Music File Formats and Codecs Explained

There are many proprietary file formats that are native to specific audio software, particularly in the field of audio production, but the following list covers the most common music file formats and codecs used by most computer systems and audio software.Typically compressed formats are:

1. MP3. The revolution in digital audio has been led by one specific audio file format called MPEG Audio Layer 3, or MP3. Based on a series of international standards of audio and video compression called MPEG (Moving Picture Experts Group), MP3 is a file format that allows audio data to be digitally compressed to a chosen degree by compressing or simplifying parts of the music that are perceived less by the human ear. Generally speaking, the higher the compression, the lower the quality of the compressed audio; nevertheless, even at near CD quality, using a bit rate of 128kbps (kilobits per second; that is using 128,000 bits of data to represent each second of music), MP3 encoded audio is about one twelfth the size of ordinary uncompressed audio.

This is important, because it allows the transfer of high quality audio data over networks or the Web in a fraction of the time it normally would; as such, MP3 files are currently the standard for the online broadcast of music. Plus, it allows for many more songs to be stored on a hard drive or memory chip.

This makes the sale of music on a downloadable, song by song basis possible and economically viable, and it allows personal music players to store a huge volume of digital audio. It also makes piracy of the type that used to happen with dual cassette decks much easier and more widespread, but fortunately, many record labels have reported increased sales as a result of giving away MP3 tracks on their websites. This could be due to the fact that word of mouth has increased interest and demand all over the world, but in any event, artists, distributors, and companies must continue to adapt. The technology is only going to get more powerful with the integration of Surround capability and other innovations.

2. WMA or ASF. The Windows Media Audio format is Microsoft's competitor to MP3. It is often contained within an Advanced Systems File (ASF) if it includes other information as well as audio. The latest versions offer surround sound and digital rights management (anti-piracy) support.

3. AAC. Advanced Audio Coding is Apple's offering as a competitor to MP3 and is used by iTunes and QuickTime. This use the audio based portions of MPEG-4 media standards, agreed upon by the Moving Picture Experts Group and usually has an .M4A file extension.

4. OGG. OGG Vorbis is a patent free format developed by the Xiph Open Source Community, part of a non profit corporation "dedicated to protecting the foundations of Internet multimedia from control by private interests." The files are inherently variable bit rate and can be encoded on a scale of quality from one to ten, with six being roughly CD quality and three being the competitive equivalent to a 128kbps MP3.

5. ATRAC. Adaptive Transform Acoustic Coding is a compression algorithm developed by Sony for use on Minidiscs and other devices. It may include OpenMG which has a digital rights management scheme developed by Sony. These files will have .OMG or .OMA extensions.

6. RealAudio. A format designed by RealNetworks for streaming over the Internet, which uses various compression codecs and will have the file extension .RA, .RM, or .RAM.

7. AC-3. Adaptive Transform Coder 3 the codec commonly known as Dolby Digital. It is a standard for audio on DVDs.

8. MP4. A "container" file format based on MPEG4 audio and video standards that can include various forms of media, including MP3 based audio.

Typically uncompressed formats are:

1. WAV or WAVE. The Windows wave file is the generic audio format on Windows PCs, using Pulse Code Modulation (PCM) to represent the audio in basic binary, this is not unlike the way a generic text file is stored, as it is uncompressed and can be read by any computer. It can allow various sample sizes at various sample rates; CD quality audio requires a sample rate of 44.1 kHz and a sample size or bit depth of 16 bits, meaning that the audio is represented, or "captured," 44,100 times per second using samples of 16 bits at a time.

There are various compression schemes that can be used to reduce the size of WAV files, but these tend to reduce compatibility with some programs or systems, and they are not as effective as MP3.

Professional audio applications offer the ability to process (open and edit) or render (save) WAV files at higher sample rates and bit depths, popularly, 24-bit samples at 96kHz but this requires a sound card that will support these files as well as a powerful computer.

2. AIFF or AIF. The Audio Interchange File Format was developed by Apple and is equivalent to Microsoft's WAV format, also using the PCM codec.

3. AU. The Sun Microsystems default format is equivalent to WAV or AIFF and readable on most platforms.

4. CDDA or CDA. The PCM based format for CD audio is limited to a sample rate of 44.1 kHz and a sample size of 16 bits.