WAV
From Wikipedia, the free encyclopedia
 |
|
| Filename extension | .wav |
|---|---|
| Internet media type | audio/wav |
| Type code | WAVE |
| Uniform Type Identifier | com.microsoft.waveform-audio |
| Developed by | Microsoft & IBM |
| Type of format | audio file |
| Extended from | RIFF |
WAV (or WAVE), short for Waveform audio format, is a Microsoft and IBM audio file format standard for storing an audio bitstream on PCs. It is an application of the RIFF bitstream format method for storing data in “chunks”, and thus also close to the IFF and the AIFF format used on Amiga and Macintosh computers, respectively. It is the main format used on Windows systems for raw and typically uncompressed audio. The usual bitstream encoding is the Pulse Code Modulation (PCM) format.
Contents |
[edit] Description
Both WAVs and AIFFs are compatible with Windows and Macintosh operating systems. The format takes into account some differences of the Intel CPU such as little-endian byte order. The RIFF format acts as a “wrapper” for various audio compression codecs.
Though a WAV file can hold compressed audio, the most common WAV format contains uncompressed audio in the linear pulse code modulation (LPCM) format. The standard audio file format for CDs, for example, is LPCM-encoded, containing two channels of 44,100 samples per second, 16 bits per sample. Since LPCM 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. The WAV format supports compressed audio, using, on Windows, the Audio Compression Manager. Any ACM codec can be used to compress a WAV file. The UI for Audio Compression Manager is accessible by default through Sound Recorder.
Beginning with Windows 2000, a WAVE_FORMAT_EXTENSIBLE header was defined which specifies multiple audio channel data along with speaker positions, eliminates ambiguity regarding sample types and container sizes in the standard WAV format and supports defining custom extensions to the format chunk.
[edit] Popularity
Uncompressed WAV files are quite large in size, so, as file sharing over the Internet has become popular, the WAV format has declined in popularity. However, it is still a commonly used, relatively “pure”, i.e. lossless, file type, suitable for retaining “first generation” archived files of high quality, or use on a system where high fidelity sound is required and disk space is not restricted.
More frequently, the smaller file sizes of compressed but lossy formats such as MP3, ATRAC, AAC, (Ogg)Vorbis and WMA are used to store and transfer audio. Their small file sizes allow faster Internet transmission, as well as lower consumption of space on memory media. However, lossy formats trade off smaller file size against loss of audio quality, as all such compression algorithms compromise available signal detail. There are also more efficient lossless codecs available, such as FLAC, Shorten, Monkey's Audio, ATRAC Advanced Lossless, Apple Lossless, WMA Lossless, TTA, and WavPack, but none of these is yet a ubiquitous standard for both professional and home audio.
The usage of the WAV format has more to do with its familiarity, its simplicity and simple structure, which is heavily based on the IFF file format. Because of this, it continues to enjoy widespread use with a variety of software applications, often functioning as a 'lowest common denominator' when it comes to exchanging sound files between different programs.
In spite of their large size, uncompressed WAV (though that format can be different from the Microsoft WAV) files are sometimes used by some radio broadcasters, especially those that have adopted the tapeless system. BBC Radio in the UK uses 44.1 kHz 16 bit two channel .wav audio as standard in their VCS system. The ABC "D-Cart” system, which was developed by the Australian broadcaster, also uses a non-compressed format to preserve sound quality, and it has become more economical as the cost of data storage has dropped. In the system of “D-Cart”, the sampling rate of WAV files is usually at a 48 kHz 16 bit two channel, which is identical to that of the Digital Audio Tape.
[edit] Limitations
The WAV format is limited to files that are less than 4 GB in size, because of its use of a 32-bit unsigned integer to record the file size header (some programs limit the file size to 2–4 GB).[2] Although this is equivalent to about 6·6 hours of CD-quality audio (44.1 KHz, 16-bit stereo), it is sometimes necessary to exceed this limit, especially when greater sampling rates or bit resolutions are required. The W64 format was therefore created for use in Sound Forge. Its 64-bit header allows for much longer recording times. The RF64 format specified by the European Broadcasting Union has also been created to solve this problem.
[edit] Audio CDs
Audio CDs do not use WAV as their sound format, using instead Red Book audio. The commonality is that both audio CDs and WAV files have the audio data encoded in PCM. WAV is a data file format for a computer to use that can't be understood by CD players directly. To record WAV files to an Audio CD the file headers must be stripped and the remaining PCM data written directly to the disc as individual tracks with zero padding added to match the CD's sector size.
[edit] WAV file compression codecs compared
As mentioned wav files can be encoded with a variety of codecs to reduce the file size (for example the GSM or MP3 codecs).
This is a reference to compare the monophonic (not stereophonic) audio quality and compression bitrates of the different codecs available for .wav files including PCM, ADPCM, GSM, CELP, SBC, TrueSpeech and MPEG Layer-3.
| Format | Bitrate | 1 Minute = | Sample |
|---|---|---|---|
| 11,025 Hz 16 bit PCM | 176.4 kbit/s[3] | 1292 KiB[4] | 11k16bitpcm.wav |
| 8,000 Hz 16 bit PCM | 128 kbit/s | 938 KiB | 8k16bitpcm.wav |
| 11,025 Hz 8 bit PCM | 88.2 kbit/s | 646 KiB | 11k8bitpcm.wav |
| 11,025 Hz µ-Law | 88.2 kbit/s | 646 KiB | 11kulaw.wav |
| 8,000 Hz 8 bit PCM | 64 kbit/s | 469 KiB | 8k8bitpcm.wav |
| 8,000 Hz µ-Law | 64 kbit/s | 469 KiB | 8kulaw.wav |
| 11,025 Hz 4 bit ADPCM | 44.1 kbit/s | 323 KiB | 11kadpcm.wav |
| 8,000 Hz 4 bit ADPCM | 32 kbit/s | 234 KiB | 8kadpcm.wav |
| 11,025 Hz GSM6.10 | 18 kbit/s | 132 KiB | 11kgsm.wav |
| 8,000 Hz MP3 16 kbit/s | 16 kbit/s | 117 KiB | 8kmp316.wav |
| 8,000 Hz GSM6.10 | 13 kbit/s | 103 KiB | 8kgsm.wav |
| 8,000 Hz Lernout & Hauspie SBC 12 kbit/s | 12.0 kbit/s | 88 KiB | 8ksbc12.wav |
| 8,000 Hz DSP Group Truespeech | 9 kbit/s | 66 KiB | 8ktruespeech.wav |
| 8,000 Hz Mp3 8 kbit/s | 8 kbit/s | 60 KiB | 8kmp38.wav |
| 8,000 Hz Lernout & Hauspie CELP | 4.8 kbit/s | 35 KiB | 8kcelp.wav |
The above are WAV files — even if they use the MP3 codec they will have the “.wav” extension.
[edit] See also
- Audio Compression Manager
- Broadcast Wave Format (BWF)
- RF64, an extended file format for audio (multichannel file format enabling file sizes to exceed 4 gigabytes)
[edit] References
[edit] External links
- A summary of the WAVE file format
- Another summary of WAVE file format
- Basic WAV file format
- A detailed explanation of digital audio formats and best practices (pdf)
- WAVE_FORMAT_EXTENSIBLE Specification
- More information on WAVE_FORMAT_EXTENSIBLE
|
|||||||||||||||||||||||||||||||||||||||||||
