QuickTime 4 Reference

Mapping Numerical Sample Values with Four Parameters

A device performing audio A/D or D/A conversion must map numerical sample values to voltage levels at its electrical jack in some deterministic way. Similarly, a program that displays an audio waveform on screen must map numerical sample values to screen Y-coordinates in some deterministic way. This section discusses the cases where the numerical sample values are linearly-related to the voltage levels or Y-coordinates. Other cases, including compression or companding, then follow trivially.

All possible linear mappings between numerical sample value and voltage or Y-coordinates can be represented with two parameters (i.e., two degrees of freedom). It is more convenient and more common, however, to represent the mappings with four parameters, as explained in the next section.

The A/D - D/A Example

A Waveform Example