MPEG-4 Part 3 (formally Logo of the International Organization for Standardization The International Organization for Standardization (ISO or Iso) is an international standard-setting body made up of representatives from national standards bodies. Founded in 1947 February 23, the organization produces world-wide industrial and commercial standards. While the ISO defines itself as a... ISO/ The International Electrotechnical Commission (IEC) is a standards organization dealing with electrical, electronic and related technologies. Many of its standards are developed jointly with the ISO. The IEC is made up of representatives of national standards bodies. The IEC was founded in 1906 and currently has more than 60 participating... IEC 14496-3) is, as the name suggests, the third part of the Logo of the International Organization for Standardization The International Organization for Standardization (ISO or Iso) is an international standard-setting body made up of representatives from national standards bodies. Founded in 1947 February 23, the organization produces world-wide industrial and commercial standards. While the ISO defines itself as a... ISO/ The International Electrotechnical Commission (IEC) is a standards organization dealing with electrical, electronic and related technologies. Many of its standards are developed jointly with the ISO. The IEC is made up of representatives of national standards bodies. The IEC was founded in 1906 and currently has more than 60 participating... IEC MPEG-4, introduced in 1998, is the designation for a group of audio and video coding standards agreed upon by the Moving Picture Experts Group (MPEG). MPEG-4 is primarily designed to handle low bit rate content, from 4,800 bit/s to approximately 4 Mbit/s. The primary uses... MPEG-4 international standard. It specifies Audio can mean: sound that can be heard electronics or other signals of frequencies audible to humans (about 20--20,000 Hz) broadcasting or reception of sound high-fidelity sound reproduction sound recording and reproduction in general I hear in Latin This is a disambiguation page — a navigational... audio The term coding has the following meanings: In communications systems, the altering of the characteristics of a signal to make the signal more suitable for an intended application, such as optimizing the signal for transmission, improving transmission quality and fidelity, modifying the signal spectrum, increasing the information content, providing error... coding methods.

The Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. AAC was designed to replace MP3. AAC, known formally as ISO/IEC 13818-7, was published in 1997 as an extension to the MPEG-2 international standard, ISO/IEC 13818-3. It was further improved in... Advanced Audio Coding in MPEG-4 Part 3 was enhanced relative to what was previously specified in MPEG-2 (1994) is the designation for a group of audio and video coding standards agreed upon by MPEG (Moving Pictures Experts Group), and published as ISO standard 13818. MPEG-2 is typically used to encode audio and video for broadcast signals, including digital satellite and Cable TV. MPEG-2... MPEG-2 Part 7, in order to provide better Sound quality generally refers to the quality of the audio output from various electronic devices. Sound quality can be defined as the degree of accuracy with which a device records or emits the original sound waves. This accuracy depends on the range of sound which is sampled, the rate at... sound quality relative to the bit rate used for the encoding.

One codec defined in MPEG-4 Part 3 is known as Low Complexity Advanced Audio Coding (LC-AAC). Another one is known as High-Efficiency Advanced Audio Coding (HE-AAC) or "aacPlus". Another one is known as Scalable Sample Rate Advanced Audio Coding ( 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... AAC-SSR).

aacPlus, or HE-AAC

aacPlus is a A lossy data compression method is one where compressing a file and then decompressing it retrieves a file that may well be different to the original, but is close enough to be useful in some way. This type of compression is used frequently on the Internet and especially in streaming... lossy data compression scheme for audio streams. It is based on MPEG-4, introduced in 1998, is the designation for a group of audio and video coding standards agreed upon by the Moving Picture Experts Group (MPEG). MPEG-4 is primarily designed to handle low bit rate content, from 4,800 bit/s to approximately 4 Mbit/s. The primary uses... MPEG-4, and combines three techniques: Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. AAC was designed to replace MP3. AAC, known formally as ISO/IEC 13818-7, was published in 1997 as an extension to the MPEG-2 international standard, ISO/IEC 13818-3. It was further improved in... Advanced Audio Coding (AAC), Spectral Band Replication or SBR is a technology to enhance audio or speech codecs especially at low bitrates. It can be combined with any audio compression codec: the codec transmits the lower frequencies of the spectrum and SBR reconstructs the higher frequencies based on the lower frequencies and transmitted side... Spectral Band Replication (SBR), and parametric stereo (PS).

