The strangely sermonic tone that this speech assumes is, I think, exactly the point.

演说中奇怪的布道式的语气，我认为，刚好切中要点。

youdao

The tone of the speech was upbeat.

这次讲话的语气颇为乐观。

《牛津词典》

You can use the pitch and tone of your voice to help emphasise descriptive sections of your speech, helping you create pictures in the minds of your audience.

你可以通过声调、语调的变化强调演讲中描述性的部分，帮助听众在脑海中勾勒画面。

youdao

Mr. Ahmadinejad's tone flip-flopped during the speech, appearing at times deliberately provocative and other times soft and eager to begin negotiations.

WSJ: U.S. Walks Out on Ahmadinejad U.N. Speech

And my question is, do you think that the tone, the -- at the Tucson speech he talked about civility and the idea that you can discuss your disagreements without anger and without this sort of poison that has marked so much in Washington.

WHITEHOUSE: Press Briefing

Despite this, the self-assured tone of Mr Brown's speech to Parliament is understandable.

ECONOMIST: Not so rosy | The