When you first sign up, you'll have a fifty track download limit during your five day trial. Once your trial ends and your normal subscription begins, you'll have access to unlimited downloads.
If you'd like to gain immediate access to unlimited downloads, you can bypass your trial from your Billing page. To find that page, just click your profile icon at the top left of the screen, then Settings. On your Settings page, you'll see your Billing tab on the left.