Phonetic Normalization

Phonetic normalization is a form of Text Normalization done for Information Retrieval applications


  • in English (and many other languages) words that are pronounced the same way can be spelled differently
  • some IR applications need to account for that
  • use phonetic normalization to reduce similar-sounding words to the same token

So, phonetic normalization algorithm should:

  • facilitate the retrieval of words with similar sound.


Soundex is a phonetic normalization algorithm

  • encodes words according to their pronunciation
  • each word is compressed into a 4 characters code: Soundex code.


  • keep the first letter of the name
  • drop all a, e, i, o, u, y, h, w.
  • replace similar-sounding ("phonetically clone") consonants with digits:
    • bfpv -> 1;
    • cgjkqsxz -> 2;
    • dt -> 3;
    • l -> 4;
    • mn -> 5;
    • r -> 6;
  • now remove all consequent occurrences of the same digit
  • keep only first four characters of the resulting string (append with zeros if needed)


  • Herman -> H655
  • Veronika, Veronique -> V652


Useful for

  • First and last names
  • Street names
  • etc