Bo SN

Hi, Whenever I speed up or slow down the bpm in a music track in Mixpad, the sound gets "muffled" and "weak". When I used Mixpad in MAC OSX on my old laptop I didn't experience this problem. But now I have a new laptop with Windows I experience this problem every time, meaning I can't pitch the bpm in tracks up or down when I make a mixtape (dance/house music). Why is that, and how do I fix it? Thanks Bo