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This article is about the phonetic algorithm. For the Rock n' Soul band, see the SoundEx.

Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling.[1] The algorithm mainly encodes consonants; a vowel will not be encoded unless it is the first letter. Soundex is the most widely known of all phonetic algorithms (in part because it is a standard feature of popular database software such as DB2, PostgreSQL,[2] MySQL,[3] Ingres, MS SQL Server[4] and Oracle[5]) and is often used (incorrectly) as a synonym for "phonetic algorithm".[citation needed] Improvements to Soundex are the basis for many modern phonetic algorithms.[6]


Soundex was developed by Robert C. Russell and Margaret King[7] Odell and patented in 1918[8] and 1922.[9] A variation called American Soundex was used in the 1930s for a retrospective analysis of the US censuses from 1890 through 1920. The Soundex code came to prominence in the 1960s when it was the subject of several articles in the Communications and Journal of the Association for Computing Machinery, and especially when described in Donald Knuth's The Art of Computer Programming.[10]

The National Archives and Records Administration (NARA) maintains the current rule set for the official implementation of Soundex used by the U.S. Government.[1] These encoding rules are available from NARA, upon request, in the form of General Information Leaflet 55, "Using the Census Soundex".

American Soundex[edit]

The Soundex code for a name consists of a letter followed by three numerical digits: the letter is the first letter of the name, and the digits encode the remaining consonants. Consonants at a similar place of articulation share the same digit so, for example, the labial consonants B, F, P, and V are each encoded as the number 1.

The correct value can be found as follows:

  1. Retain the first letter of the name and drop all other occurrences of a, e, i, o, u, y, h, w.
  2. Replace consonants with digits as follows (after the first letter):
    • b, f, p, v → 1
    • c, g, j, k, q, s, x, z → 2
    • d, t → 3
    • l → 4
    • m, n → 5
    • r → 6
  3. If two or more letters with the same number are adjacent in the original name (before step 1), only retain the first letter; also two letters with the same number separated by 'h' or 'w' are coded as a single number, whereas such letters separated by a vowel are coded twice. This rule also applies to the first letter.
  4. If you have too few letters in your word that you can't assign three numbers, append with zeros until there are three numbers. If you have more than 3 letters, just retain the first 3 numbers.

Using this algorithm, both "Robert" and "Rupert" return the same string "R163" while "Rubin" yields "R150". "Ashcraft" and "Ashcroft" both yield "A261" and not "A226" (the chars 's' and 'c' in the name would receive a single number of 2 and not 22 since an 'h' lies in between them). "Tymczak" yields "T522" not "T520" (the chars 'z' and 'k' in the name are coded as 2 twice since a vowel lies in between them). "Pfister" yields "P236" not "P123" (the first two letters have the same number and are coded once as 'P').


A similar algorithm called "Reverse Soundex" prefixes the last letter of the name instead of the first.

The NYSIIS algorithm was introduced by the New York State Identification and Intelligence System in 1970 as an improvement to the Soundex algorithm. NYSIIS handles some multi-character n-grams and maintains relative vowel positioning, whereas Soundex does not.

Daitch–Mokotoff Soundex (D–M Soundex) was developed in 1985 by genealogist Gary Mokotoff and later improved by genealogist Randy Daitch because of problems they encountered while trying to apply the Russell Soundex to Jews with Germanic or Slavic surnames (such as Moskowitz vs. Moskovitz or Levine vs. Lewin). D–M Soundex is sometimes referred to as "Jewish Soundex" or "Eastern European Soundex",[11] although the authors discourage the use of these nicknames. The D–M Soundex algorithm can return as many as 32 individual phonetic encodings for a single name. Results of D-M Soundex are returned in an all-numeric format between 100000 and 999999. This algorithm is much more complex than Russell Soundex.

As a response to deficiencies in the Soundex algorithm, Lawrence Philips developed the Metaphone algorithm in 1990 for the same purpose. Philips developed an improvement to Metaphone in 2000, which he called Double Metaphone. Double Metaphone includes a much larger encoding rule set than its predecessor, handles a subset of non-Latin characters, and returns a primary and a secondary encoding to account for different pronunciations of a single word in English. Philips created Metaphone 3 as a further revision in 2009 to provide a professional version that provides a much higher percentage of correct encodings for English words, non-English words familiar to Americans, and first and last names found in the United States. It also provides settings that allow more exact consonant and internal vowel matching to allow the programmer to focus the precision of matches more closely.

