PCM

Overview

The term "PCM" stands for "Pulse Code Modulation" and refers one system for encoding digital audio after AD conversion.

Basics

There are different types of encoding that can be used for digital audio, depending on the application and quality requirements. For example; professional audio requires the highest quality attainable as versus telephone communication which can employ much lower quality audio and still be acceptable for speech. One other consideration is the ease with which the digital audio signal can be processed; which in pro audio applications is important for processing such as level adjustment, equalization (or “tone” adjustment), and mixing. These considerations were part of the reason why PCM encoding was adopted by SONY and Phillips for the format of the encoding in the original Compact Disc (CD) standard. Computer file formats such as WAVE and AIF also utilize the PCM format for similar reasons; and most computer audio software is designed to use one of these formats as its “working” file format. The fundamental idea is similar to a “graph” of a waveform; where there are evenly-spaced divisions on the horizontal “X” axis that represent time, and evenly spaced divisions on the vertical “Y” axis that represent amplitude. Each time division represents one “cycle” at the sample frequency.