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Text to Phoneme Translation

Translation Files

There is a separate set of pronunciation files for each language, their names starting with the language name.

There are two separate methods for translating words into phonemes:

  • Pronunciation Rules. These are an attempt to define the pronunciation rules for the language. The source file is: <language>_rules (e.g. en_rules).

  • Lookup Dictionary. A list of individual words and their pronunciations and/or various other properties. The source files are: <language>_list (e.g. en_list) and optionally <language>_extra (e.g. en_extra).

These files are compiled into the file <language>_dict  in the espeak-ng-data directory (e.g. espeak-ng-data/en_dict).

Phoneme names

Each of the language's phonemes is represented by a mnemonic of 1, 2, 3, or 4 characters. Together with a number of utility codes (eg. stress marks and pauses), these are defined in the phoneme data file.

The utility 'phonemes' are:

Symbol Description
' primary stress
, secondary stress
% unstressed syllable
= put the primary stress on the preceding syllable
_: short pause
_ a shorter pause
| use to separate two adjacent characters, to prevent them from being considered as a single multi-character phoneme
|| indicates a word boundary within a phonetic string

It is not necessary to specify the stress of every syllable. Stress markers are only needed in order to change the effect of the language's default stress rule.

The phonemes which are used to represent a language's sounds are based loosely on the Kirshenbaum (ASCII-IPA) representation of the International Phonetic Alphabet.

Full list of commonly used phonemes can be found in the phsource/phonemes file.

Pronunciation Rules

The rules in the <language>_rules file specify the phonemes which are used to pronounce each letter, or sequence of letters. Some rules only apply when the letter or letters are preceded by, or followed by, other specified letters.

To find the pronunciation of a word, the rules are searched and any which match the letters at the in the word are given a score depending on how many letters are matched. The pronunciation from the best matching rule is chosen. The pointer into the source word is then advanced past those letters which have been matched and the process is repeated until all the letters of the word have been processed.

Rule Groups

The rules are organized in groups, each starting with a .group line:

  • .group <character> A group for each letter or character.

  • .group <2 characters> Optional groups for some common 2 letter combinations. This is only needed, for efficiency, in cases where there are many rules for a particular letter. They would not be needed for a language which has regular spelling rules. The first character can only be an ascii character (less than 0x80).

notes about rule groups

When matching a word, firstly the 2-letter group for the two letters at the current position in the word (if such a group exists) is searched, and then the single-letter group. The highest scoring rule in either of those two groups is used.

  • .group A group for other characters which don't have their own group.

  • .replace See section Character Substitution.

Letter groups

Specific group of rules is declaration of letter sequences with some common feature of letters for particular language. It may be used as a placeholder of prefixes/infixes of words (in prerules) or infixed/postfixes in (postrules).

  • .L<nn> Defines a group of letter sequences, any of which can match with Lnn in a pre or post rule (see below). nn is a 2 digit decimal number in the range 01 to 94. e.g.: .L01 b bl br pl pr

notes about letter groups

There can be up to 200 items in one letter group.

When matching a word, firstly the group containing most letters is checked at the current position in the word (if such a group exists), then shorter ones till to the single-letter groups. The highest scoring rule of matching group is used.

~ Letter in letter group means, that there can be no letter in this group in the pre- or post- rule.

Example with prerule group:

.L01 ~ b c
.group a
  L01) a      i  // A

following rules will match for words:

Word Phonetic spelling
base bice
case cice
ace ice

Example with postrule group:

.L01 ~ b c
.group a
       a (L01 u
Word Phonetic spelling
tab tub
mac muc
tea teu

Rules

Each rule is on separate line, and has the syntax:

[<pre>)] <match> [(<post>] <phoneme string>
  • characters in <pre>) group are already spelled and "consumed"
  • characters in <match> group are ones which will be spelled and "consumed" by best matching rule
  • characters in (<post> group will not be spelled and produced, but can be used as reference to choose matching rule

Note that <match> group can be longer than name of character group, but cannot be shorter.