aacPlus was standardized by the The Moving Picture Experts Group (MPEG) is a small group charged with the development of video and audio encoding standards. Since its first meeting in 1988, MPEG has grown to include approximately 350 members from various industries and universities. MPEGs official designation is ISO/IEC JTC1/SC29 WG11. MPEG... MPEG under the High Efficiency AAC (HE-AAC) name. The Codec is a portmanteau of coder/decoder, which describes a device or program capable of performing transformations on a data stream or signal. Codecs can both put the stream or signal into an encoded form (often for transmission, storage or encryption) and retrieve, or decode that form for viewing or... codec can operate at very low bitrates and is good for Web radio (or Internet radio) is a radio re-broadcasting service one can receive via the Internet. Because the radio signal is relayed over the Internet through the World Wide Web, it is possible to access the stations from anywhere in the world—for example, to listen to an... Internet radio streaming. A 48 kilobit-per-second stream is considered to have higher quality than 128 kbit/s MP3 (or, more precisely, MPEG-1/2 Audio Layer 3) is an audio compression algorithm capable of greatly reducing the amount of data required to reproduce audio, while sounding like a faithful reproduction of the original uncompressed audio to most listeners. History MPEG-1/2 Layer 2 encoding started in... MP3.

aacPlus is supported in the This article is about free software as defined by the Free Software Foundation. For software available free of charge, see Freeware. Free software is software which, once obtained, can be used, copied, studied, modified and redistributed. It is often made available online without charge or offline for the cost of... free FAAD2 decoding library, and hence in many free players, and in Winamp is a skinnable, multi-format music/media player made by Nullsoft. It is freeware, although a Pro version with faster CD read/write speeds is available for a small payment. Winamp gained popularity in the late 1990s, particularly with the proliferation of the MP3 audio format and the emergence... Winamp and The title given to this article is incorrect due to technical limitations. The correct title is foobar2000. foobar2000 is a freeware audio player for Windows developed by Peter Pawlowski, a former freelance contractor for Nullsoft. Featuring a standards-compliant, user-friendly interface, it also boasts many features for metadata support... foobar2000.

External links

• Tuner2.com (http://www.tuner2.com/) list of Internet radio stations using aacPlus
• aacPlus explained (http://www.codingtechnologies.com/products/aacPlus.htm)
• Open Source AAC codec (http://www.audiocoding.com/) FAAC (encoder) and FAAD2 (decoder)

MPEG-4 AAC-SSR

MPEG-4 AAC-SSR or MPEG-4 Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. AAC was designed to replace MP3. AAC, known formally as ISO/IEC 13818-7, was published in 1997 as an extension to the MPEG-2 international standard, ISO/IEC 13818-3. It was further improved in... 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 A polyphase quadrature filter, or PQF is a filter bank, which splits an input signal into a given number N (mostly a power of 2) of equidistant sub-bands. These sub-bands are subsampled by a factor of N, so they are critically sampled. This critical sampling introduces aliasing. Similar... polyphase quadrature filter bank. Then these 4 bands are further split using The modified discrete cosine transform (MDCT) is a Fourier-related transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where subsequent blocks are overlapped so that the last... MDCTs with a size k of 32 or 256 samples. This is similar to normal MPEG-4 AAC which uses The modified discrete cosine transform (MDCT) is a Fourier-related transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where subsequent blocks are overlapped so that the last... 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 (Adaptive TRansform Acoustic Coding) is an audio compression algorithm used to store information on Minidiscs and other Sony_branded audio players. First developed by Sony in 1991; the higher compression flavors of ATRAC3 and ATRAC3plus followed in 2000 and 2003, respectively. It uses quadrature mirror filters and modified discrete cosine... 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.

