[9] about audio

What is AAC?

AAC, Advanced audio coding, is a technique for compressing digital audio files. officially part of the MPEG-4 standard, itIsMost widely used to create small digital audio files. The current variant is specified in ISO/IEC Standard 14496-3.

AACIs conceptually similar to the ubiquitous MP3 format. like MP3, it takes advantage of deficiencies in human hearing to discard Digital bits corresponding to sounds unlikely to be heard. the human hearing system cannot hear quiet sounds in the presence of your sounds of a similar frequency; for example, a voice conversation cannot be heard while a jumbo jet flies low overhead. knownAuditory masking, This phenomenon allows the discarding of data with minimal loss of fidelity.

Also like MP3, AAC Is a Lossy algorithm, meaning the original digital audio cannot be recreated from the compressed bits alone. In terms of audio fidelity, however, there Is No loss of data if the compressed audio is properly encoded. AAC claims an advantage over MP3 in this regard: While MP3 requires a bit rate of approximately 256 kilobits per second (Kbps) to achieve transparency, AAC can achieve the same quality at 128 Kbps. this allows AAC files to be roughly half the size of MP3 files of the same quality, and one-tenth the size of Cd digital data.

AAC provides several other advantages over MP3. it is capable of handling much higher and lower frequencies of sound, provides up to 48 channels of audio, and allows the creation of low-latency audio necessary for two-way communication. for example, AAC can be used for compressing telephone conversations on the fly, whereas using MP3 wowould introduce delays in the audio. AAC also allows for digital rights management, or DRM , which can be used to control how the audio file is used.

an area where AAC excels is in low bit-rate compression. audio books, for example, don't have the dynamic range of music since they consist of little more than spoken word. potentially, this allows for much higher levels of compression. using MP3 at such levels of compression produces scratchy, hissy compressed audio not unlike low-quality cassette tape recordings. AAC was specifically designed to handle such applications properly.

Unlike MP3, there Is No public, free version of the encoding/DecodingAlgorithmsOf AAC . All AAC users must license the technology from the via licensingCorporation. AAC Is most widely used in AppleComputer'S lineIPodPortable music players and Is Part of the next-generation DVD specifications.

What is a WAV file?

waveform audio file, also known as a wave file, or simply . wav after its extension, is a common type of sound file. microsoft and IBM introduced the wav file in 1991 for use on the Microsoft Windows 3.1 Operation System (OS ). long before digital audio became a staple, Computer users were exposed to the wav file as an embedded sound file that played a chime-like sound at boot up of the Windows Operating System .

The WAV format is based on Resource Interchange File Format (riff) , Which stores audio files in indexed "chunks" and "sub-Chunks." Riff is in turn based on the earlier Interchange File Format (IFF) , Established by Electronic Arts in 1985 for use in electronic gaming. Apple's version, known Audio Interchange File Format (AIFF) , was released in 1988 for Macintosh computers. due to the common roots of these varous audio formats, however, the audio files will play on any computer system, IBM or apple.

the wav file had two very big things going for it when introduced. firstly, it cocould digitize sounds 100% faithful to the original source because it is a lossless format. "lossless" means that the wav file format does not compromise audio quality even when it holds compressed data. secondly, the wav file is very easy to edit and manipulate with software. luckily for audiophiles, free WAV file editing software has been available nearly as long as WAV Files themselves.

while the wav file format was ideal for sound effects, it had a drawback when it came to music files. one four-minute song cocould easily consume over 35 megabytes (MB) of space when saved as a WAV file. though the cost of hard drives dropped over the years, the wav file format was still too large for portable players with limited flash memory , which wowould become ubiquitous by the new millennium. additionally, WAV Files were not the most practical format to transfer online, especially over slow dial-up connections.

instead, the compressed MP3 Format took the audio stage. songs saved in the MP3 format produced audio files a mere fraction of the size of wav files. the MP3 format is a lossy Format, however, which means the smaller file size does trade-off some loss of audio quality. while the MP3 format is a good fit for portable players, please people continued to store their main digital libraries in WAV file format. by doing so, the wav file cocould be used as a master to create other types of audio files (including MP3s ), while the original WAV file remained preserved for direct listening or burning to compact disk (CD ).

