G2P or Grapheme-to-Phoneme conversion, is a technology that, given the selected language, converts an orthographic transcription into a phonetic representation of that word. In other words: it tells you how the word probably will sound when spoken. There is an International Phonetic Alphabet (IPA), created and mantained by the International Phonetic Association, that describes all the phonemes of all the human languages of the world.

IPA Kiel 2015Fig. 1: An overview of the IPA alphabetThe IPA, founded in 1897, uses a particular annotation to describes the huge variaty of sounds (see fig on the right).

To use this "symbols" in your text processor, one can download the IPA-fonts. However, the IPA-fonts are difficult to read and use. For a more practical use, the Speech Assessment Methods Phonetic Alphabet (SAMPA) was created. A computer-readable phonetic script using 7-bit printable ASCII characters, based on the International Phonetic Alphabet (IPA). A SAMPA transcription can be written in every (western) font, but Courier is preferred because it limits the confusion between (for example on this website)  /l/ and /I/ (In Courier it is /l/ and /I/).

Language dependency

The pronouncation of a word, depends of course from the language. The same orthographically written word, is pronounced differently in various languages.

For example, the capital of the Netherlands, Amsterdam, is transcribed as:

  • /'A m - s t @ r - d *A m/ in Dutch
  • /*E m - s t @ r - d 'E m/ in English
  • /*a m - s t @ r - d a m/ in Italian


There are a couple of issues when starting to align the transcriptions. The main issue are the "abbreviations": is the difference between the way a word is written and how it is pronounced by the majority of the native speakers.


Easy problems are words without a vowel: the are spelled out or "replaced" by the original word.

  • NCRV → /E n - s e - E r - v e/  (A Ducth broadcast organisation)
  • Mr → Mister → /M I s - t @ r/

If words contain one or more vowels, it depends on the local attitudes.

  • NOS →  N. O. S. → /E n - o - E s/ (the national Dutch broadcast organisation). NOS can be pronounced as nos /n O s/, but no one does it.
  • RAI→ /r Ai/ (the national Italian broadcast organisation). The word is perfectly pronouncable in Italian, so no one is using the spell-mode.

drmlkdrFig. 2: An example of the two pronouncations of dr in one streetname.A particular kind of abbreviations are those that depends of the context.

  • An appointment with dr. Corti → an appointment with doctor Corti
  • An appointment on the Corti dr. → an appointment on the Corti drive

A special kind of abbreviations are numbers. A normal number like 19 → sounds as nineteen → /n Ai n - t i n/. But numbers are context sensitive as well.

  • my phone number is 621888146 → 6 2 1 8 8 8 (or 3 times 8) 1 4 6
  • the cost in euro of that bridge is 621888146 → sixhundred twenty one million etc.

So, before using the G2P, one needs to preprocess the text in order to know what the most likely way of pronouncation will be.