Pulse Code Modulation (PCM) is the process most often used to transmit and store uncompressed digital audio data. Most uncompressed digital audio file formats--including WAV, AIFF, and CDDA--use PCM as the format for the audio data. PCM is not new technology; it was developed in 1937 by British engineer Alec Reeves while working for International Telephone and Telegraph.3.2
When an analog-to-digital converter translates analog audio samples into binary ``words,'' it uses PCM to transmit the individual bits of the words as voltages (``1'' as a positive voltage; ``0'' as the absence of voltage), which can then be reconstituted as binary data for storage in a computer file or on a compact disc. PCM is the audio equivalent of ASCII text; because of its simplicity, most audio programs can play PCM.3.3 It can accommodate a number of different resolutions (8-, 16-, and 24-bit depths are common), sampling rates (usually between 22 kHz and 96 kHz), and channel configurations (for example, mono, stereo, and 5.1 surround sound).