Most AI voice output sounds flat for one reason that has nothing to do with the model: the script wasn't written for reading aloud. Text-to-speech engines read punctuation as timing instructions, not just grammar. Get the punctuation right and a decent voice sounds noticeably better. Get it wrong and even a good model sounds rushed or robotic. You can hear the difference yourself on the free voice generator.
The rules below apply whether you're narrating a YouTube video, giving a newsletter an audio edition or producing a podcast. Each comes with a short before-and-after you can steal.
Commas are pauses, not just grammar
A comma tells the model to breathe. Use one anywhere a human speaker naturally would, even if a strict grammar check would flag it as unnecessary. “Welcome back, to the show” reads more naturally aloud than the grammatically tidier version without the comma. The pause gives the listener a beat to register the greeting before the show name lands.
Keep sentences shorter than you think you need to
Long, clause-heavy sentences that read fine on a page often collapse into a run-on when spoken. If a sentence needs more than one comma to hold together, it's usually two sentences trying to be one. A useful ceiling is about 25 words; anything longer, read it aloud yourself and see where you run out of breath.
Full stops end a thought, not just a clause
Put a period where you'd naturally drop your pitch and pause when speaking, even if it produces shorter, choppier-looking text than you'd write for print. TTS engines commit to that drop every time. Inconsistent punctuation produces inconsistent, unnatural intonation.
Write numbers, symbols and names the way they're said
A voice has to guess how to say “3/4”, “$2.5M” or “Q3”, and it won't always guess the way you would. Spell out anything with more than one reading: “three quarters”, “two and a half million dollars”, “the third quarter”. Do the same for symbols like %, & and /.
For names and acronyms, listen once and respell anything the voice gets wrong: “Nguyen” might become “Win”, and an acronym you say as a word can be written as one. Fix the line, regenerate just that line, and move on.
Delete what only exists on a screen
“As you can see below”, “click here”, bullet points, image captions and parenthetical asides all assume a reader with eyes on the page. Turn lists into sentences, replace headers with spoken transitions (“Next, let's look at...”), and either cut asides or make them their own short sentence.
Give every speaker a clear line
In interviews, Q&A posts and co-hosted episodes, each voice should own whole sentences. Don't split one sentence across two speakers, and don't bury a quote inside narration with “she said” tags mid-line. Give the quote its own line and its own voice, and let the narrator introduce it in the sentence before.
Keep each speaker's lines in a consistent register, too. If the host is brisk and the guest is reflective, write them that way: short, punchy lines for one; longer, slower ones for the other. The contrast does more than any voice setting.
Read it aloud once before you generate
The fastest quality check costs nothing: read the script out loud yourself, at normal speed. Anywhere you stumble, run out of breath or lose the thread, the voice will too. Mark those spots, fix them, and then generate.
After generating, listen through once without stopping and note every line that sounds off. Then fix them in a batch. In Sintra Studio, regenerating a line you edited costs only that line's credits, and lines you didn't touch are free, so small fixes are cheap.
Three examples, one per format
A YouTube explainer line
The James Webb Space Telescope (JWST), launched 12/25/2021, observes primarily in the infrared (0.6–28.5 μm) — see the diagram above.
The James Webb Space Telescope launched on Christmas Day, twenty twenty-one. It sees mostly in infrared light, which is longer than anything our eyes can pick up.
The rewrite drops the acronym, the date format, the unit range and the reference to a diagram the viewer may not be looking at, and gives the visuals room to do their job. More on this in AI voiceover for YouTube creators.
A newsletter paragraph
This week: 3 things I learned shipping v2 (thread below 👇). TL;DR — ship smaller, talk to users, and don't over-engineer the onboarding flow.
This week, three things I learned shipping version two. The short version: ship smaller, talk to your users, and don't over-engineer onboarding. Let's take them one at a time.
The emoji, the “thread below” pointer and the abbreviations go; a spoken signpost tells the listener what's coming. If you write every week, see how to turn your newsletter into a podcast.
A podcast intro
Welcome to Episode #47 of The Build Log, the podcast about indie software where we discuss product, growth, pricing, hiring and everything in between with founders.
Welcome back, to The Build Log. This is episode forty-seven. Today, one founder, one pricing mistake, and what it cost them.
Short sentences, a comma for the greeting, the number written out, and a hook instead of a category list. Test an intro like this free, or see the AI podcast generator for full episodes.
Quick checklist before you generate
- Commas where a speaker would breathe.
- No sentence much over 25 words.
- Numbers, dates, symbols and units spelled out.
- Names and acronyms respelled if the voice trips on them.
- No “see below”, links, captions or emoji.
- A spoken intro and a clear closing line.
Test the actual line, not a sample
Generic demo scripts tell you how a voice sounds reading someone else's words. They don't tell you how it sounds reading yours. Test your own line free, no signup. It takes about fifteen seconds and settles the question a sample reel can't. And for a straight answer on where synthetic voice still loses to a human one, that's covered separately.