In Poe's celebrated short story "The Tell-Tale Heart," the unnamed narrator attempts to convince the audience of his sanity as he elaborates on his brutal crime. In the first paragraph of the story, the narrator comes across as manic when he shouts, repeats himself several times, speaks in fragmented sentences, and attempts to describe his supernatural sense of hearing. The narrator is also determined to prove his sanity, which contributes to his defensive, agitated tone. He believes that his audience is doubting him, and he is determined to prove them wrong. The narrator ends the first paragraph by stating that he will prove his sanity by calmly telling the story of how he murdered the old man. The narrator's claim is ironic, because he is anything but composed.

As the story develops, the narrator continues to speak in an anxious, uneasy tone, which highlights his mental instability and contributes to the unsettling mood of the narrative. The short, abrupt sentences reveal the narrator's troubled mindset, and the ominous diction emphasizes his insanity. The audience associates words like "madness," "haunted," "evil," and "darkness" with the narrator's disturbed psyche and finds the description of his crime particularly unsettling. Throughout the story, the narrator continually attempts to persuade the reader that he is a rational, sane person, which also creates a desperate, pleading tone. Towards the end of the story, the narrator elaborates on his interaction with the police officers in a frantic tone by saying,

Oh God! what could I do? I foamed—I raved—I swore! I swung the chair upon which I had been sitting, and grated it upon the boards, but the noise arose over all and continually increased. It grew louder—louder—louder! And still the men chatted pleasantly, and smiled. Was it possible they heard not? Almighty God!—no, no! They heard!—they suspected!—they knew!—they were making a mockery of my horror!—this I thought, and this I think. (Poe, 8)

Overall, the unreliable narrator of Poe's classic short story "The Tell-Tale Heart" utilizes a defensive, agitated tone and gives the impression that he is a desperate, mentally insane individual.

The narrator believes his tone to be persuasive and calm, as he is trying to convince someone that he is not crazy. In the first line, he asks,

True!—nervous—very, very dreadfully nervous I had been and am; but why will you say that I am mad? The disease had sharpened my senses—not destroyed—not dulled them.

He describes how perceptive his senses have become, especially his hearing, saying, "I heard all things in the heaven and in the earth. I heard many things in hell. How, then, am I mad?" He believes that this acuteness of his senses is evidence of how healthy he is, and he believes that he can tell his story "calmly." However, the fact that he believes he can hear what's happening in heaven and hell, and even everything on the earth itself, is pretty crazy-sounding, and the sheer number of exclamation points used in the story—forty-three—makes it seem as though "calm" is not exactly the right word to describe his tone!

Instead, the narrator's tone is somewhat aggressive, excitable, and even manic. His many, many references to his auditor make him sound aggressive, especially in the first three paragraphs, where he addresses "you" seven times. His mania and aggression are both apparent in the third paragraph, which begins,

Now this is the point. You fancy me mad. Madmen know nothing. But you should have seen me. You should have seen how wisely I proceeded—with what caution—with what foresight—with what dissimulation I went to work!

In these lines, he is obviously trying to sound convincing, addressing his auditor directly three times, though this makes him sound aggressive. The abbreviated structure of the first three sentences also makes him seem manic. He is very excitable.

The narrator’s tone is arrogant and excited.  He is excitable because he is mentally unstable.  Yet he is arrogant enough to believe he is right.

The narrator in “The Tell-tale Heart” is an unreliable narrator.  We realize from his tone that he is mad.  The narrator is obsessive and paranoid. He describes the killing of his roommate and the consequences in a matter-of-fact way, but in a very excited way.

The narrator goes to great lengths to prove that he is not mad, but almost everything he says confirms that he is not in his right mind.  He tells us that he had nothing at all against the old man.

It is impossible to say how first the idea entered my brain; but once conceived, it haunted me day and night.  Object there was none. Passion there was none. (enotes etext p. 4)

Yet the old man has to die!  The narrator explains that it is because he has an evil eye.  We can’t let that stand!

Oh, you would have laughed to see how cunningly I thrust it in! I moved it slowly—very, very slowly, so that I might not disturb the old man's sleep. It took me an hour to place my whole head within the opening so far that I could see him as he lay upon his bed. (p. 4)

The narrator painstakingly describes how it took him an hour to stick his head in the door.  He is thoroughly excited.  An example of this tone is the use of exclamation points and words like “Ha!” with short, choppy sentences. 

The tone of the story is a choice made by Poe to ensure that his narrator seems mad, but nearly lucid.  The narrator is obsessed and excitable, but there is enough normalcy there that it makes the ending more believable.  We realize that this man could hold a conversation with the police without arousing suspicion for only a short time, and he would not realize it when they began to suspect him because he is so arrogant.

The tone also adds to the suspense, because we know that this arrogant and excitable man is up to something.  Early on we are told that he killed the man, and the tone makes us interested in learning how.

The narrator's tone in this story is quite overwrought, leading to a climax at the end when he shrieks out his confession to murder. He is disturbed in his mind, and this is conveyed in his nervous agitated manner. He often gives way to exclamations, although he also tries to speak quite rationally and logically. He also addresses the reader directly on several occasions, creating the sense of a more intimate and close audience. This psychologically intense tone conveyed through first-person narrative is common to several of Poe's short stories like 'The Black Cat' and 'Berenice', which also feature acts of murder and mutilation by obviously psychologically-disturbed individuals.