French text to speech: reading fractions aloud
1/2, 3/4, 2/3, half, one and a half: a fraction written cleanly has exactly one spoken form, yet a synthetic voice can get it wrong in six different ways. The table of forms that stumble, and how to write them so they read right.
A fraction is a place where writing and speech part ways completely. In French, "1/2" is never said "un slash deux" or "un sur deux" when it means a quantity: it is said "un demi" (a half). "3/4" is "trois quarts" (three quarters), "2/3" is "deux tiers" (two thirds), and the glyph "½" contains no word you can read left to right. Nothing in these strings of characters tells a machine how to pronounce them. A synthetic voice with no dedicated rule does what it knows how to do with digits and a symbol: it reads them one by one, and "a recipe for 1/2 litre" becomes "un slash deux litre", which the ear catches at once as a mistake.
The table of forms that trip up the voice
| Written form | Expected reading (French) | Common error |
|---|---|---|
| 1/2 | un demi | "un slash deux", "un sur deux", "un divisé par deux" |
| 1/4 | un quart | "un slash quatre", "un quatrième" |
| 3/4 | trois quarts | "trois slash quatre", "trois sur quatre" |
| 2/3 | deux tiers | "deux slash trois", "deux troisièmes" |
| 5/8 | cinq huitièmes | "cinq slash huit", "cinq sur huit" |
| ½ | un demi | (glyph ignored, or read as bare "un") |
| ¾ | trois quarts | (glyph ignored) |
| 3 1/2 | trois et demi | "trois un slash deux", "trois espace un demi" |
| 1 h 1/2 | une heure et demie | "une heure un slash deux" |
| 1/10 | un dixième | "un slash dix", "un sur dix" |
Each row is a test you can run in two minutes against any tool, ours included. The right-hand column is not a caricature: these are the readings you actually hear from generic voices that predict the sound with no model of what the text means.
Why this is harder than a whole number
A whole number has a single, predictable reading: "42" is "quarante-deux" everywhere, always. A fraction is not like that. First, three spellings coexist for the same value: the slash form ("3/4"), the composed glyph ("¾"), and sometimes the form already written out in words. Second, the slash itself is ambiguous: in "3/4" it means "quarters", in "km/h" it means "per", in "and/or" it is not read at all. Same character, three jobs. Third, French makes agreements the digits do not show: "un demi" but "une heure et demie", "trois quarts" with an s that the "3/4" spelling never displays. So the voice has to recognise that this is a fraction, choose the right word, then inflect it.
That is the whole logic of the French text to speech page: what matters happens before any sound comes out, in how the text is recognised and rewritten for the voice. A beautiful voice that is poorly prepared will say "un slash deux" without blinking; an average voice that is well prepared will say "un demi". The work is not in the timbre, it is in reading the patterns, exactly as with reading numbers aloud and with number ranges.
What WeDispatch does about it, without over-promising
Everyday fractions (halves, thirds, quarters, and their glyph forms) are handled by the normalisation applied to every article. That is the baseline, and it covers the vast majority of what you meet in a real text: a recipe, a proportion, a duration.
What remains are the cases where even a human hesitates. "1/3" is "un tiers" in a recipe, but "un sur trois" in "une chance sur trois" (a one-in-three chance): there the slash expresses a ratio, not a part, and the reading changes. No rule can reliably guess the intent behind the slash, and claiming otherwise would be dishonest. For a form that recurs across all your content and must always be said a certain way, the pronunciation lexicon lets you declare the expected reading once, with nothing to regenerate.
The writing habit that fixes almost everything
The safest form is also the most readable on the page: write the fraction out in words when it is simple. "Un demi-litre" rather than "1/2 litre", "les trois quarts des lecteurs" rather than "les 3/4 des lecteurs", "une heure et demie" rather than "1 h 1/2". The text gains in clarity for the eye, and the audio becomes correct as a by-product, with no setting to tweak. Keep the numeric notation for the places where it truly earns its keep, a technical table for instance, and check those places by ear before publishing. This is not a constraint imposed by audio: it is good writing, and a listen-through before publishing catches the rest.
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