|
|
MPEG-4 AAC-SSR
MPEG-4 AAC-SSR or MPEG-4 Advanced Audio Coding - Scalable Sample Rate was introduced by Sony to the MPEG-4 standard. The audio signal is first split into 4 bands using a 4 band polyphase quadrature filter bank. Then these 4 bands are further split using MDCTs with a size k of 32 or 256 samples. This is similar to normal MPEG-4 AAC which uses MDCTs with a size k of 128 or 1024 directly on the audio signal.
The advantage of this technique is that short block switching can be done separately for every PQF band. So high frequencies can be encoded using a short block to enhance temporal resolution, low frequencies can be still encoded with high spectral resolution. However, due to aliasing between the 4 PQF bands coding efficencies around (1,2,3) * fs/8 is worse than normal MPEG-4 AAC.
MPEG-4 AAC-SSR is very similar to ATRAC and ATRAC-3.
Why AAC-SSR was introduced The idea behind AAC-SSR was not only the advantage listed above, but also the possibility of reducing the data rate by removing 1, 2 or 3 of the upper PQF bands. A very simple bitstream splitter can remove these bands and thus reduce the bitrate and sample rate.
Example:
4 subbands: bitrate = 128 kbit/s, sample rate = 48 kHz, f_lowpass = 20 kHz 3 subbands: bitrate ~ 120 kbit/s, sample rate = 48 kHz, f_lowpass = 18 kHz 2 subbands: bitrate ~ 100 kbit/s, sample rate = 24 kHz, f_lowpass = 12 kHz 1 subband: bitrate ~ 65 kbit/s, sample rate = 12 kHz, f_lowpass = 6 kHz
Note: although possible, the resulting quality is much worse than typical for this bitrate. So for normal 64 kbit/s AAC a bandwidth of 14...16 kHz is achieved by using intensity stereo and reduced NMRs. This degrades audible quality less than transmitting 6 kHz bandwidth with perfect quality.
This article is licensed under the GNU Free Documentation License at http://www.gnu.org/copyleft/fdl.html
You may copy and modify it as long as the entire work (including additions) remains under this license.
You must provide a link to http://www.gnu.org/copyleft/fdl.html
To view or edit this article at Wikipedia go to http://www.wikipedia.org/wiki/MPEG-4_AAC-SSR
|
©
2005 Music
Entertainment Network. A Cyprus
Roussos Music Entertainment Company. All Rights Reserved.
Articles
from
Wikipedia
Encyclopedia
are licensed under the GNU Free Documentation License. You may copy and
modify it as long as the entire work (including additions) remains under
this license. You must provide a link to http://www.gnu.org/copyleft/fdl.html.
All text is available under the terms of the GNU Free Documentation License.
All trademarks and service marks including Napster,
Rio
MP3 Player, iRock,
Creative
MP3 Player, iRiver,
Apple iPod
Portable
MP3 Players + iTunes,
eMusic,
Guitar
Center Musicians
Friend, Zzounds
Musical Instrument Equipment Store, BMG
Music Service, Columbia
House DVD Club, eBay,
Amazon,
Netflix,
Jamster,
Gamefly,
Friendster,
Music123
Musical Instruments, Billboard,
MTV,
Yahoo
Launch, Overture
Yahoo Search Marketing, MusicMatch,
Kazaa,
Kazaa
Lite, Morpheus
software, Real
Rhapsody, Bose,
Sheet
Music Plus, Billboard
Magazine, Rolling
Stone Magazine, Walmart
Downloads, Barnes
and Noble book store, CDUniverse,
Tower
Records, MSN
Music, MySpace,
Limewire,
WinMX,
Google
Adsense, Alibris,
TicketsNow,
MusicSpace,
uBid
are property of their respective owners. Music.us has no affiliation with
MySpace
or Friendster,
but offers alternative services. Disclaimer: Uploading or downloading
of copyrighted works without permission or authorization of copyright
holders may be illegal and subject to civil or criminal liability and
penalties. Please buy
music and refrain from any illegal downloading activity. User
submitted free content, including Wikipedia encyclopedia or modification
thereof by end users, do not reflect the views and opinions of Music.us
and are for educational and research development purposes. Our website
offers advanced search for bands and artists bio and albums and browse
options for artist band biographies resources and information. We offer
blogs and community building tools for authors, bands and users. The Music.us
Entertainment Network is web's most comprehensive one-stop shopping, community
networking and education site. Find song lyrics, guitar tablature, posters,
ring tones, free MP3 downloads and hourly updating news feeds on musicians
and any genre style including rock,
pop,
hip
hop, country,
christian,
rap,
classical,
folk,
dance,
latin,
R
and B, blues,
punk,
heavy
metal, alternative,
guitar,
bass,
drums,
gospel,
wedding,
arabic,
jazz,
soundtrack,
world,
reggae,
soul
and more. Privacy Policy
- Site Map
- MP3 - Music Downloads
- Song Lyrics
| |
