Why is WASAPI so much slower than ASIO?

Question

I measured the round-trip latency of RtAudio Duplex Mode example by an oscillograph. The result on the average as blow,

ASIO 15ms

WASAPI 50ms

Why is WASAPI so much slower? All documents on the Internet says them have the same performance.

OS: Windows 7 Ultimate

Compiler: VC2013

Answer 1

One reason is that you're using Windows 7. Give Windows 10 a try; this has some latency improvements