Learn Italian: Il suono è più incomprensibile di quello che credevo. - The sound is more incomprehensible than what I believed.

When you compare something to a whole clause (a phrase with a conjugated verb, like "what I believed"), you can't just use a simple di or che. Instead, you have to use a phrase like di quello che or di quanto. Literally, it translates to "than that which".

I thought we needed the subjunctive for this type of comparison. Why is it credevo (indicative)?

Good catch! If we had used di quanto instead, it would trigger the subjunctive: di quanto credessi. But di quello che is more conversational and generally takes the normal indicative mood (credevo). Both phrases mean the exact same thing.

Could I use pensavo instead of credevo in this sentence?

Yes, absolutely. In contexts like this where you are expressing a past opinion or expectation, credere (to believe) and pensare (to think) are completely interchangeable. Saying di quello che pensavo is perfectly natural here.

How does the word incomprensibile break down?