Metaphone

Metaphone is a phonetic algorithm designed to index words based on their approximate English pronunciation.

It generates an alphanumeric key that essentially represents the consonant sounds of a word, making it easier to (fuzzy) search terms that sound similar, even when misspelled.

The Metaphone algorithm applies a series of phonetic transformation rules to convert a word into a simplified representation of its pronunciation. These rules include:

— Normalizing similar sounds: C and Q are coded as K

— Handling special cases: G before E, I, Y is coded as J

— Removing letters that are traditionally silent in English

— Ignoring vowels in the middle of words

Given a Metaphone key, there is no inverse algorithm that allows direct retrieval of a word.

To search for a word, compare the desired Metaphone key to the key of each entry in a dictionary or database. Words with matching or similar keys are considered phonetically similar.

Metaphone has limitations due to its reliance on English phonology.

The algorithm becomes less reliable for words from other languages, proper nouns, or regional pronunciation variations.

Its aggressive vowel simplification can also lead to significant collisions between words that are otherwise phonetically distinct.

A Metaphone key is an alphanumeric string primarily composed of the 16 characters 0BFHJKLMNPRSTWXY and sometimes the vowels AEIOU, but only at the beginning of the key to represent the initial sound of a word.

The key length is variable, generally from 1 to 8 characters (sometimes more for very long words).

The key contains no digits other than 0.

An evolution of the algorithm, called Double Metaphone, was proposed in 2000. This version generates two keys simultaneously to better handle pronunciation variations and improve coverage of words of non-English origin.

Another version, Metaphone 3, offers further refinement of the phonetic rules to reduce ambiguities.

Metaphone was published in 1990 by Lawrence Philips as part of work to improve previous phonetic methods such as Soundex.