Example:

.group o
       o      0   // "o" is pronounced as [0], one letter consumed
       oo     u:  // but "oo" is pronounced as [u:], two letters consumed
    b) oo (k  U   // pronounced as [U], two letters consumed

oo is pronounced as [u:], but when also preceded by b and followed by k, it is pronounced [U]. If

In the case of a single-letter group, the first character of <match> much be the group letter. In the case of a 2-letter group, the first two characters of <match> must be the group letters. The second and third rules above may be in either .group o or .group oo

Alphabetic characters in the <pre>, <match>, and <post> parts must be lower case, and matching is case-insensitive. Some upper case letters are used in <pre> and <post> with special meanings.

Special characters in <phoneme string>:

  • _^_<language code> Translate using a different language.

If this rule is selected when translating a word, then the translation is aborted and the word is re-translated using the specified different language. <language code> may be upper or lower case. This can be used to recognise certain letter combinations as being foreign words and to use the foreign pronunciation for them. e.g.:

th (_    _^_EN

indicates that a word which ends in th is translated using the English translation rules and spoken with English phonemes.

Special Characters in both <pre> and <post>

Symbol Description
_ Beginning or end of a word (or a hyphen).
- Hyphen.
A Any vowel1.
C Any consonant 1.
B H F G Y These may indicate other sets of characters1.
L<nn> Any of the sequence of characters defined as a letter grup.
D Any digit.
K Not a vowel (i.e. a consonant or word boundary or non-alphabetic character).
X There is no vowel until the word boundary.
Z A non-alphabetic character.
% Doubled (placed before a character in <pre> and after it in <post>.
/ The following character is treated literally.
\xxx Character is written as by 3 digit octal value of xxx
@ One syllable (i.e. at least one vowel or diphthong)

Examples of rules:

        _)  a        A       // "a" at the start of a word
            a (CC    A       // "a" followed by two consonants
            a (C%    A       // "a" followed by a double consonant (the same letter twice)
            a (/%    A       // "a" followed by a percent sign
        %C) a        A       // "a" preceded by a double consonants
        @@) bi       bI      // "bi" preceded by at least two syllables
       @@a) bi       bI      // "bi" preceded by at least 2 syllables and following 'a'

         @) ly (_S2  lI       // "ly", at end of a word with at least one other
                              // syllable, is a suffix pronounced [lI].  Remove
                              // it and retranslate the word.
        
         _) un (@P2  %Vn      // "un" at the start of a word is an unstressed
                              // prefix pronounced [Vn]

Note, that:

  1. Matching characters in the <pre> part do not affect the syllable counting.
  2. Word end mark can't be used with syllable mark. E.g. _@) or @_ will not work, but you can use @) ... (+ or ... (@+ to make rule with only one syllable prevail rule with more syllables.

Special characters only in <pre>:

Symbol Description
& A syllable which may be stressed (i.e. is not defined as unstressed).
V Matches only if a previous word has indicated that a verb form is expected.
xxJ Skip letters until xx. Simple xx means start of current word. xx_yy means xx as end of previous and yy as start of current word. If necessary, more than one J can be used, and Lxx group as letter mark.

e.g.

      get_J)  a   i      // for `get ada` will say `get adi`
       setJ)  a   o      // for `set ada` will say `set oda`
      ge_tJ)  a   i:     // for `ge tada` will say `get adi:`

Special characters only in <post>:

