What are the best working music-files?

[Sigtrygg]

Hello!

At the moment I make a christmas-klick-and-see-what-happen-picture
and I have the following problem:

When I use music in form of midi the velocity of moving sprites decreases
much. When I use mp3-music velocity decreases less.

So my question is what kind of music-file is the best according holding
the speed of game high?

Have a nice weekend!

Sigtrygg