(as) clear as a bell
1. Very crisply audible; very easy to hear. Unfortunately, our next-door neighbors fight a lot, and we can hear them clear as a bell—even at 3 AM! With these new headphones, you'll be able to hear music as clear as a bell.
2. Easy to understand; very clear. These directions are as clear as a bell, so you shouldn't have any questions.
as clear (or sound) as a bell
perfectly clear (or sound). 1993 Independent We spent a few thousand on redecoration, but basically the place was sound as a bell.