Re: MP3 - WAV and all that
Date: October 20, 2005 17:26
WAV (or WAVE), short for WAVE form audio format, is a Microsoft and IBM audio file format standard for storing audio on PCs. It is a variant of the RIFF bitstream format method for storing data in "chunks", and thus also close to the IFF and the AIFF format used on Macintosh computers. It takes into account some peculiarities of the Intel CPU such as little-endian byte order. The RIFF format acts as a "wrapper" for various audio compression codecs. It is the main format used on Windows systems for raw audio.
Though a WAV file can hold audio compressed with any codec, by far the most common format is pulse-code modulation audio data. Since PCM uses an uncompressed, lossless storage method which keeps all the samples of an audio track, professional users or audio experts may use the WAV format for maximum audio quality. WAV audio can also be edited and manipulated with relative ease using software.
WAV files can be used as an intermediary storage type for ripping songs from cassette tapes. People using Windows's Sound Recorder can redirect the output from their old Walkman-type cassette players's ear phone jacks to the PC audio input jacks via an audio cable. Although Sound Recorder can only record for 60 seconds, there are easy ways to lengthen the file for long songs or even the entire tape (record something, choose decrease speed from the effects menu, repeat until file is sufficiently long, and then record over it from the beginning). The WAV file is then converted via freeware packages to other, more compact formats.
As file sharing over the Internet has become popular, the WAV format has declined in popularity, primarily because uncompressed WAV files are quite large. More frequently, compressed but lossy formats such as MP3, Ogg Vorbis and Advanced Audio Coding are used to store and transfer audio, since their smaller file sizes allow for faster transfers over the Internet, and large collections of files consume only a conservative amount of disk space. There are also more efficient, lossless codecs available, such as Monkey's Audio, TTA, WavPack, FLAC, Shorten, Apple Lossless and WMA Lossless.
The WAV format is limited to files that are less than 2 GiB in size, due to the way its 32-bit file size header is read by most programs. Although this is equivalent to more than 3 hours of CD-quality audio (44.1 kHz, 16-bit stereo), it is sometimes necessary to go over this limit. The W64 format was created for use in Sound Forge. This format can be converted using the LGPL libsndfile library.
Contrary to the popular misconception, audio CDs do not use WAV as their storage format. The commonality is that both audio CDs and WAV files have the audio data encoded in PCM, but WAV is a data file format for computer use; if you rip an audio CD to WAV files and burn them onto a CD-R as a data disc (ISO) and insert it into a player that can handle only audio CDs, the CD will not play.
MP3 is a popular digital audio encoding and lossy compression format invented and standardised in 1991 by a team of engineers working in the framework of the ISO/IEC MPEG audio committee under the chairmanship of Professor Hans Musmann (University of Hannover - Germany). It was designed to greatly reduce the amount of data required to represent audio, yet still sound like a faithful reproduction of the original uncompressed audio to most listeners. In popular usage, MP3 also refers to files of sound or music recordings stored in the MP3 format on computers.
The name is derived from "MPEG-1 Audio Layer 3" more formally known as ISO/IEC 11172-3 Layer 3. The files recorded in this format are saved with the .mp3 filename extension. This extension is also sometimes shared by audio files encoded using the newer MPEG-2 Audio Layer 3 standard. The invention of this file extension name (.mp3) would be due to the FhG institute.
MP3 is a lossy compression format. It provides a representation of pulse-code modulation-encoded (PCM) audio data in a much smaller size by discarding portions that are considered less important to human hearing (similar to JPEG, a lossy compression for images).
A number of techniques are employed in MP3 to determine which portions of the audio can be discarded, including psychoacoustics. MP3 audio can be compressed with different bit rates, providing a range of tradeoffs between data size and sound quality.
The MP3 format uses, at its heart, a hybrid transform to transform a time domain signal into a frequency domain signal:
* 32 band polyphase quadrature filter
* 36 or 12 tap MDCT; size can be selected independent for sub-band 0...1 and 2...31
* aliasing reduction postprocessing
MP3 Surround, a version of the format supporting 5.1 channels for surround sound, was introduced in December 2004. MP3 Surround is backward compatible with standard stereo MP3, and file sizes are similar.
In terms of the MPEG specifications, AAC (Advanced audio coding) from MPEG-4 is to be the successor of the MP3 format, although there has been a significant movement to create and popularize other audio formats. Nevertheless, any succession is not likely to happen for a significant amount of time due to MP3's overwhelming popularity (MP3 enjoys extremely wide popularity and support, not just by end-users and software but by hardware such as DVD and CD players).
CONCLUSION TO THIS LONG AND BORING STORY:
WAV is a raw audiofile without quality loss of the original recording. MP3 (unlike FLAC) has a loss of quality, and although this loss may be small and may appear unhearable for a leek, bootlegs must not be spreaded in this format.