Windows audio

You can find tons of complains about XP sound quality on the internet.
The K-mixer is the culprit.
The mixing and sample rate conversion is done in integer.
Probably one of the design goals was to be as frugal on system resources as possible as the hardware at that time (1999) didn't had the power of today's PCs.
Despite all these complains, it is possible to get bit perfect output from XP.
The trick is to avoid that the K-mixer kicks in and have unity gain.
In this case XP delivers bit perfect output.
Microsoft dropped support, XP is no longer maintained.


From Vista on Windows has a redesigned audio stack.
The DSP (Digital Signal Processing like sample rate conversion, mixing, etc.) is done in 32 bits float.

Windows Vista features a completely re-written audio stack designed to provide low-latency 32-bit floating point audio, higher-quality digital signal processing, bit-for-bit sample level accuracy, up to 144dB of dynamic range.

 

Source: Wikipedia

 

The architecture is completely different. Regardless of the number of streams, every stream is converted to float and back to integer and dithered.
As the mixer is always active, you can’t get bit perfect output out of the box.
You need media players supporting drivers like ASIO or Microsoft own WASAPI to do so.

 

Later versions of Windows use by and large the same audio stack.
As far as I know, no major revisions but this is no surprise as audio has a low priority at Microsoft.