Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
To start with, I need to know the version of mac osx you have on your machine, you can check as follows.Click the apple sign at the top left of your screen, then click about this mac. And then where it says version, send that to me as a reply.
Also, if you could describe your recording process, what you are using for inputs, any special equipment, etc..
That would be helpful, thank you.
To begin to try and answer that, I need to know the version of Garage band you are using, and also the version of mac osx, and also how you are receiving the input for your tracks.
Please provide as much detail as possible, thank you.