Sound - Digital Audio File Formats

[under construction - more information coming soon]

Uncompressed

Standard for uncompressed CD-Quality audio on Windows systems, which uses PCM format recording. A CD-quality recording has a sample rate of 44.1kHz at 16 bit resolution.
- File size: approx 10.1Mb per minute. This figure is the same for all WAV files at CD quality, as file size is only related to file length, not to the audio content of the file. The figure is reached by the following calculation;
  2 channels [stereophonic] * 16 bits * 44100 samples per second * 60 seconds = 84672000 bits = 10 584 000 bytes = 10.1 Mb

Used in portable audio recorders and digital audio workstations for broadcast use.

Compressed sound file format, developed by the Motion Picture Expert Group (MPEG) as part of their MPEG1 video standard, and later extended to MPEG2 Layer 3 standard.
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.
There are 2 parameters that can be adjusted to vary the quality and size of the MP3 file.
- Bit Rate
- Sample Frequency
Examples of MP3 compression 1m10s excerpt from Symphony No.3 by Camille Saint-Saëns
- CD quality WAV (11.7Mb) [uncompressed PCM audio - Windows]
- CD quality AIFF (11.7Mb) [uncompressed PCM audio - Apple]
- 320kb/s constant bitrate (2.67Mb) [compressed MP3]
- 128kb/s constant bitrate (1.07Mb) [compressed MP3]
- 64kb/s constant bitrate (548kb) [compressed MP3]
- 32kb/s constant bitrate (274kb) [compressed MP3]
- 16kb/s constant bitrate (137kb) [compressed MP3]
- 8kb/s constant bitrate (69kb) [compressed MP3]
More information

A proprietary version of AAC in MP4 with Digital Rights Management developed by Apple for use in music downloaded from their iTunes Music Store.