Sample rate conversion
 What is sample rate conversion?
Most sound cards can only work on a single sample rate (48kHz typically). But real audio files may have different rates. Thus, sample rate conversion must be done.
In most cases it is done by Windows automatically. But some restrictions are appied for such automatic conversion algorithm. It must be fast and have low latency. Quality is only at the third place. Because of this, third-party sample rate conversion is required for the best conversion quality.