7 mistakes that make an AI voice sound robotic (and fixes)
12 October 2026 · 7 min read
A "robotic" AI voice is rarely the engine's fault. Nine times out of ten the text was badly prepared: the voice reads exactly what it is given, without guessing where you would have breathed. Here are the seven mistakes we see most often in texts submitted to Aievalu, each with a before/after example and the fix, from the most common to the most insidious.
1. The wall of text with no punctuation
A six-line paragraph with a single comma produces one long, flat breath that speeds up towards the end. The engine does not know where your ideas are, so it just keeps going. Punctuation is your only directing tool, and the full stop is your best friend.
| Before | Today we're going to see how to edit a video quickly without complicated software and I'll show you the three settings that change everything from the very first export |
|---|---|
| After | Today, we're going to see how to edit a video quickly, without complicated software. I'll show you three settings. They change everything, from the very first export. |
Simple rule: one idea per sentence, a full stop every fifteen to twenty words. A comma gives a short pause, a full stop a clean one, an ellipsis a hesitation. If you write for the ear, read your text aloud before pasting it.
2. Numbers written in the wrong form
"1500" will be read "fifteen hundred" or "one thousand five hundred" depending on the voice; "2026" as a year is fine, "2026" as a quantity is not. Trouble starts with amounts and decimals: "£9.99" glued to the number, "3,5" with a European comma, a phone number in one block.
| Before | The pack costs €9 for 100000 characters i.e. €0.09/min |
|---|---|
| After | The pack costs nine euros for 100,000 characters, about nine cents a minute. |
When a figure matters, write it the way you would say it. Units in full words ("euros", "minutes", "per cent") avoid surprises, and a phone number is dictated in pairs separated by full stops. The text-to-speech guide covers dates, times and percentages in detail.
3. Acronyms left as they are
"NHS" will be spelled out, "NASA" said as a word, "AI" sometimes read as "eye". The engine chooses, not you. Even our own brand name is read differently depending on how it is written.
| Before | GDPR and the AI Act require a notice on AI-generated content. |
|---|---|
| After | G.D.P.R. and the A.I. Act require a notice on content generated by artificial intelligence. |
For an acronym that is spelled out, separate the letters with full stops. For one that is pronounced as a word, write it as a word, lower case if needed ("nasa"). For a rare technical term, write it phonetically in the text sent to the engine, even if the spelling shown on screen stays correct.
4. Missing commas around asides
"Marie who comes from Lyon arrives tomorrow" and "Marie, who comes from Lyon, arrives tomorrow" do not sound the same. Without the commas, the voice glues the aside to the subject and the meaning blurs. It is the quietest mistake, and the one that makes people say "you can tell it's a machine".
| Before | This setting which everyone forgets saves ten minutes per video. |
|---|---|
| After | This setting, which everyone forgets, saves ten minutes per video. |
Bracket asides, appositions and displaced clauses. Every added comma becomes a micro-pause, and those micro-pauses are what gives the impression of a reader who understands what they are reading.
5. The wrong tone for the content
A cheerful voice on a tax tutorial, a neutral voice on a TikTok teaser: the text is fine, the voice is fine, the match is wrong. Aievalu voices come in several tones (Marie in French: neutral, excited, happy; Paul in American English: neutral, cheerful, confident) precisely for this.
Listen to the same sample in each tone on the voices page before choosing. For short formats, the AI voice for TikTok and Reels guide explains why the energy has to be in the first three seconds; for a course, neutral narration tires the listener less across twenty modules.
6. Sentences that run too long
Beyond twenty-five words, even a human voice runs out of air. Synthesis never takes a breath: the sentence flattens and the ending becomes inaudible. Cascading subordinate clauses ("which", "whose", "because", "while") are the warning sign.
| Before | If you want your video to be watched to the end while attention drops after thirty seconds because people scroll, you need a hook. |
|---|---|
| After | Attention drops after thirty seconds. People scroll. If you want to be watched to the end, you need a hook. |
Cut. A short sentence, a medium one, a short one: that three-beat rhythm reads well to the ear. Remember that one Aievalu generation takes 1,500 characters, about ninety seconds: a passage can be fully re-read in less time than it takes to regenerate it.
7. Publishing without listening
The last mistake is not in the text. An odd liaison, a misread proper noun, an intonation that falls: it is audible in ten seconds and fixed in thirty. Too many videos go out with a reading error the author would have caught by listening once.
The method that works: listen to the whole clip, note the sentence that jars, rephrase it (a comma, a moved word, a spelled-out acronym), then regenerate only that passage. With per-character billing, redoing one sentence costs a few cents, not a monthly credit; the FAQ on character counting explains how characters are counted and why a technical failure is refunded.
The two-minute test
Take one paragraph of your next script. Apply the seven points: punctuation, numbers, acronyms, asides, tone, length, listening. Paste it into the free trial on the home page and compare with the raw version. The difference is usually clearer than switching tools, which our round-up of the best AI voice generators confirms: on equal text, recent engines are close; on well-prepared text, all of them sound better. If you write for a channel, the YouTube voice-over guide walks through these rules in editing order, and the pricing page shows the real cost of a retake.