Symbol Description
+ Force an increase in the score in this rule by 20 points (may be repeated for more effect).
< Force a decrease in the score in this rule by 20 points (may be repeated for more effect).
Jxx Skip letters until xx. Simple xx means end of current word. xx_yy means xx as end of current and yy as start of next word. If necessary, more than one J can be used, and Lxx group as letter mark.
S<number> This number of matching characters are a standard suffix, remove them and retranslate the word.
P<number> This number of matching characters are a standard prefix, remove them and retranslate the word.
Lnn nn is a 2-digit decimal number in the range 01 to 20 Matches with any of the letter sequences which have been defined for letter group nn
N Only use this rule if the word is not a retranslation after removing a suffix.
# (English specific) change the next "e" into a special character "E"
$noprefix Only use this rule if the word is not a retranslation after removing a prefix.
$w_alt Only use this rule if the word is $w_alt2 found in the *_list file with the $w_alt3, $alt, $alt2 or $alt3 attribute respectively.
$p_alt Only use this rule if the part-word, $p_alt2 up to and including the pre and $p_alt3 match parts of this rule, is found in the *_list file with the $alt, $alt2 or $alt3 attribute respectively.

e.g.

_) un (i      ju:    // ... except in words starting "uni"
_) un (inP2   ,Vn    // ... but it is for words starting "unin"
        a (J_get  u      // for `ada get` will say `uda get`
        a (Jset   e      // for `ada set` will say `ade set`
        a (Jg_et  u:     // for `adag et` will say `u:dag et`

S and P must be at the end of the <post> string.

S<number> may be followed by additional letters (e.g. S2ei). Some of these are probably specific to English, but similar functions could be made for other languages.

P<number> may be followed by additional letters (e.g. P3v).

Symbol Description
q Query the *_list file to find stress position or other attributes for the stem, but don't re-translate the word with the suffix removed.
t Determine the stress pattern of the word before adding the suffix.
d The previous letter may have been doubled when the suffix was added.
e e may have been removed.
i y may have been changed to i.
v The suffix means the verb form of pronunciation should be used.
f The suffix means the next word is likely to be a verb.
m After this suffix has been removed, additional suffixes may be removed.
t Determine the stress pattern of the word before adding the prefix.

Pronunciation Dictionary List

The <language>_list file contains a list of words whose pronunciations are given explicitly, rather than determined by the Pronunciation Rules. The <language>_extra file, if present, is also used and it's contents are taken as coming after those in <language>_list.

Also the list can be used to specify the stress pattern, or other properties, of a word.

If the Pronunciation rules are applied to a word and indicate a standard prefix or suffix, then the word is again looked up in Pronunciation Dictionary List after the prefix or suffix has been removed.

Lines in the dictionary list have the form:

<word>     [<phoneme string>]     [<flags>]

e.g.

book      bUk

Rather than a full pronunciation, just the stress may be given, to change where it would be otherwise placed by the Pronunciation Rules:

berlin       $2      // stress on second syllable
absolutely   $3      // stress on third syllable
for          $u      // an unstressed word

Multiple Words

A pronunciation may also be specified for a group of words, when these appear together. Up to four words may be given, enclosed in brackets. This may be used for change the pronunciation or stress pattern when these words occur together,

(de jure)    deI||dZ'U@rI2   // note || used as a word break in the phoneme string

or to run them together, pronounced as a single word

(of a)       @v@

or to give them a flag when they occur together

(such as)    sVtS||a2z   $pause        // precede with a pause

Hyphenated words in the <language>_list file must also be enclosed within brackets, because the two parts are considered as separate words.

Special characters in <phoneme string>:

Symbol Description
_^_<language code> Translate using a different language. See explanation above.

Flags

A word (or group of words) may be given one or more flags, either instead of, or as well as, the phonetic translation.

