Another aspect that we should talk about is that many audio systems have more than one output. By sending different audio signals to separate outputs (called channels), it is possible to produce the illusion of directionality and space. The number of channels on these systems can vary from one (mono) or two (stereo), to several more on surround sound systems.
The PCM format described earlier can store audio for multiple channels at once, by interleaving one sample from each channel in the correct order. The following figure shows an example of this for a stereo system:
Besides volume and pitch, which we have examined earlier, there is another property that you will usually find in every audio library, called panning. Panning applies to stereo systems, and allows you to simulate the position of the sound, placing it anywhere between the left and the right channels. For positioning in configurations with more than two channels, you normally use other advanced features, such as 3D sound.