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.
Topics on this page
Technical Background
Technical Highlights
AMR-WB+ at a Glance
Benefits
Applications
AMR-WB+ Standard Specifications
File Format and RTP Packet Format Definitions
Technical Reports for Download
Now a breakthrough compression technology — 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.
The 3GPP-standard AMR-WB+ audio codec extends the AMR-WB wideband speech codec standard by combining unrivaled ACELP® speech coding technology with advanced audio coding technology, thereby enabling service providers to deliver consistent high-quality audio while making efficient use of their transmission capacity.
In addition to delivering the same rich, natural-sounding wideband speech as AMR-WB, 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 such as multimedia streaming, mobile TV/radio broadcasts, podcasting, 3GPP Packet-switched Streaming Service (PSS), Multimedia Messaging Services (MMS), Multimedia Broadcast/Multimedia Service (MBMS), IP Multimedia Subsystem (IMS) Messaging Service and Presence Service and other applications.
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Technical Background
Selected as an audio codec standard in February 2004 by ETSI/3GPP, AMR-WB+ utilizes a hybrid of two technologies: ACELP® and TCX, respectively Algebraic Code Excited Linear Prediction® and Transform Coded Excitation. ACELP® technology is in more than 15 international telecommunications standards, including AMR narrowband, AMR-WB, ITU-T G.729 and ITU-T G.723.1 at 5.3 kbps.
The AMR-WB+ codec operates across a wide range of bit rates, from 6 to 36 kbps for mono signals and 7 to 48 kbps for stereo.
In the 3GPP standardization tests for audio codecs, AMR-WB+ performed better than the other codec for all content types at low bit rates (up to 20 kbps). At 20 kbps in stereo mode, AMR-WB+ is equivalent when music, speech and mixed content are averaged, and performs better for both speech and mixed content. In mono mode, AMR-WB+'s quality at 15.25 kbps is equivalent to the other codec's at 20 kbps, and its quality at 9.75 kbps is equivalent to the other codec's at 16 kbps. AMR-WB+ therefore provides bandwidth efficiencies of 25% to 40% to deliver equivalent quality.
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Technical Highlights
The AMR-WB+ codec is characterized by these important features:
Hybrid ACELP®/TCX codec provides consistent performance across both speech and audio content types, including music, speech-between-music and speech-over-music
High-efficiency parametric stereo (HE-PS) provides high-fidelity stereo image reproduction at lowest bit rates
Coding modes can be adapted according to network congestion and desired quality of service (QoS). High scalability from
– 6-36 kbps for mono
– 7-48 kbps for stereo
Low decoder complexity for PSS/MMS decoder, resulting in low power consumption:
– Less than 13 WMOPS for mono
– Less than 24 WMOPS for stereo
– MMS encoder complexity comparable to AMR-WB codec
Small incremental increase in footprint compared to AMR-WB codec
Backward compatibility with AMR-WB, the mandatory codec for wideband speech in the 3GPP Release 5 (and up) specifications (standardized in 3GPP and ITU-T)
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AMR-WB+ at a Glance
Selection date February 2004 by 3GPP (standard approved September 2004)
Bits rate
(Kbps) Mono: 6-36 kbps
Stereo: 7-48 kbps
Type ACELP®/TCX
Encoded bandwidth Ranges from 50 Hz - 7.2 kHz up to 50 Hz - 19.2 kHz
Delay (ms):
Frame size
Lookahead
80
40
Quality For speech, performance better than or equal to AMR-WB.
For music performance better than or equal to AAC Plus in most tests, and at low bit rate (less than 18 kbps) audio performance better than AAC Plus.
