The Best of Both Worlds:
Wideband Speech Plus High-Quality Audio
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.
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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
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| 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:
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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+.
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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.
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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.
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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.
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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
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