Why is all my music slightly too slow?

I can't believe I haven't seen more posts about this. Since the latest iTunes update, any and all of my music on my laptop has been playing about half a second too slow. This has been going on since July 26th and I'm dead tired of it. I didn't get all of this music which cost me hundreds of dollars to be ruined for no reason. I plugged my phone into my computer and now all the music on there is slow, and when I play tracks from my laptop against the same track on YouTube, the YouTube one within a few seconds passes the mp3 from my laptop. What am I supposed to do now? Just try to ignore such an irritating and distracting issue?