Complexity (WMOPS)
RAM + ROM
(Kwords)
PROM
(Kwords)
Decoder
Mono 13
Stereo 24
Mono 22.6
Stereo 27.3
Mono 4.0
Stereo 4.9
MMS encoder
Stereo 36
Stereo 36.1
Stereo 6.8
PSS encoder
Stereo 62
Stereo 40
Stereo 6.8
Fixed-point
Bit-exact C available for encoder and decoder
Floating-point C-code available for encoder and decoder
Principal
applications
PSS, MMS, MBMS, IMS Messaging Service and Presence Service
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Benefits
To secure broad-based acceptance of 3GPP multimedia services, service providers must meet subscribers’ expectations of high-quality audio at a fair price. AMR-WB+ provides the best quality in mobile environments for mixed content: speech and audio (music and other audio). The 3GPP PSS/MMS selection exercise for low-bit-rate audio codecs demonstrated that AMR-WB+ provides equal or better performance, for any content, than any codec available in the 3GPP Release 5 specifications. And for PSS applications, the music quality is better than or equal to that provided by MPEG-4 AAC Plus in most tests.
An additional benefit to subscribers, and therefore to service providers, is AMR-WB+'s low decoder complexity, which is directly related to implementability on low-cost mass market devices. Its low complexity helps ensure real-time performance on low- to mid-tier processors, ensuring the delivery of high-quality multimedia services problem free across a wide set of end-user devices and so greatly increasing the addressable market of users who can benefit from these services. Moreover, its more efficient use of internal and network resources leaves more resources for application processing, big color screens, speakers and other power-hungry features as it helps increase battery-charge operating time of the mobile handset.
To deliver services at a fair price, service providers must operate at the lowest possible cost, making efficient use of bandwidth. Low bit rate transmission is particularly important for MMS services, in which message sizes are limited. At the commercially relevant low bit rates of 14 kbps for mono and 18 kbps for stereo, AMR-WB+ clearly satisfies this requirement.
To ensure the quality and cost-efficiency of AMR-WB+ implementations, the AMR-WB+ codec is offered with open specifications for decoder and encoder. As well, source code both in floating-point and fixed-point arithmetic is available. And in order to facilitate fast time-to-market, favorable licensing terms have already been established. Details can be found here.
When providers of streaming and multimedia messaging services consider the need to balance the consistent quality of the signal against deployment costs, it’s clear that AMR-WB+ is certain to create more revenue for the mobile industry than any other codec of its type.
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Applications
Mobile TV/radio streaming, broadcast and podcast
▪ Talk shows, news, traffic, weather ▪ Sports events/highlights ▪ Entertainment ▪ Movies & trailers ▪ Animation & cartoons ▪ Audio books ▪ Music videos
Server-Based Streaming (PSS)
▪ Music and other audio content in mono and stereo ▪ Movies ▪ Video clips ▪ News programming ▪ Sports events ▪ Audio books ▪ Commercial advertisements ▪ Access to multimedia information systems ▪ Interactive gaming ▪ “Infotainment”
Multimedia Messaging Services (MMS)
▪ Person-to-person messaging ▪ Application-to-person messaging ▪ Instant messaging
Multimedia Broadcast/Multicast Service (MBMS)
▪ Live TV ▪ Radio programming ▪ Multi-player interactive gaming ▪ Commercial advertisements
IP Multimedia Subsystem (IMS) Messaging Service and Presence Service
▪ Immediate messaging ▪ Session-based messaging
Download Services
▪ Hi-fi ringtones ▪ Music ▪ Video clips ▪ Movie trailers ▪ Audio books
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AMR-WB+ Standard Specifications
The AMR-WB+ audio codec is specified for 3GPP multimedia applications and DVB-H mobile TV. It is defined, described and recommended in these standards:
3GPP 2004 TS 26.290 describes the codec and refers to related specifications.
http://www.3gpp.org/ftp/Specs/html-info/26290.htm
3GPP 2005 TS 26.140 recommends that if MMS supports audio, it should support AMR-WB+. http://www.3gpp.org/ftp/Specs/html-info/26140.htm
3GPP 2006 TS 26.141 recommends that if IP Multimedia Subsystem (IMS) Messaging and Presence support audio, they should support AMR-WB+.
http://www.3gpp.org/ftp/Specs/html-info/26141.htm
3GPP 2005 TS 26.234 recommends that if packet-switched streaming (PSS) supports audio, it should support AMR-WB+. http://www.3gpp.org/ftp/Specs/html-info/26234.htm
3GPP (2005) TS 26.346 states that Multimedia Broadcast/Multicast Service (MBMS) clients that support audio should support the AMR-WB+ decoder.
