Custom Startup Sounds Cut Off

I like to make my own startup sounds for Windows. They
are all in .Wav format (standard PCM format). However,
some of the files I play at startup don't fully play.
They are cut off at random times. I've noticed that the
smaller files play fully.

I was wondering if there was a limit placed on the size
or length of the song played at startup, and if there
was, is there some way that I can change it in order to
play the full song. Thanks!

*Note: Full song does NOT mean a 3 minute long wav
file. The largest file I have is a little over 6 MB.