- aac: the Advanced Audio Coding format is based on the mpeg4 audio standard owned by Dolby. A copy-protected version of this format has been developed by Apple for use in music downloaded from their iTunes Music Store.
- aif: the standard PCM (uncompressed, CD-quality) audio file format used by Apple.
- au: the standard audio file format used by Sun, Unix and Java. The audio files can be PCM or compressed with the ulaw, alaw or G729 codecs.
- mp3: the MPEG Layer-3 format is the most popular format for downloading and storing music. By eliminating portions of the audio file that are essentially inaudible, mp3 files are compressed to roughly one-tenth the size of an equivalent PCM file while maintaining good audio quality. The mp3 format is not that good for voice storage.
- ogg: a free, open source container format supporting a variety of codecs, the most popular of which is the audio codec Vorbis. Vorbis files are often compared to mp3 files in terms of quality. But the simple fact that mp3 are so much more broadly supported makes it difficult to recommend ogg files.
- flac: a lossless compression codec. If you compress a PCM file to flac and then restore it again, it will be a perfect copy of the original. All the other codecs discussed here are lossy which means a small part of the quality is lost. The cost of this losslessness is that the compression ratio is not good. flac is good for archiving PCM files where quality is important.
- gsm: designed for telephony use in Europe, gsm is a very practical format for telephone quality voice. It makes a good compromise between file size and quality. Note that wav files can also be encoded with the gsm codec.
- ra: a “Real Audio” format designed for streaming audio over the Internet. The .ra format allows files to be stored in a self-contained fashion on a computer, with all of the audio data contained inside the file itself.
- ram: a text file that contains a link to the Internet address where the “Real Audio” file is stored. The .ram file contains no audio data itself.
- raw: a raw file can contain audio in any codec but is usually used with PCM audio data. It is rarely used except for technical tests.
- wav: the standard PCM (uncompressed, CD-quality) audio file format used in Windows PCs. They can be large in size, around 10MB per minute of music. It is less well known that wave files can also be encoded with a variety of codecs to reduce the file size (for example the gsm or mp3 codecs).
- wma: the popular Windows Media Audio format owned by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection.
About the Author:
Daniel Fournier has vast experience in acoustics, audio engineering techniques, hardware, recording, computer science, mathematics, software, physiques and Sonology. He offers musical and technical expertise, well trained ears and in his words, “a faithful documentation of the sounds conceived by artists”. His clients include Sony Tokyo, Austep Music, ABC radio, and various Australian and International artists.