Symbol Description
$1 Primary stress on the 1st syllable.
$2 Primary stress on the 2nd syllable.
$3 Primary stress on the 3rd syllable.
$4 Primary stress on the 4th syllable.
$5 Primary stress on the 5th syllable.
$6 Primary stress on the 6th syllable.
$7 Primary stress on the 7th syllable.
$u The word is unstressed. In the case of a multi-syllable word, a slight stress is applied according to the default stress rules.
$u1 The word is unstressed, with a slight stress on its 1st syllable.
$u2 The word is unstressed, with a slight stress on its 2nd syllable.
$u3 The word is unstressed, with a slight stress on its 3rd syllable.
$u+ $u1+ $u2+ $u3+ As above, but the word has full stress if it's at the end of a clause.
$pause Ensure a short pause before this word (eg. for conjunctions such as "and", some prepositions, etc). Does not apply for 1st, 2nd or last word of a sentence.
$brk Ensure a very short pause before this word, shorter than $pause (eg. for some prepositions, etc). Does not apply for the last word of a sentence.
$only The rule does not apply if a prefix or suffix has already been removed.
$onlys As $only, except that a standard plural ending is allowed.
$stem The rule only applies if a suffix has already been removed (i.e. word had to have suffix before).
$strend Word is fully stressed if it's at the end of a clause.
$strend2 As $strend, but the word is also stressed if followed only by unstressed word(s).
$unstressend Word is unstressed if it's at the end of a clause.
$abbrev This has two meanings. If there is no phoneme string: Speak the word as individual letters, even if it contains a vowel (eg. "abc" should be spoken as "a" "b" "c"). If there is a phoneme string: This word is capitalized because it is an abbreviation and capitalization does not indicate emphasis (if the "emphasize all-caps" is on).
$double Cause a doubling of the initial consonant of the following word (used e.g. for Italian and Finnish).
$alt $alt2 .. $alt7 These 7 groups are language specific. Their use should be described in the language's *_list file. $alt and $alt1 are synonyms.
$combine This word is treated as though it is combined with the following word with a hyphen. This may be subject to further conditions for certain languages.
$dot Ignore a . after this word even when followed by a capital letter (e.g. Mr. and Dr.).
$hasdot Use this pronunciation if the word is followed by a dot. (This attribute also implies $dot).
$max3 Limit to 3 repetitions in pronunciation.
$text Word translates to replacement text, not phonemes.
$verbf The following word is probably a verb.
$verbsf The following word is probably a verb if it has an "s" suffix.
$nounf The following word is probably a noun.
$pastf The following word is probably past tense.
$verb Use this pronunciation if it's a verb, i.e. previously processed word had $verbf or $verbsf set.
$noun Use this pronunciation if it's a noun, i.e. previously processed word had $nounf set.
$past Use this pronunciation if it's past tense, i.e. previously processed word had $pastf set.
$verbextend Extend the influence of $verbf and $verbsf until a word with $verb or $nounf is encountered.
$capital Use this pronunciation if the word has initial capital letter (eg. polish v Polish).
$allcaps Use this pronunciation if the word is all capitals.
$accent Used for the pronunciation of a single alphabetic character. The character name is spoken as the base-letter name plus the accent (diacritic) name. e.g. It can be used to specify that "â" is spoken as "a" "circumflex".
$accent_before used with accent names, say this accent name before the letter name.
$atstart Use this pronunciation if it's at the start of a clause.
$atend Use this pronunciation if it's at the end of a clause.
$sentence The rule only applies if the clause includes end-of-sentence (i.e. terminator is {. ? !} not {, ; :}). For example, $atend $sentence means that the rule only applies at the end of a sentence.
$native Not used, if switched to other translation.

The last group are probably English specific, but something similar may be useful in other languages. They are a crude attempt to improve the accuracy of pairs like ob'ject (verb) v 'object (noun) and read (present) v read (past).

The dictionary list is searched from bottom to top. The first match that satisfies any conditions is used (i.e. the one lowest down the list). So if we have:

to    t@               // unstressed version
to    tu:   $atend     // stressed version

then if to is at the end of the clause, we get [tu:], if not then we get [t@].

Translating a Word to Another Word

Rather than specifying the pronunciation of a word by a phoneme string, you can specify another "sounds like" word.

