Multicast Service (MBMS). (Preceding adapted from the Wikipedia AMR-WB+ entry.) AMR-WB+ is less constrained than AMR-WB; for this reason AMR-WB is treated as a subtype of AMR-WB+ at this Web site; Comments welcome. |
| Production phase | Final-state for end-user delivery. |
| Relationship to other formats | |
| Subtype of | AMR, Adaptive Multi-Rate Speech Codec |
| Has subtype | AMR-WB, Adaptive Multi-Rate - Wideband Speech Codec |
| Used by | DTB_Ext, DTB (Digital Talking Book), Extension for AMR-WB+ Speech Codec |
| LC experience or existing holdings | AMR-WB+ has been selected as the audio codec for LC-produced Digital Talking Books; see also DTB_Ext. |
| LC preference | None |
| Disclosure | Open standard. Developed by 3GPP, a collaboration of telecommunications industry and standards groups in Europe, Asia, and North America. The key European organization is ETSI (European Telecommunications Standards Institute). |
| Documentation | 3GPP TS 26.290 v.6.3.0 (2005-06), 3rd Generation Partnership Project; Technical Specification Group Service and System Aspects; Audio codec processing functions; Extended Adaptive Multi-Rate - Wideband (AMR-WB+) codec; Transcoding functions, and other specifications listed in Format specifications below. Some of the other specifications carry different version numbers; it is not clear to the compiler of this Web page if AMR-WB+ in and of itself has a version number; Comments welcome. Significant technical information about AMR-WB+ is provided by IETF (Internet Engineering Task Force) RFC 4352. |
| Adoption | Not investigated for this page. |
| Licensing and patent claims | A number of patents pertaining to AMR-WB+ are listed at the ETSI Web site. These have not been evaluated by compiler of this Web page. The 3GPP specification for AMR-WB+ states that "pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced [at the ETSI Web server]." |
| Transparency | Depends upon algorithms and tools to read; will require sophistication to build tools. |
| Self-documentation | Technical codes are included that characterize each of the frames that comprise the AMR-WB+ data stream. In addition to the specification, information is provided in IETF RFC 4352. |
| External dependencies | Not investigated for this page. |
| Technical protection considerations | Not investigated for this page. |
| Normal rendering for sound | Not investigated for this page. |
| Fidelity (support for high audio resolution) | Automatic switching between TCX and ACELP provides good quality for all types of sound at moderate bit rates. AMR-WB+ supports various internal sampling frequencies from 12.8 kHz to 38.4 kHz and bit rates from 5.2-48 kbps. Mono rates are scalable from 5.2-36 kbps, and stereo rates are scalable from 6.2-48 kbps, reproducing bandwidth up to 20 kHz (approaching CD quality). |
| Sound field (support for multi-channel audio) | Supports stereo. |
| Functionality beyond normal sound rendering | Not investigated for this page. |
| Tag type | Value | Note |
| Filename Extension | See AMR; Comments welcome | |
| Internet Media Type | audio/AMR-WB+ | From RFC 4352 |
| Magic numbers | See AMR; Comments welcome |
| General | From section 4.3 of the specification: "Principles of the extended adaptive multi-rate wideband codec. The AMR-WB+ audio codec contains all the AMR-WB speech codec modes 1-9 and AMR-WB VAD and DTX. AMRWB+ extends the AMR-WB codec by adding TCX, bandwidth extension, and stereo. The AMR-WB+ audio codec processes input frames equal to 2048 samples at an internal sampling frequency Fs . The internal sampling frequency is limited to the range 12800-38400 Hz, see section 8 for more details. The 2048-sample frames are split into two critically sampled equal frequency bands. This results in two superframes of a 1024 samples corresponding to the low frequency (LF) and high frequency (HF) band. Each superframe is divided into four 256-samples frames. Sampling at the internal sampling rate is obtained by using a variable sampling conversion scheme, which re-samples the input signal. The LF and HF signals are then encoded using two different approaches: the LF is encoded and decoded using the "core" encoder/decoder, based on switched ACELP and transform coded excitation (TCX). In ACELP mode, the standard AMR-WB codec is used. The HF signal is encoded with relatively few bits (16 bits/frame) using a bandwidth extension (BWE) method. The basic set of rates are built based on AMR-WB rates in addition to bandwidth extension. . . . "ACELP encoding and decoding are similar to standard AMR-WB speech codec. The ACELP coding consists of LTP analysis and synthesis and algebraic codebook excitation. The ACELP coding mode is used in AMR-WB operation within AMR-WB+ codec. In TCX mode the perceptually weighted signal is processed in the transform domain. The Fourier transformed weighted signal is quantised using split multi-rate lattice quantisation (algebraic VQ). Transform is calculated in 1024, 512 or 256 samples windows. The excitation signal is recovered by inverse filtering the quantised weighted signal through the inverse weighting filter (same weighting filter as in AMR-WB)." From the VoiceAge AMR-WB+ Web page (consulted April 4, 2007): "Emerging end-to-end digital communication systems enable the use of wideband audio coding in a large and varied collection of applications for mobile environments, including mobile TV/radio, streaming services for music, news and sports and multimedia messaging for person-to-person and business-to-person communications. . . . Extended Adaptive Multi-Rate Wideband (AMR-WB+) addresses mixed speech and audio content, providing superior-quality sound across all content types, even at low and very low bit rates. . . . AMR-WB+ delivers high-quality music, speech-over-music, and speech-between-music, making it perfectly suited to low-bit-rate mixed-content audio applications . . . ." |
| History | From the VoiceAge AMR-WB+ Web page (consulted April 4, 2007): Selected as an audio codec standard in February 2004 by ETSI/3GPP; standard approved September 2004. |
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