See also[edit]


  1. ^ a b "The Soundex Indexing System". National Archives and Records Administration. 2007-05-30. Retrieved 2010-12-24. 
  2. ^ "PostgreSQL: Documentation: 9.1: fuzzystrmatch". postgresql.com. Retrieved 2012-11-03. 
  3. ^ "MySQL :: MySQL 5.5 Reference Manual :: 12.5 String Functions - SOUNDEX". dev.mysql.com. 
  4. ^ "SOUNDEX (Transact-SQL)". msdn.microsoft.com. Retrieved 2012-11-03. 
  5. ^ "Soundex". docs.oracle.com. Retrieved 2012-11-03. 
  6. ^ "Phonetic Matching: A Better Soundex". Retrieved 2012-11-03. 
  7. ^ Odell, Margaret King (1956). "The profit in records management". Systems (New York) 20: 20. 
  8. ^ US patent 1261167, R. C. Russell, "(untitled)", issued 1918-04-02  (Archived)
  9. ^ US patent 1435663, R. C. Russell, "(untitled)", issued 1922-11-14  (Archived)
  10. ^ Knuth, Donald E. (1973). The Art of Computer Programming: Volume 3, Sorting and Searching. Addison-Wesley. pp. 391–92. ISBN 978-0-201-03803-3. OCLC 39472999. 
  11. ^ Mokotoff, Gary (2007-09-08). "Soundexing and Genealogy". Retrieved 2008-01-27. 

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Soundex — Please support Wikipedia.
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213 news items

Database Journal
Mon, 09 Mar 2015 00:09:41 -0700

Soundex is a phonetic algorithm for indexing names by sound, as pronounced in English. SOUNDEX codes from different strings can be compared to see how similar the strings sound when spoken. The first character of the code is the first character of the ...

TWCN Tech News (blog)

TWCN Tech News (blog)
Thu, 12 Nov 2015 15:15:00 -0800

Some of the powerful features of RootsMagic Essentials include merge techniques, soundex calculators and potential problems lists. It is highly compatible and allows you to import your family tree details directly from various popular genealogy sites.
Wed, 21 Sep 2005 17:00:00 -0700

Albert Einstein wrote “Make everything as simple as possible, but not simpler.” This principle holds true for most solutions that any programmer, business analyst, or executive will ever implement. What happens, however, when the bridge between ...

The Stack

The Stack
Mon, 21 Sep 2015 06:07:30 -0700

Apparently it is not common OS source code that leads to the suggestion but is more likely to be the implementation of pattern matching under the Soundex and Metaphone phonetic comparison algorithms, as used across spell-checking APIs, including ...

cleveland.com (blog)

cleveland.com (blog)
Thu, 23 Apr 2015 09:38:44 -0700

The nun connected Mulgrew to the International Soundex Reunion Registry, which connected her to her lost daughter. "I have a very fully realized relationship with my daughter and have for the last 18 years," Mulgrew said. "She'll be 38 on the 3rd of May.".


Fri, 24 Apr 2015 10:21:00 -0700

Google says it's working to improve its spam-detection systems in its Google Maps platform after yet another prank allowed a user to upload an inappropriate image to Google Maps. This most recent image, which showed the Google Android mascot urinating ...


Mon, 16 Nov 2015 00:59:37 -0800

Zunächst einmal ist eine Phonetik wie Soundex, Metaphone oder Kölner Phonetik nichts weiter als ein spezieller Zugriffsschlüssel, der seinerseits exakt abgefragt wird. Also eigentlich keine Unschärfe, sondern nur ein alternativer Zugriffscode ...


Fri, 13 Nov 2015 14:30:20 -0800

بعض من ميزات قوية من RootsMagic أساسيات تشمل تقنيات والآلات الحاسبة SOUNDEX وقوائم المشاكل المحتملة دمج. وهو متوافق للغاية ويسمح لك لاستيراد الخاص بك تفاصيل شجرة العائلة مباشرة من مختلف المواقع الأنساب الشعبية. وهو برنامج الأنساب الحرة المرتبطة ...

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