Direct Sound

Direct Sound is a Windows audio interface introduced in Win98.

One of the reasons was to Improve the gaming experience as Wave Out was a bit to slow.

From Windows 10 on it is depreciated in favour of WASAPI in shared mode.

 

Like all operating systems, Windows is build with multiple audio streams in mind.
You are watching a video and want to hear a notification when a email comes in.
This can only be done it the audio of both streams are mixed.
You can only mix audio digital if both have the same sample rate.
This is what Direct Sound does for you.
All audio is send to the audio engine where it is resampled (if needed), converted to 32 bit float, mixed, dithered and converted back to integer.
This according to the settings in the audio panel.

 

Because of this the audio is no longer bit perfect by design.
That is inherent to dither and re-sampling but should we care?

This is covered in detail in Windows Sample Rate Conversion.