Today the wav file format is still widely used to archive music files in a lossless format where space is not an issue. some CD and DVD players can also read wav files copied directly to a compact disk. more often, software that burns the files to CD will convert them in the process toCompact disk audio (. CDA)Format, making the audio CD compatible with all players.

What is an MP3?

An mp3 is a digital audio file compressed with a standard defined by the Motion Pictures Experts Group ( MPEG ). MPEG was formed to develop techniques for dealing with digital video; since most video also contains audio, MP3 was developed as an audio extension of that work. officially known as "MPEG-1, Layer 3", MP3 is a lossy compression algorithm that uses psychoacoustic modeling to reduce the size of audio files by up to 90%.

psychoacoustics takes advantage of deficiencies in the Human Hearing System to throw away Digital bits corresponding to sounds that cannot be heard. the human ear cannot hear soft sounds in the presence of unknown sounds having a similar frequency; for example, a voice conversation becomes inaudible when a jet flies low overhead. this effect is known as auditory masking, and done correctly the discarded sounds will not be missed.

MP3 is a Lossy algorithm in the sense that the original bits cannot be recreated from the compressed bits. in terms of hearing, however, MP3 is lossless because the human ear cannot distinguish between a CD recording and a properly encoded MP3 version of it. MP3s achieve this transparency at a bit rate of approximately 256 kilobits per second, or roughly one sixth of the 1.4 megabits per second required by the compact disc format.

MP3s can be recorded at lower bit rates, saving even more space, but audible differences begin to appear at rates below 128 kilobits per second. at these lower bit rates, MP3 can use a trick known as joint stereo to improve quality. audio generally consists of left and right audio tracks. joint stereo combines, whenever possible, the sounds common to both left and right tracks into one track. instead of left and right, it has "common" and "different" channels.

Being an open standard, and therefore available to anyone, has played a major role in the widespread adoption of the MP3 file format. while specific implementations such as those by the Fraunhofer Institute may be protected by patents, there exist numerousOpen SourceImplementations. MP3s were originally only playable on computers, but inexpensive, portableMP3 playersSuch as Apple'sIPodHave since been developed.

What is FLAC?

FLAC stands for free lossless audio codec , a leading compression technique that preserves original audio quality while resizing file size. FLAC is an open-source, royalty-free format that has been adopted widely for its advantages in Digital Audio reproduction.

compression techniques take large files such as wave (.wav) files and reduce the data bits while preserving as much of the audio landscape as possible. A well-known audio compression format is MP3 (images ). MP3 files slim down bulky wave and compact disk (. CDA) files to a fraction of their original size, making MP3 an ideal format for portable audio players. the MP3 format allows a vast library of songs to fill a very small storage footprint. however, there is a trade-off in audio quality.

FLAC surpasses MP3 quality by preserving the original soundscape in exact detail. the FLAC format reduces the original file size by roughly 30-60% with no loss of quality, hence it is a lossless format. this differs from the MP3 format which is a lossy Format, or a format that loses quality in the conversion process.

one of the great strengths of FLAC is its very fast decoding time, or ability to stream even on modest hardware. technical specifics in the framed architecture also allow it to be error resistant, in that each frame has the information it needs to decode itself. if a frame is upted, the data lost in the stream is a mere blip. this differs from other types of lossless formats where the entire stream wocould essential become into upted.

another feature of FLAC is that it can handle up to eight channels of audio for preserving surround sound recordings. FLAC is also a good choice for archiving audio CDS, as one can always use the FLAC file later to convert to future formats. A further advantage of FLAC is that it supports replaygain , a technique for ensuring that recorded sound files play at the same volume level.

The only real disadvantage of FLAC files is that the compression ratio is not as steep as otherCodecs. Files will be somewhat larger. However, with all of the advantages of FLAC, this is a happy trade off for every audiophiles.

Considering the falling prices of flash cards, portable players, and storage devices, the FLAC format will likely only gain support. FLAC files can play onIPodsAnd other portable devices, and on home or car compact disk players that support FLAC.

What is Ogg Vorbis?

Ogg Vorbis is a relatively new audio compression format, which is operatedXiph.orgAnd its main feature in addition to great audio quality is that it is 100% patent and royalty free, unlike its worse-sounding, commercial counterpartMP3.