Brief explanation of Audio File Formats and CODECS

Brief explanation of Audio File Formats and CODECS

Audio Transmission

• Audio File Format
• An audio file format is a file for storing digital audio on a computer system. This data can be stored uncompressed or compressed to reduce the file size. It can be a raw bitstream, but it is usually a container format or an audio data with defined storage layer.
• Types of Formats
• It is important to distinguish between a file format and an audio codec. A codec performs the encoding and decoding of the raw audio data while the date itself is stored in a file with a specific audio file format. Although most audio file formats support only one type of audio data (create with an audio coder), a multimedia container format (as Mastroska or AVI) may support multiple types of audio and video data.

Uncompressed audio formats

   There is one major uncompressed audio format, PCM, which is usually stored in a .wav file on windows or in a .aiff on  Mac OS. The AIFF format is based on the Interchange File Format (IFF). The WAV format is based on the Resource Interchange File Format(RIFF), which is similar to IFF. WAV and AIFF are flexible file formats designed to store more or less any combination of sampling rates or bitrates. This makes them suitable file formats for storing and archiving an original recording. 

    BWF (Broadcast Wave Format) is a standard audio formats created by European Broadcasting Union as a successor to WAV. BWF allows metadata to be stored in the file. See European Broadcasting Union: Specification of the broadcast wave format (EBU Technical Document 3285, July 1997). This is the primary recording used in many professional audio workstations in the television and film industry. BTW files include a standardized timestamp reference which allows for easy synchronization with separate picture element. Stand-Alone, file based, multi-track recorders from sound Devices, Zaxcom, HHB USA, Fostex, and aaton all use BWF as their preferred format. 

    The .cda (Computer Disk Audio Tracks) is a small file that serves as a shortcut to the audio data for a track on a music CD. It does not contain audio and is therefore not considered to be a proper audio file format.

Lossless compressed audio formats

A lossless compressed format stores data in less space by eliminating unnecessary data. Uncompressed audio formats encode both sound and silence with the same number of bits per unit of time. Encoding an uncompressed minute of absolute silence produces a file of the same size as encoding an uncompressed minute of music. In a lossless compressed format, however, the music would occupy a smaller portion of the file and the silence would take up almost no space at all.

    Lossless compression formats enable the original uncompressed data to be recreated exactly. They include the common FLAC, WavPack, Monkey's audio, ALAC(Apple lossless). They provide a compression ratio of about 2:1 (i.e. their files take up half the space of the originals ). Development in lossless compression formats aims to reduce processing time while maintaining a good compression ratio.

Lossy compressed audio formats

    Lossy compression enables even greater reductions in file size by removing some of the data. Lossy compression typically achieves far greater compression but somewhat reduced quality than lossless compression by simplifying the complexities of the data. A variety of techniques are used mainly by exploiting psychoaccustics, to remove data with minimal reduction in the quality of reproduction. For many everyday listening situations, the loss in data(and thus quality) is imperceptible.

    The popular MP3 format is probably the best-known example, but AAC format found on the iTunes Music store is also common. Most formats offer a range of degrees of compression, generally measured in bit rate. The lower the rate, the smaller the file and the more significant  the quality loss.

CODEC

    A CODEC is a device or computer program capable of encoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly "coder-decoder". A codec should not be confued with a coding or compression format or standard - a format is a document, a way of storing data, while a codec is a program which can read or write such files. In practice "codec" is sometimes used loosely to refer to formats, however.

    A codec encodes a data stream or signal for transmission, storage or encryption, or decodes it for playback or editing. Codecs are used in video conferencing, streaming media and video editing applications. A video camera's Analog-to-Digital Converter (ADC) converts its analog signals into digital signals, which are then passed through a video compressor for digital transmission or storage. A receiving device then runs the signal through a video compressor, then a Digital-to-Analog Convertor (DAC) for analog display. The term codec is also used as a genric name for a video conferencing unit.

Media Codecs

    Codecs are often designed to emphasize certain aspects of the media , or their use to be encoded. For example, a digital video (using a DV codec) of a sports event needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to perform well encoding color and surface texture. 

    Audio codecs for cell phones need to have very low latency between source encoding and playback; while audio codecs for recording or broadcast can use high-latency audio compression techniques to achieve higher fidelity at a lower bit-rate. 

    There are thousands of audio and video codecs ranging in cost from free to hundreds of dolloars or more. This variety of codecs can create compatibility and obsolescenes issues. The impact is lessened for older formats, for which free or nearly-free codecs have existed for a long time.

    The older formats are ofter ill-suited to modern applications, however, such as playback in small portable devices. For example, raw uncompressed PCM audio (44.1 KHz, 16 bit sterero, as represented on an audio CD or in a .wav or .aiff file) has long been a standard across multiple platforms, but its transmission over networks is slow and expensive compared with more modern compressed formats, such as MP3.

    Many multimedia data streams contain both audio and video, and often some metadata that permit synchronization of audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data streams, to be useful in stored or transmitted form, they must be encapsulated together in a container format. When a user with a low-bitrate codec talks to a user with another codec, additional distortion is introduced by each transcoding.