Festival Speech Synthesis System: - Speech Resource Pages

lexicon by over 90%. The function reduce_lexicon in `festival/lib/lts_build.scm' was used to do
this. A diccussion of using the above technique as a dictionary compression method is discussed in pagel98. A
morphological decomposition algorithm, like that described in black91, may even help more.
The technique described in this section and its relative merits with respect to a number of languages/lexicons and
tasks is dicussed more fully in black98.
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13.6 Lexicon requirements
For English there are a number of assumptions made about the lexicon which are worthy of explicit mention. If you
are basically going to use the existing token rules you should try to include at least the following in any lexicon that
is to work with them.
● The letters of the alphabet, when a token is identified as an acronym it is spelled out. The tokenization
assumes that the individual letters of the alphabet are in the lexicon with their pronunciations. They should be
identified as nouns. (This is to distinguish a as a determiner which can be schwa'd from a as a letter which
cannot.) The part of speech should be nn by default, but the value of the variable token.letter_pos is
used and may be changed if this is not what is required.
● One character symbols such as dollar, at-sign, percent etc. Its difficult to get a complete list and to know what
the pronunciation of some of these are (e.g hash or pound sign). But the letter to sound rules cannot deal with
them so they need to be explicitly listed. See the list in the function mrpa_addend in
`festival/lib/dicts/oald/oaldlex.scm'. This list should also contain the control characters
and eight bit characters.
● The possessive 's should be in your lexicon as schwa and voiced fricative (z). It should be in twice, once as
part speech type pos and once as n (used in plurals of numbers acronyms etc. e.g 1950's). 's is treated as a
word and is separated from the tokens it appears with. The post-lexical rule (the function
postlex_apos_s_check) will delete the schwa and devoice the z in appropriate contexts. Note this postlexical
rule brazenly assumes that the unvoiced fricative in the phoneset is s. If it is not in your phoneset copy
the function (it is in `festival/lib/postlex.scm') and change it for your phoneset and use your
version as a post-lexical rule.
● Numbers as digits (e.g. "1", "2", "34", etc.) should normally not be in the lexicon. The number conversion
routines convert numbers to words (i.e. "one", "two", "thirty four", etc.).
● The word "unknown" or whatever is in the variable token.unknown_word_name. This is used in a few
obscure cases when there just isn't anything that can be said (e.g. single characters which aren't in the lexicon).
Some people have suggested it should be possible to make this a sound rather than a word. I agree, but
Festival doesn't support that yet.
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13.7 Available lexicons
Currently Festival supports a number of different lexicons. They are all defined in the file `lib/lexicons.scm'
each with a number of common extra words added to their addendas. They are
`CUVOALD'
The Computer Users Version of Oxford Advanced Learner's Dictionary is available from the Oxford Text
Archive ftp://ota.ox.ac.uk/pub/ota/public/dicts/710. It contains about 70,000 entries and is a part of the BEEP
lexicon. It is more consistent in its marking of stress though its syllable marking is not what works best for our
synthesis methods. Many syllabic `l''s, `n''s, and `m''s, mess up the syllabification algorithm, making
results sometimes appear over reduced. It is however our current default lexicon. It is also the only lexicon
with part of speech tags that can be distributed (for non-commercial use).
`CMU'
This is automatically constructed from `cmu_dict-0.4' available from many places on the net (see