The IDirectSoundBuffer interface enables your application to work with buffers of audio data. Audio data resides in a DirectSound buffer. Your application creates DirectSound buffers for each sound or audio stream to be played.
The primary sound buffer represents the actual audio samples output to the sound device. These samples can be a single audio stream or the result of mixing several audio streams. The audio data in a primary sound buffer is typically not accessed directly by applications. However, the primary buffer can be used for control purposes, such as setting the output volume or wave format.
Secondary sound buffers represent a single output stream or sound. Your application can play these buffers into the primary sound buffer. Secondary sound buffers that play concurrently are mixed into the primary buffer, which is then sent to the sound device.