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Adding or Improving a Language

Most of the work doesn't need any programming knowledge. Just an understanding of the language, an awareness of its features, patience and attention to detail. Wikipedia is a good source of basic phonetic information, e.g. http://en.wikipedia.org/wiki/Vowel.

In many cases it should be fairly easy to add a rough implementation of a new language, hopefully enough to be intelligible. After that it's a gradual process of improvement.

Language Code

The language is identified using the BCP 47 language tag. When this is not enough to identify an accent, the bcp47-data accents file describes the private use tags used by eSpeak NG. For example:

  • en -- English
  • en-GB-scotland -- English with a Scottish accent
  • en-GB-x-rp -- English with a Received Pronunciation accent
  • es-419 -- Spanish with a Latin American accent
  • fr-CA -- French with a Canadian accent

Language Files

The following files are needed for your language.

  • espeak-data/voices/fr. The voice file. This gives the language name and may set some options.
  • phsource/ph_french. The phoneme definition file. This contains phoneme definitions for the vowels and consonants which the language uses. Usually it will contain mostly vowels. Most consonants will be inherited from the common phoneme definitions in the master phoneme file, phsource/phonemes. The master phoneme file needs to be edited to call your new ph_french file.
  • dictsource/fr_rules. This contains the spelling-to-phoneme translation rules.
  • dictsource/fr_list. This contains pronunciations for numbers, letter and symbol names, and words with exceptional pronunciations. It also gives attributes such as "unstressed" and "pause" to some common words.

The fr_rules and fr_list files are compiled to produce the file espeak-data/fr_dict, which eSpeak uses when it is speaking.

Voice File

Each language needs a voice file in espeak-data/voices or espeak-data/voices/test. The filename of the default voice for a language should be the same as the language code (eg. "fr" for French).

Details of the contents of voice files are given in Voices.

The simplest voice file would contain just 2 lines to give the language name and language code, eg:

name french
language fr

This language code specifies which phoneme table and dictionary to use (i.e. phonemetable fr and espeak-data/fr_dict) to be used. If needed, these can be overridden by phonemes and dictionary attributes in the voice file. For example you may want to start the implementation of a new language by using the phoneme table of an existing language.

Phoneme Definition File

You must first decide on the set of phonemes (vowel and consonant sounds) for the language. These should be defined in a phoneme definition file ph_xxxx, where ph_xxxx is the name of your language. A reference to this file is then included at the end of the master phoneme file, phsource/phonemes, e.g.:

phonemetable fr base
include ph_french

This example defines a phoneme table fr which inherits the contents of phoneme table base. Its contents are found in the file ph_french.

The base phoneme table contains definitions of a basic set of consonants, and also some "control" phonemes such as stress marks and pauses. These are defined in phsource/phonemes. The phoneme table for a language will inherit these, or alternatively it may inherit the phoneme table of another language which in turn inherits the base phoneme table.

The phonemes file for the language defines those additional phonemes which are not inherited (generally the vowels and diphthongs, plus any additional consonants that are needed), or phonemes whose definitions differ from the inherited version (eg. the redefinition of a consonant).

Details of phonemes files are given in Phoneme Tables.

To build the phoneme files, run:

espeak-ng --compile-phonemes

or:

make phsource/phonemes.stamp

For many languages, the consonant phonemes which are already available in eSpeak, together with the available vowel files which can be used to define vowel phonemes, will be sufficient. At least for an initial implementation.

Dictionary Files

Once the language's phonemes have been defined, then pronunciation dictionary data can be produced in order to translate the language's source text into phonemes. This consists of two source files: fr_rules (the spelling to phoneme rules) and fr_list (an exceptions list, and attributes of certain words). The corresponding compiled data file is espeak-data/fr_dict which is produced from the fr_rules and fr_list sources by the command:

espeak-ng --compile=fr

or by:

make fr

Details of the contents of the dictionary files are given in Dictionary.

The fr_list file contains:

  • Pronunciations which exceptions to the rules in fr_rules, (e.g. foreign names).
  • Pronunciation of letter names, symbol names, and punctuation names.
  • Pronunciation of numbers.
  • Attributes for words. For example, common function words which should not be stressed, or conjunctions which should be preceded by a pause.

Program Code

The behaviour of the eSpeak program is controlled by various options such as:

  • Default rules for which syllable of a word has the main stress.
  • Relative lengths and amplitude of vowels in stressed and unstressed syllables.
  • Which intonation tunes to use.
  • Rules for speaking numbers.

The function SetTranslator() at the start of the source code file tr_languages.c recognizes the language code and sets the appropriate options. For a new language, you would add its language code and the required options in SetTranslator(). However, this may not be necessary during testing because most of the options can also be set in the voice file in espeak-data/voices (see Voice Files).

Compiling Rules File for Debugging

When espeak-ng is invoked with -X parameter, it shows more detailed trace of chosen language rules for pronunciation. This trace can show line numbers also, if language is compiled with --compile-debug option.

To do this, go to espeak-ng project root folder, then:

cd dictsource
../src/espeak-ng --compile-debug=en

When invoked in following way:

espeak-ng -ven -X "Test."

It will show:

Translate 'test'
  1  5965:  t [t]

  1  2104:  e [E]

  1  5725:  s [s]

  1  5965:  t [t]

 t'Est

Improving a Language

Listen carefully to the eSpeak voice. Try to identify what sounds wrong and what needs to be improved.

  • Make the spelling-to-phoneme translation rules more accurate, including the position of stressed syllables within words. Some languages are easier than others. I expect most are easier than English.

  • Improve the sounds of the phonemes. It may be that a phoneme should sound different depending on adjacent sounds, or whether it's at the start or the end of a word, between vowels, in a stressed or unstressed syllable, etc. This may consist of making small adjustments to vowel and diphthong quality or length, or adjusting the strength of consonants. Phoneme definitions can include conditional statements which can be used to change the sound of a phoneme depending on its environment. Bigger changes may be recording new or replacement consonant sounds, or may even need program code to implement new types of sounds.

  • Some common words should be added to the dictionary (the fr_list file for the language) with an "unstressed" attribute $u or $u+ (e.g. in English, words such as "the", "is", "had", "my", "she", "of", "in", "some"), or should be preceded by a short pause (such as "and", "but", "which"), or have other attributes, in order to make the speech flow better.

  • Improve the rhythm of the speech by adjusting the relative lengths of vowels in different contexts, e.g. stressed/unstressed syllable, or depending on the following phonemes. This is important for making the speech sound good for the language.

  • Make new intonation "tunes" for statements or questions (see Intonation).

For most of the eSpeak voices, I do not speak or understand the language, and I do not know how it should sound. I can only make improvements as a result of feedback from speakers of that language. If you want to help to improve a language, listen carefully and try to identify individual errors, either in the spelling-to-phoneme translation, the position of stressed syllables within words, or the sound of phonemes, or problems with rhythm and vowel lengths.