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Sound File Types

Sound or Audio File Formats

 
There are several  types of Audio files. The most common are Wave files (wav) and MPEG Layer-3 files (mp3).

The type is indicated by the file extension (what comes after the "." in the file name). For example, ".wav" or ".mp3"

Sound energy is changed into electrical energy and the voltage variations of the signal are then converted into a code that can be read by a computer.

How audio is compressed and stored is call the codec and that determines how small the file size is and how good the quality of reproduction will be. Some file types always use a particular codec. For example, ".mp3" files always use the "MPEG Layer-3" codec. Other files like ".wav" and ".dct" files support selectable codecs. For example, a ".wav" file can be encoded with the "PCM", "GSM6.10", "MPEG3" and many other codecs. Be careful not to confuse the file type with the codec - it often surprises people to know you can have a "MPEG Layer-3" encoded ".wav" file.

Some file types just contain the audio information. But other file types can contain additional header information which can contain other information about the file (eg .dct files have information about the sender, priority, notes and other data in the file itself).

There is a lot of specialist software designed to deal with sound files. For the DiDA we are only going to use sound formats that can be imported into Flash.

See Flash Sounds

List of Audio File Format Types

Open File Formats
  • wav - standard audio file 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 10MB per minute of music. Wave files can also be encoded with a variety of codecs to reduce the file size (for example the GSM or mp3 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 good for music storage but it 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 not as common.
  • 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. Wav files can also be encoded with the gsm codec.
  • dct - A variable codec format designed for dictation. It has dictation header information and can be encrypted (often required by medical confidentiality laws).
  • flac - a lossless compression codec. You can think of 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).
  • au - the standard audio file format used by Sun, Unix and Java. The audio in au files can be PCM or compressed with the ulaw, alaw or G729 codecs. 
  • aiff - the standard audio file format used by Apple. It is like a wav file for the Mac. Sample .aif file.
  • 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. Vox a very old file type and is pretty poor.
  • 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.
Proprietary Formats
  • wma - the popular Windows Media Audio format owned by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection. 
  • 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. 
  • atrac (.wav) - the older style Sony ATRAC format. It always has a .wav file extension. To open these files simply install theATRAC3 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.
  • msv - a Sony proprietary format for Memory Stick compressed voice files. You might need a Sony plugin to load this. Click here.
  • dvf - a Sony proprietary format for compressed voice files; commonly used by Sony dictation recorders. You might need a Sony plugin to load this. Click here.

Other Formats

  • atrac (.oma, .omg, .atp) - the newer style Sony proprietary format designed for minidisc use. It always has a .oma, .omg or .atp file extension. It is similar to mp3 and probably only useful if you are reading files from minidiscs or writing for minidiscs. Note most of these files are rights managed so you cannot open them in any software programs.
  • mid - the midi file is not an audio file format at all. It is just a list of musical notes which a synthesizer can play.
  • ape - the file format from Monkey's Audio is claimed to give about 50% compression without loss in audio quality.

This information was extracted from http://www.nch.com.au on 31/10/10