Class LetterToSoundImpl

java.lang.Object
com.sun.speech.freetts.lexicon.LetterToSoundImpl
All Implemented Interfaces:
LetterToSound

public class LetterToSoundImpl extends Object implements LetterToSound
Provides the phone list for words using the CMU6 letter-to-sound (LTS) rules, which are based on the Black, Lenzo, and Pagel paper, "Issues in Building General Letter-to-Sound Rules." Proceedings of ECSA Workshop on Speech Synthesis, pages 77-80, Australia, 1998.

The LTS rules are a simple state machine, with one entry point for each letter of the alphabet (lower case letters are always assumed, and the rules keep an array with one entry per letter that point into the state machine).

The state machine consists of a huge array, with most entries containing a decision and the indices of two other entries. The first of these two indices represents where to go if the decision is true, and the second represents where to go if the decision is false. All entries that do not contain a decision are final entries, and these contain a phone.

The decision in this case is a simple character comparison, but it is done in the context of a window around the character in the word. The decision consists of a index into the context window and a character value. If the character in the context window matches the character value, then the decision is true.

The machine traversal for each letter starts at that letter's entry in the state machine and ends only when it reaches a final state. If there is no phone that can be mapped, the phone in the final state is set to 'epsilon.'

The context window for a character is generated in the following way:

  • Pad the original word on either side with '#' and '0' characters the size of the window for the LTS rules (in this case, the window size is 4). The "#" is used to indicate the beginning and end of the word. So, the word "monkey" would turn into "000#monkey#000".
  • For each character in the word, the context window consists of the characters in the padded form the preceed and follow the word. The number of characters on each side is dependent upon the window size. So, for this implementation, the context window for the 'k' in monkey is "#money#0".

Here's how the phone for 'k' in 'monkey' might be determined:

  • Create the context window "#money#0".
  • Start at the state machine entry for 'k' in the state machine.
  • Grab the 'index' from the current state. This represents an index into the context window.
  • Compare the value of the character at the index in the context window to the character from the current state. If there is a match, the next state is the qtrue value. If there isn't a match, the next state is the qfalse state.
  • Keep on working through the machine until you read a final state.
  • When you get to the final state, the phone is the character in that state.

This implementation will either read from a straight ASCII file or a binary file. When reading from an ASCII file, you can specify when the input line is tokenized: load, lookup, or never. If you specify 'load', the entire file will be parsed when it is loaded. If you specify 'lookup', the file will be loaded, but the parsing for each line will be delayed until it is referenced and the parsed form will be saved away. If you specify 'never', the lines will parsed each time they are referenced. The default is 'load'. To specify the load type, set the system property as follows:

   -Dcom.sun.speech.freetts.lexicon.LTSTokenize=load
 

[[[TODO: This implementation uses ASCII 'a'-'z', which is not internationalized.]]]

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected HashMap
    The indexes of the starting points for letters in the state machine.
    protected boolean
    If true, the state string is tokenized when it is first read.
    protected boolean
    If true, the state string is tokenized the first time it is referenced.
  • Constructor Summary

    Constructors
    Constructor
    Description
    LetterToSoundImpl(URL ltsRules, boolean binary)
    Class constructor.
  • Method Summary

    Modifier and Type
    Method
    Description
    boolean
    Compares this LTS to another for debugging purposes.
    void
    Dumps a binary form of the letter to sound rules.
    protected char[]
    Makes a character array that looks like "000#word#000".
    getPhones(String word, String partOfSpeech)
    Calculates the phone list for a given word.
    protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State
    getState(int i)
    Gets the State at the given index.
    protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State
    Gets the State based upon the String.
    protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State
    getState(String type, StringTokenizer tokenizer)
    Gets the State based upon the type and tokenizer.
    static void
    main(String[] args)
    Translates between text and binary forms of the CMU6 LTS rules.
    protected void
    Creates a word from the given input line and add it to the state machine.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • tokenizeOnLoad

      protected boolean tokenizeOnLoad
      If true, the state string is tokenized when it is first read. The side effects of this are quicker lookups, but more memory usage and a longer startup time.
    • tokenizeOnLookup

      protected boolean tokenizeOnLookup
      If true, the state string is tokenized the first time it is referenced. The side effects of this are quicker lookups, but more memory usage.
    • letterIndex

      protected HashMap letterIndex
      The indexes of the starting points for letters in the state machine.
  • Constructor Details

    • LetterToSoundImpl

      public LetterToSoundImpl(URL ltsRules, boolean binary) throws IOException
      Class constructor.
      Parameters:
      ltsRules - a URL pointing to the text containing the letter to sound rules
      binary - if true, the URL is a binary source
      Throws:
      NullPointerException - if the ltsRules are null
      IOException - if errors are encountered while reading the compiled form or the addenda
  • Method Details

    • parseAndAdd

      protected void parseAndAdd(String line)
      Creates a word from the given input line and add it to the state machine. It expects the TOTAL line to come before any of the states.
      Parameters:
      line - the line of text from the input file
    • dumpBinary

      public void dumpBinary(String path) throws IOException
      Dumps a binary form of the letter to sound rules. This method is not thread-safe.

      Binary format is:

         MAGIC
         VERSION
         NUM STATES
         for each state ...
       
      Parameters:
      path - the path to dump the file to
      Throws:
      IOException - if a problem occurs during the dump
    • getState

      protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State getState(int i)
      Gets the State at the given index. This may replace a String at the current spot with an actual State instance.
      Parameters:
      i - the index into the state machine
      Returns:
      the State at the given index.
    • getState

      protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State getState(String s)
      Gets the State based upon the String.
      Parameters:
      s - the string to parse
      Returns:
      the parsed State
    • getState

      protected com.sun.speech.freetts.lexicon.LetterToSoundImpl.State getState(String type, StringTokenizer tokenizer)
      Gets the State based upon the type and tokenizer.
      Parameters:
      type - one of STATE or PHONE
      tokenizer - a StringTokenizer containing the State
      Returns:
      the parsed State
    • getFullBuff

      protected char[] getFullBuff(String word)
      Makes a character array that looks like "000#word#000".
      Parameters:
      word - the original word
      Returns:
      the padded word
    • getPhones

      public String[] getPhones(String word, String partOfSpeech)
      Calculates the phone list for a given word. If a phone list cannot be determined, null is returned. This particular implementation ignores the part of speech.
      Specified by:
      getPhones in interface LetterToSound
      Parameters:
      word - the word to find
      partOfSpeech - the part of speech.
      Returns:
      the list of phones for word or null
    • compare

      public boolean compare(LetterToSoundImpl other)
      Compares this LTS to another for debugging purposes.
      Parameters:
      other - the other LTS to compare to
      Returns:
      true if these are equivalent
    • main

      public static void main(String[] args)
      Translates between text and binary forms of the CMU6 LTS rules.