Use the attribute $text e.g.

cough    coff   $text

Alternatively, use the command $textmode on a line by itself to turn this on for all subsequent entries in the file, until it's turned off by $phonememode. e.g.

$textmode
cough     coff
through   threw
$phonememode

This feature cannot be used for the special entries in the *_list files which start with an underscore, such as numbers.

Currently textmode entries are only recognized for complete words, and not for stems from which a prefix or suffix has been removed (e.g. the word "coughs" would not match the example above).

Conditional Rules

Rules in a *_rules file and entries in a *_list file can be made conditional. They apply only to some voices. This can be useful to specify different pronunciations for different variants of a language (dialects or accents).

Conditional rules have ? and a condition number at the start if the line in the *_rules or *_list file. This means that the rule only applies of that condition number is specified in a dictrules line in the voice file.

If the rule starts with ?! then the rule only applies if the condition number is not specified in the voice file. e.g.

?3     can't     kant    // only use this if the voice has:  dictrules 3
?!3    rather    rA:D3   // only use if the voice doesn't have:  dictrules 3

Numbers and Character Names

Letter names

The names of individual letters can be given either in the *_rules or *_list file. Sometimes an individual letter is also used as a word in the language and its pronunciation as a word differs from its letter name. If so, it should be listed in the *_list file, preceded by an underscore, to give the letter name (as distinct from its pronunciation as a word). e.g. in English:

_a   eI

Numbers

The operation the TranslateNumber() function is controlled by the language's langopts.numbers option. This constructs spoken numbers from fragments according to various options which can be set for each language. The number fragments are given in the *_list file.

Symbol Description
_0 to _9 The numbers 0 to 9.
_13 etc. Any pronunciations which are needed for specific numbers in the range _10 to _99.
_2X _3X Twenty, thirty, etc., used to make numbers 10 to 99.
_0C The word for hundred.
_1C _2C Special pronunciation for one hundred, two hundred, etc., if needed.
_1C0 Special pronunciation (if needed) for 100 exactly.
_0M1 The word for thousand.
_1M1 _2M1 Special pronunciation for 1 thousand, 2 thousand, etc, if needed.
_0M2 The word for million.
_0M3 The word for 1,000,000,000.
_0MX The word for 10^3X of number1.
_0and Word for and when speaking numbers (e.g. two hundred and twenty).
_dpt Word spoken for the decimal point/comma.
_dpt2 Word spoken (if any) at the end of all the digits after a decimal point.

notes about ordinal numbers To enable ordinal numbers:

  1. set langopts.numbers | NUM_ORDINAL_DOT in tr_languages.c
  2. for each number symbol explained above, add a line with suffix o. For example: _1o for first, _51o for fifty first and so on.

Character Substitution

Character substitutions can be specified by using a .replace section at the start of the *_rules file. In each line multiple source characters can be replaced by one or two characters. This substitution is done to a word before word is searched in *_list or *_listx file and translated using the spelling-to-phoneme rules. Only the lower-case version of the characters needs to be specified. e.g.:

.replace
   ô   ő   // (Hungarian) allow the use of o-circumflex instead of o-double-accute
   û   ű
   cx  ĉ   // (Esperanto) allow "cx" as an alternative to c-circumflex
   fi   fi  // replace a single character ligature by two characters

(Re)definition of character groups

The set of these vowel characters in A group and consonants in C group may be redefined for a particular language. Other sets of letters indicated by B, E, F and G usually have specific meaning for each particular language.

(Re)definition of letter groups is done in tr_languages.c file by calling SetLetterBits() function from (usually) NewTranslator() function. Note, that letters should be stored as array of chars, thus multibyte unicode letters should be transposed using transpose_min and transpose_max parameters of particular Translator structure, or using SetLetterBitsUTF8() function.

1. Default length, to switch between named orders and just spelled digits in number, is 14 digits and is set in tr->langopts.max_digits field of NewTranslator function of tr_languages.c file. To change it, update SelectTranslator function for particular language.