Guides · 6 min read
Why text-to-speech skips or garbles equations, and what to do about it
A read-aloud tool speaks the characters stored in a file. An equation is usually stored as a picture, or as symbols whose meaning depends on where they sit on the page, so the voice goes silent or reads noise. The fix is to give the voice the equation's structure: a file with real maths markup, or a reader that rebuilds the structure before it speaks.
Updated 11 November 2026
What you hear, and why
| What you hear | What is in the file |
|---|---|
| Silence where the equation should be | The equation is an image. There is no text for the voice to read. |
| “x 2 plus y 2 equals r 2” | The powers are ordinary characters. That they were raised is layout, and layout is not in the text. |
| A fraction read as two separate lines, or with the bottom first | A PDF stores positioned characters, not an order. A formula is two-dimensional, so the order the voice picks is a guess. |
| “backslash frac open brace a close brace” | The voice is reading LaTeX source. Some PDFs made from LaTeX carry it as hidden text. |
| A symbol skipped or misnamed | The voice has no word for the symbol, or no rule for what it means here. |
None of this is a fault in the voice. A general reader is built for prose, where the characters in the file are the content. In an equation the structure is the content: what is over what, what is raised, what a sum runs over.
The problem is common enough to have its own support threads. On Microsoft's support forum, readers report Edge's Read Aloud skipping the equations in a maths textbook, and Zotero users describe read-aloud speaking invisible LaTeX source in arXiv PDFs.
Check your own file in a minute
- Open the PDF and try to select one equation with the cursor. If nothing can be selected, it is an image.
- If it can be selected, copy it and paste it into a plain text editor. What you see there is what a read-aloud tool is given.
- Compare it with the page. Missing powers, a fraction on one line with no bar, or symbols in the wrong order explain what you heard.
Four ways to get maths read properly
- Find a version with real maths markup. An EPUB or web page that uses MathML, or a page typeset with MathJax, carries each equation's structure, and assistive technology can read it. Publishers' HTML versions are often better than their PDFs.
- Use a maths-aware reading tool from your institution. Disability services often license tools that speak marked-up maths, such as EquatIO or ReadSpeaker. They work best when the source has MathML or LaTeX.
- Convert single equations yourself. If you have the LaTeX, the free LaTeX to speech converter turns it into words you can read, paste into notes or use as alt text.
- Use a reader that rebuilds the equations. Aethel reconstructs each printed equation from the PDF, scanned pages included, and reads it from its structure. That is the route for a whole textbook or paper that only exists as a PDF.
How an equation should sound
Read well, an equation is a sentence. Compare the printed formula with the words below it:
x = (−b ± √(b² − 4ac)) / 2a
Aethel says
x equals the quantity negative b plus or minus the square root of the quantity b squared minus 4 a c, over 2a
- Structure is spoken: “the quantity … all over 2 a” tells the listener where the fraction starts and ends.
- Symbols are named by meaning: ± is “plus or minus”, √ is “the square root of”.
- Subscripts, powers and functions have fixed words: “x sub i”, “x squared”, “f of x”.
The full list of conventions is in how equations are read aloud, and the LaTeX reference shows the spoken form of common commands.
What Aethel does with the same page
- Rebuilds each equation as structured maths when the book is imported, from text-based and scanned PDFs and from EPUBs.
- Reads the equation in words as part of the sentence, in the same voice as the prose around it.
- Keeps the printed equation on screen, typeset, and highlights the sentence being read.
- Describes figures and tables where the text refers to them, instead of reading stray labels.
You can hear the difference without an account: the equation demo plays ten well-known formulas, and the sample chapter shows a whole page being read.
Questions
Why does Edge, Adobe Reader or my phone skip equations when reading a PDF aloud?
They read the text layer of the PDF. An equation stored as an image has no text, and an equation stored as positioned characters has lost its structure, so it is skipped or read as loose symbols.
Can a screen reader read the equations in a PDF?
Only when the PDF was tagged with maths markup or each equation was given alternative text. Most textbook and paper PDFs have neither. HTML and EPUB versions with MathML are read far more reliably.
Is there a free way to hear an equation read properly?
For single equations, yes: paste the LaTeX into the LaTeX to speech converter. For whole books, Aethel's free trial covers five books and an hour of narration, with no card.
Does Aethel read every equation correctly?
It reads standard notation from algebra to vector calculus, probability and linear algebra. Unusual or badly printed notation can still go wrong, which is why the printed equation always stays on screen next to the words.