A Quick "Rip" Through Digital Audio File Formats
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Although a lot of different file formats have been used to store digital sound, music, and even instrument or synthesizer tracks on computers, those seeking to store digital audio for playback will find their choices more limited. To some extent, such limitations occur as a function of the output device you want to use (for example, most RAM- or disk-based digital music players don't accommodate numerous formats).
Other factors worth considering include overall sound quality, the presence or absence of other digital versions of the same music, the types of players you want to use, and trade-offs between file sizes (smaller files mean more music) and listening quality (more compression normally means lower audio fidelity). It might also be worth factoring in whether you're rescuing sounds from potential oblivion (as might be the case for aging 8-track or cassette tapes that do become unlistenable and sometimes even unplayable after enough time).
Some compression schemes are "lossy," which means that once a file has been compressed it can't be returned to its original uncompressed form from the contents of the compressed file. Mathematically, this is a one-way, irreversible transformation. Other compression schemes are "lossless," which means that a uncompressed version of data can be generated from the compressed form. Mathematically, this is a two-way, reversible transformation. Lossy compression schemes usually result in smaller compressed files since they can "throw away" details and information they can't use and don't need, whereas lossless compression schemes produce bigger result files.
Another key ingredient in audio compression schemes is a special piece of software called a codec, short for the type of "compression/decompression" algorithm that's used to translate uncompressed data into a compressed form for storage, and to decompress that compressed form for access or playback. Web site Codec Central is a great repository of information that talks about codecs of all kinds, including those used for audio formats.
Common Digital Audio Formats
Table 1 provides an alphabetized list of the most common digital audio file formats. It also gives some indication of the age of each format, tells whether it supports compression, and gives a general indication of sound quality based on numerous audio tests and listening sessions (see the resources in Table 2 for pointers to more details on this and other topics).
Table 1: Common Digital Audio Formats
|
Name |
Ext |
Date |
Type |
Cmp |
Notes |
|
Advanced Audio Coding |
aac |
1997 |
Lossy |
Yes |
Also known as MPEG-4 AAC. Supports various compression rates (best known for iPod use). |
|
Audio Interchange File Format |
aiff |
1999 |
Lossless+ |
No |
Original, uncompressed Mac sound file format (not used in devices). |
|
Compact Disk Digital Audio (CD-DA) |
cda |
1979 |
Lossless+ |
No |
Standard digital audio CD format, uncompressed (not used in many devices except CD players). |
|
mp3PRO |
mp3 |
2001 |
Lossy |
Yes |
Improved version of MP3, still compressed (not supported on many devices). |
|
MPEG-1 Level 3 (MP3) |
Varies |
1993 |
Lossy |
Yes |
Uses perceptual coding to compress signals at various compression rates (supported on most devices). |
|
OGG Vorbis |
ogg |
2000 |
Lossy |
Yes* |
Open-source codec and audio-compression scheme (supported on some devices). |
|
QuickTime Audio |
mov |
1997 |
Lossy |
Yes |
Same MPEG-4 technology as AAC, in different multimedia wrapper (not used in devices). |
|
Real Audio Media |
rma |
1995 |
Lossy |
Yes |
Proprietary, compressed audio format (not used in devices). |
|
Waveform sound files |
wav |
1991 |
Lossless+ |
No |
Used for system sounds on Windows PCs (not used for hi-fi music or in devices). |
|
Windows Media Audio |
wma |
1997 |
Lossy+ |
Yes |
Offers various rates or no compression (supported on most devices). |
Notes
Ext = file extension, the three- or four-characters that follow file names in Windows environments.
Asterisk(*) indicates that various compression rates are supported
Plus (+) indicates that the format uses lossless compression, or supports an uncompressed (lossless) form.