I will defer to the musicians with more experience handling audio files than I, but you shouldn't have to pay for a basic MP3 converter. My favorite is Goldwave (
www.goldwave.com), developed by some folks out of Canada. There's a free downloadable version that should handle all your conversion needs, and a full version that is unlockable with a payment ($50 when I paid for it). It's excellent. Easy to use, lots of functionality, does a remarkable job of getting rid of background noise and hiss, making it ideal for converting files from vinyl. I love it.