Wikipedia
DirectSound is a deprecated software component of the Microsoft DirectX library for the Windows operating system. DirectSound provides a low-latency interface to sound card drivers written for Windows 95 through Windows XP and can handle the mixing and recording of multiple audio streams.
Besides providing the essential service of passing audio data to the sound card, DirectSound provides other essential capabilities such as recording and mixing sound, adding effects to sound (e.g., reverb, echo, or flange), using hardware accelerated buffers in Windows 95 through XP, and positioning sounds in 3D space. DirectSound also provides a means to capture sounds from a microphone or other input and controlling capture effects during audio capture.
After many years of development, today DirectSound is a mature API, and supplies many other useful capabilities, such as the ability to play multichannel sounds at high resolution. While DirectSound was designed to be used by games, today it is used to play audio in a large number of audio applications. DirectShow uses DirectSound's hardware audio acceleration capabilities if the sound card's hardware audio acceleration capabilities exist and are exposed by the audio driver.