*.m4a

*.m4a is the A filename extension or filename suffix is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. It... file extension attached to names of files using the MPEG-4 Audio standard. The normal extension for any MPEG-4 file is MPEG-4 Part 14 or *.mp4, is a file format (a so called container) specified as a part of the ISO/ IEC MPEG-4 international standard. It is used to store media types defined by the ISO/ IEC Moving Picture Experts Group, and can be used to store other media... *.mp4, which is also mentioned in the MPEG-4 standard. The .m4a file extension has been popularized by Apple, which started using the .m4a file extension in their Screenshot of Mac OS X version of iTunes The title given to this article is incorrect due to technical limitations. The correct title is iTunes. iTunes is a computer program made by Apple Computer intended to play, organize and buy music files (it is also a common name for iTunes... iTunes software and The title given to this article is incorrect due to technical limitations. The correct title is iPod. A 4th Generation iPod, with earphones. The iPod has a multilingual interface, here using Dutch. The iPod family consists of a series of portable digital audio players (DAP) designed and marketed by Apple... iPod music players to distinguish between MPEG-4 Video and Audio files. Currently, most software that supports MPEG-4 Audio also supports the .m4a extension. The most common type of .m4a files available are those using the AAC ( Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. AAC was designed to replace MP3. AAC, known formally as ISO/IEC 13818-7, was published in 1997 as an extension to the MPEG-2 international standard, ISO/IEC 13818-3. It was further improved in... Advanced Audio Coding) audio format, but other formats such as Apple Lossless (also known as Apple Lossless Encoder or ALE) is an audio codec developed by Apple Computer for lossless encoding of digital music. Apple Lossless data is stored within an MP4 container with the filename extension .m4a. Contrary to popular belief, Apple Lossless is not a variant of AAC... Apple Lossless and even MP3 (or, more precisely, MPEG-1/2 Audio Layer 3) is an audio compression algorithm capable of greatly reducing the amount of data required to reproduce audio, while sounding like a faithful reproduction of the original uncompressed audio to most listeners. History MPEG-1/2 Layer 2 encoding started in... mp3 files may be put inside a .m4a container file. You can normally safely rename the file extension of a MPEG-4 Part 14 or *.mp4, is a file format (a so called container) specified as a part of the ISO/ IEC MPEG-4 international standard. It is used to store media types defined by the ISO/ IEC Moving Picture Experts Group, and can be used to store other media... *.mp4 file containing only audio to .m4a or vice versa to get the file to properly play in your favorite audio player.

Protected MPEG-4 Audio

When these files have Digital Rights Management or digital restrictions management (abbreviated DRM) is an umbrella term for any of several technical arrangements which empower a vendor of content in electronic form to control how the material can be used on any electronic device with such measures installed. The name rights management implies that... digital rights management (DRM) restrictions applied to them, their extension are changed to *.m4p, the p standing for protected. Music files purchased from the The title given to this article is incorrect due to technical limitations. The correct title is iTunes Music Store. iTunes Music Store The iTunes Music Store (iTMS) is a paid online music service run by Apple Computer. Introduced on April 28, 2003, the store, with generous restrictions on the uses... iTunes Music Store have this extension.

External links

• M4a.com (http://www.m4a.com/)
• Apple: MPEG-4: AAC (http://www.apple.com/mpeg4/aac/)
• AudioCoding.com Wiki (http://www.audiocoding.com/modules/wiki/?page=mp4)

See also

• MPEG-4 Part 2
• Digital Rights Management or digital restrictions management (abbreviated DRM) is an umbrella term for any of several technical arrangements which empower a vendor of content in electronic form to control how the material can be used on any electronic device with such measures installed. The name rights management implies that... Digital rights management
• Advanced Audio Coding (AAC) is a lossy data compression scheme intended for audio streams. AAC was designed to replace MP3. AAC, known formally as ISO/IEC 13818-7, was published in 1997 as an extension to the MPEG-2 international standard, ISO/IEC 13818-3. It was further improved in... Advanced Audio Coding