http://www.3gpp.org/ftp/Specs/html-info/26346.htm
ETSI TS 102 005 V1.2.1 (2006-04), "Digital Video Broadcasting (DVB); Specification for the use of Video and Audio Coding in DVB services delivered directly over IP protocols," specifies AMR-WB+ for use in DVB services delivered over Internet Protocol and IP Datacast. http://www.dvb-h.org/technology.htm
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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, AMR-WB, VMR-WB and AMR-WB+ 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 3GPP multimedia services such as 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 (2006) RFC 4352, “RTP Payload Format for Extended AMR Wideband (AMR-WB+) Audio Codec,” specifies an RTP payload format for Extended AMR Wideband (AMR-WB+) encoded audio signals. The AMR-WB+ codec is an audio extension of the AMR-WB speech codec. It encompasses the AMR-WB frame types and a number of new frame types designed to support high quality music and speech. A media type registration for AMR-WB+ is included. http://www.ietf.org/rfc/rfc4352.txt?number=4352
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Technical Reports for Download
These reports show why AMR-WB+ is ideal for mobile multimedia and broadcast applications. Please download one or more of them for detailed technical information on AMR-WB+.
In Extended AMR-WB for High-Quality Audio on Mobile Devices, the authors review the requirements for an audio codec for mobile multimedia applications and then present the architecture and functioning of the AMR-WB+ audio codec. They also present performance testing results and conclude that AMR-WB+ is able to consistently deliver high-quality audio for all content types, even at very low bit rates. By Redwan Salami, Roch Lefebvre, Ari Lakaniemi, Kalervo Kontola, Stephan Bruhn and Anisse Taleb. Published in IEEE Transactions on Communications, Vol. 44, No. 5, May 2006.
3GPP Release 6 Codecs for Audio-Visual Broadcast Service by Stefan Bruhn, Per Frojdh, Thorsten Lohmar, Anisse Taleb. Presented at IEEE Symposium on Broadband Multimedia Systems and Broadcasting 2006.
Two audio codecs were chosen for mobile multimedia applications in 3GPP Release 6. The authors assess their performance using combined listening and viewing tests in various usage scenarios and conclude that, unlike the other codec, AMR-WB+ performs consistently across diverse content types, including music, speech and mixed content, and provides higher quality at low and even very low bit rates.
AMR-WB+: Low Bit Rate Audio Coding for Mobile Multimedia by Kalervo Kontola, Jari M. Makinen, Anisse Taleb, Stephan Bruhn, Bruno Bessette, Redwan Salami. Presented at IEEE Symposium on Broadband Multimedia Systems and Broadcasting 2006.
This article looks at the audio component of mobile multimedia applications, explains its requirements and constraints and then explains why AMR-WB+ is the best codec for mobile multimedia broadcasting, streaming and podcasting applications.
Report On Perceptual Tests of Coders at Low- and Very Low-Bit Rates by Ellyn G. Sheffield, PhD, describes a two-phase study carried out for U.S. National Public Radio that evaluated digital codecs at low and very low bit rates (11.9-24 kbps and 0-11.8 kbps, respectively) for speech, voiceover, rock, jazz and classical music.
In the selection phase, experts ranked AMR-WB+ in the top 2 in a field of 9 competitors at low bit rates and scored it more than 20 percent higher than the nearest competitor (in a field of 10) in the very low bit rate category.
In the consumer test phase, participants rated AMR-WB+ as outperforming the other codecs and being equivalent to the source reference for speech at low bit rates. They also rated AMR-WB+ as superior to current low-bandwidth transmissions for music. At very low bit rates, AMR-WB+ performed best, even better than existing transmissions, especially in speech. Moreover, listeners did not tire of listening to AMR-WB+ recordings when longer samples were played, claiming they were satisfied with the quality.
The full report is available at: http://www.euonline.org/pub/iboc/low_bit_rate_coder_report.pdf