Spectral band replication
Encyclopedia
Spectral band replication (SBR) is a technology to enhance audio or speech codecs, especially at low bit rate
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.
to create MPEG-4
High Efficiency AAC (HE-AAC
), with MP3
to create mp3PRO
, and with MPEG-1 Layer II (MP2). It was published for MPEG-4 Audio (MPEG-4 Part 3
) in ISO/IEC
14496-3:2001/Amd 1:2003 and defined as one of the MPEG-4 Audio Object Types.
It is used in broadcast systems like DAB+, Digital Radio Mondiale
(DRM+, not DRM), HD Radio
, and XM Satellite Radio
.
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 side information.
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
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.
Psychoacoustical codecs using SBR
SBR has been combined with AAC LCAdvanced Audio Coding
Advanced Audio Coding is a standardized, lossy compression and encoding scheme for digital audio. Designed to be the successor of the MP3 format, AAC generally achieves better sound quality than MP3 at similar bit rates....
to create MPEG-4
MPEG-4
MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...
High Efficiency AAC (HE-AAC
HE-AAC
High-Efficiency Advanced Audio Coding is a lossy data compression scheme for digital audio defined as a MPEG-4 Audio profile in ISO/IEC 14496-3. It is an extension of Low Complexity AAC optimized for low-bitrate applications such as streaming audio...
), with MP3
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
to create mp3PRO
Mp3PRO
mp3PRO is an audio compression algorithm that combines the MP3 audio format with spectral band replication compression methods. It claims to achieve transparency at lower bitrates than MP3, resulting in a file nearly half the size of standard MP3...
, and with MPEG-1 Layer II (MP2). It was published for MPEG-4 Audio (MPEG-4 Part 3
MPEG-4 Part 3
MPEG-4 Part 3 or MPEG-4 Audio is the third part of the ISO/IEC MPEG-4 international standard developed by Moving Picture Experts Group. It specifies audio coding methods...
) in ISO/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
14496-3:2001/Amd 1:2003 and defined as one of the MPEG-4 Audio Object Types.
It is used in broadcast systems like DAB+, Digital Radio Mondiale
Digital Radio Mondiale
Digital Radio Mondiale is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcasting, particularly shortwave...
(DRM+, not DRM), HD Radio
HD Radio
HD Radio, which originally stood for "Hybrid Digital", is the trademark for iBiquity's in-band on-channel digital radio technology used by AM and FM radio stations to transmit audio and data via a digital signal in conjunction with their analog signals...
, and XM Satellite Radio
XM Satellite Radio
XM Satellite Radio is one of two satellite radio services in the United States and Canada, operated by Sirius XM Radio. It provides pay-for-service radio, analogous to cable television. Its service includes 73 different music channels, 39 news, sports, talk and entertainment channels, 21 regional...
.
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 side information.