How to fix quality of iTunes downloaded music...

How do I ensure the quality of music I am downloading from iTunes is cd or better?

When you download music from the iTunes Store, it is encoded in AAC/256, which is very good for most purposes, but is less than CD quality. There is no way to upgrade it to CD quality.

To get CD quality, you can rip from CD or purchase from an online store that sells lossless downloads.

I've noticed some music I downloaded sounds awful.

If a track simply does not have acceptable audio quality, contactiTunes Customer Service for a refund.