Learn Hardcore Russian: Иногда наш диалог переходит в шёпот, как будто мы сидим в библиотеке. - Sometimes our dialogue turns into a whisper, as if we were sitting in a library.

Breakdown of Иногда наш диалог переходит в шёпот, как будто мы сидим в библиотеке.

What is the nuance of наш диалог here? Could I just say наш разговор instead?

Both are possible, but they differ slightly:

диалог = dialogue, focuses on the exchange of lines between two (or more) people; it sounds a bit more bookish or formal, or stylistically “literary”.
разговор = conversation, talk, the most neutral, everyday word.
беседа = conversation, talk, but more polite, calm, often used for friendly, serious, or educational talks.

So:

Иногда наш диалог переходит в шёпот…
sounds like you’re describing the form of your interaction (like lines in a play or a script).
Иногда наш разговор переходит в шёпот…
sounds more everyday and colloquial, and is probably the most natural in casual speech.

All three are grammatically correct; the choice is mostly about style and nuance.

Why is it переходит в шёпот and not something like становится шёпотом?