Learn Italian: La smentita non ha diminuito il clamore. - The denial did not reduce the uproar.

Diminuire (to decrease/reduce) can take either auxiliary depending on how it's used. Here, it is used transitively—it has a direct object (il clamore). When someone or something reduces something else, you use avere. If it were used intransitively (meaning the subject itself decreased), you would use essere, for example: Il clamore è diminuito (The uproar decreased).

How is the word smentita (denial) formed?

It comes from the verb smentire (to deny, refute, or retract). If you look closely, you'll see the verb mentire (to lie) with the prefix s-, which often acts as a reverser or negator in Italian. So, a smentita is effectively the act of declaring a previous statement to be a lie.

How would I add "As far as I know" to this sentence using a limitative clause?

You can use Per quanto ne so (using the indicative mood) or Per quanto io sappia (using the subjunctive mood). Added to the sentence, it becomes: Per quanto ne so, la smentita non ha diminuito il clamore. The subjunctive version sounds slightly more formal or implies a bit more doubt, but both perfectly restrict the statement's validity to your personal knowledge.

Could I use rumore instead of clamore for "uproar"?