An audio file format is a container format for storing audio data on a computer system
Types of formats
It is important to distinguish between a file format and a codec.
A codec performs the encoding and decoding of the raw audio data while
the data itself is stored in a file with a specific audio file format.
Though most audio file formats support only one audio codec, a file format may support multiple codecs, as AVI does.
For podcasting and most of your work with audio files, you will work with two types:
NOTE: The portable audio recorders we are providing allow you to record for the most part directly to mp3, the file format supported by iTunes U uploads. This makes it very easy for you to record and simply upload to your iTunes U site. WAV files are much larger files and should be compressed to mp3 or other formats for listening online.
Uncompressed audio format
There is one major uncompressed audio format, PCM, which is usually stored as a .wav on Windows or as .aiff on Mac OS.
WAV is a flexible file format designed to store more or less any
combination of sampling rates or bitrates. This makes it an adequate
file format for storing and archiving an original recording. A lossless
compressed format would require more processing for the same time
recorded, but would be more efficient in terms of space used. WAV, like
any other uncompressed format, encodes all sounds, whether they are
complex sounds or absolute silence, with the same number of bits per
unit of time. As an example, a file containing a minute of playing by a
symphonic orchestra would be the same size as a minute of absolute
silence if they were both stored in WAV. If the files were encoded with
a lossless compressed audio format, the first file would be marginally
smaller, and the second file taking up almost no space at all. However,
to encode the files to a lossless format would take significantly more
time than encoding the files to the WAV format. Recently some new
lossless formats have been developed (for example TAK), which aim is to achieve very fast coding with good compression ratio.
The WAV format is based on the RIFF file format, which is similar to the IFF format.
Free and open file formats
- wav – standard audio file container format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM),
CD-quality sound files, which means that they can be large in size —
around 10 MB per minute. Wave files can also contain data encoded with
a variety of codecs to reduce the file size (for example the GSM or mp3
codecs). Wav files use a RIFF structure.
- ogg – a
free, open source container format supporting a variety of codecs, the
most popular of which is the audio codec Vorbis. Vorbis offers better
compression than MP3 but is less popular.
- Musepack or MPC (formerly known as MPEGplus, MPEG+ or MP+) is an open
source lossy audio codec, specifically optimized for transparent
compression of stereo audio at bitrates of 160–180 kbit/s. Musepack and
Ogg Vorbis are rated as the two best available codecs for high-quality
lossy audio compression in many double-blind listening tests. Nevertheless, Musepack is even less popular than Ogg Vorbis and nowadays is used mainly by the audiophiles.
- flac – a lossless compression codec. This format is a lossless compression as like zip
but for audio. 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 recommended for archiving PCM files where quality is
important (e.g. broadcast or music use).
- aiff – the standard audio file format used by Apple. It is like a wav file for the Mac.
– 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.
- au – the standard audio file format used by Sun, Unix and Java. The audio in au files can be PCM or compressed with the μ-law, a-μlaw or G729 codecs.
Open file formats
– 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
- dct – A
variable codec format designed for dictation. It has dictation header
information and can be encrypted (often required by medical
- vox – the vox format most commonly uses the Dialogic ADPCM
(Adaptive Differential Pulse Code Modulation) codec. Similar to other
ADPCM formats, it compresses to 4-bits. Vox format files are similar to
wave files except that the vox files contain no information about the
file itself so the codec sample rate and number of channels must first
be specified in order to play a vox file.
- aac – the Advanced Audio Coding format is based on the MPEG2 and MPEG4 standards. aac files are usually ADTS or ADIF containers.
- mp4/m4a – MPEG-4 audio most often AAC but sometimes MP2/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.
- wma – the popular Windows Media Audio format owned by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection.
(.wav) – the older style Sony ATRAC format. It always has a .wav file
extension. To open these files simply install the ATRAC3 drivers.
- 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.
- dss – Digital Speech Standard files are an Olympus
proprietary format. It is a fairly old and poor codec. Prefer gsm or
mp3 where the recorder allows. It allows additional data to be held in
the file header.
- msv – a Sony proprietary format for Memory Stick compressed voice files.
- dvf – a Sony proprietary format for compressed voice files; commonly used by Sony dictation recorders.
- mp4 – A proprietary version of AAC in MP4 with Digital Rights Management developed by Apple for use in music downloaded from their iTunes Music Store.
– An iKlax Media proprietary format, the iKlax format is a multi-track
digital audio format allowing various actions on musical data, for
instance on mixing and volumes arrangements.