Spectral band replication (SBR) is a technology to enhance audio or
speech codecs, especially at low
bit rate
In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time.
The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...
s and is based on harmonic redundancy in the frequency domain.
It can be combined with any
audio compression codec: the codec itself transmits the lower and midfrequencies of the spectrum, while SBR replicates higher frequency content by transposing up harmonics from the lower and midfrequencies at the decoder. Some guidance information for reconstruction of the high-frequency spectral envelope is transmitted as side information.
When needed, it also reconstructs or adaptively mixes in noise-like information in selected frequency bands in order to faithfully replicate signals that originally contained no or fewer tonal components.
The SBR idea is based on the principle that the psychoacoustic part of the human brain tends to analyse higher frequencies with less accuracy; thus harmonic phenomena associated with the spectral band replication process needs only be accurate in a perceptual sense and not technically or mathematically exact.
History and use
A Swedish company
Coding Technologies (acquired by
Dolby
Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in audio noise reduction, audio encoding/compression, spatial audio, and HDR imaging. Dolby licenses its technologies to ...
in 2007) developed and pioneered the use of SBR in its MPEG-2
AAC
AAC may refer to:
Aviation
* Advanced Aircraft, a company from Carlsbad, California
* Alaskan Air Command, a radar network
* American Aeronautical Corporation, a company from Port Washington, New York
* American Aviation, a company from Cleveland, ...
-derived codec called aacPlus, which first appeared in 2001. This codec was submitted to MPEG and formed the basis of MPEG-4
High-Efficiency AAC (HE-AAC), standardized in 2003. Lars Liljeryd, Kristofer Kjörling, and Martin Dietz received the
IEEE Masaru Ibuka Consumer Electronics Award
The IEEE Masaru Ibuka Consumer Electronics Award is a Technical Field Award of the IEEE given for outstanding contributions to consumer electronics technology. It is named in honor of Masaru Ibuka, co-founder and honorary chairman of Sony Cor ...
in 2013 for their work developing and marketing HE-AAC.
Coding Technologies' SBR method has also been used with
WMA 10 Professional to create WMA 10 Pro LBR, and with
MP3
MP3 (formally MPEG-1 Audio Layer III or MPEG-2 Audio Layer III) is a coding format for digital audio developed largely by the Fraunhofer Society in Germany, with support from other digital scientists in the United States and elsewhere. Orig ...
to create
mp3PRO.
It is used in broadcast systems like
DAB+
Digital radio is the use of digital technology to transmit or receive across the radio spectrum. Digital transmission by radio waves includes digital broadcasting, and especially digital audio radio services.
Types
In digital broadcasting sy ...
,
Digital Radio Mondiale
Digital Radio Mondiale (DRM; ''mondiale'' being Italian and French for "worldwide") is a set of digital audio broadcasting technologies designed to work over the bands currently used for analogue radio broadcasting including AM broadcasting—pa ...
(both DRM+ and DRM),
HD Radio
HD Radio (HDR) is a trademark for an in-band on-channel (IBOC) digital radio broadcast technology. It generally simulcasts an existing analog radio station in digital format with less noise and with additional text information. HD Radio is used ...
, and
XM Satellite Radio
XM Satellite Radio (XM) was one of the three satellite radio (SDARS) and online radio services in the United States and Canada, operated by Sirius XM, Sirius XM Holdings. It provided pay-for-service radio, analogous to subscription cable televisi ...
.
If the player is not capable of using the side information that has been transmitted alongside the "normal" compressed audio data, it may still be able to play the "baseband" data as usual, resulting in a dull (since the high frequencies are missing), but otherwise mostly acceptable sound. This is, for example, the case if an mp3PRO file is played back with MP3 software incapable of utilizing the SBR information.
See also
*
MPEG-4 Part 3
*
Psychoacoustics
Psychoacoustics is the branch of psychophysics involving the scientific study of sound perception and audiology—how humans perceive various sounds. More specifically, it is the branch of science studying the psychological responses associated ...
*
Spectral bands
External links
* Coding Technologies page describing SBR, as it appeared in 2007 at the Dolby acquisition
References
Audio codecs
{{Sound-tech-stub