Strings and Names

Many HTK definition files include names of various types of objects: for example labels, model names, words, etc. In order to achieve some uniformity, HTK applies standard rules for reading strings which are names. These rules are not, however, necessary when using the language modelling tools - see below.

A name string consists of a single white space delimited word or a quoted string. Either the single quote ' or the double quote " can be used to quote strings but the start and end quotes must be matched. The backslash \ character can also be used to introduce otherwise reserved characters. The character following a backslash is inserted into the string without special processing unless that character is a digit in the range 0 to 7. In that case, the three characters following the backslash are read and interpreted as an octal character code. When the three characters are not octal digits the result is not well defined.

In summary the special processing is

Notation	Meaning
\\	\
\_	represents a space that will not terminate a string
\'	' (and will not end a quoted string)
\"	" (and will not end a quoted string)
\nnn	the character with octal code \nnn

Note that the above allows the same effect to be achieved in a number of different ways. For example,

    "\"QUOTE" 
    \"QUOTE 
    '"QUOTE' 
    \042QUOTE

all produce the string "QUOTE.

The only exceptions to the above general rules are:

• Where models are specified in HHED scripts, commas (,), dots (.), and closing brackets ()) are all used as extra delimiters to allow HHED scripts created for earlier versions of HTK to be used unchanged. Hence for example, (a,b,c,d) would be split into 4 distinct name strings a, b, c and d.

• When the configuration variable RAWMITFORMAT is set true, each word in a language model definition file consists of a white space delimited string with no special processing being performed.

• Source dictionaries read by HDMAN are read using the standard HTK string conventions, however, the command IR can be used in a HDMAN source edit script to switch to using this raw format.

• To ensure that the general definition of a name string works properly in HTK master label files, all MLFs must have the reserved . and /// terminators alone on a line with no surrounding white space. If this causes problems reading old MLF files, the configuration variable V1COMPAT should be set true in the module HLABEL. In this case, HTK will attempt to simulate the behaviour of the older version 1.5.

• To force numbers to be interpreted as strings rather than times or scores in a label file, they must be quoted. If the configuration variable QUOTECHAR is set to ' or " then output labels will be quoted with the specified quote character. If QUOTECHAR is set to \, then output labels will be escaped. The default is to select the simplest quoting mechanism.

Note that under some versions of Unix HTK can support the 8-bit character sets used for the representation of various orthographies. In such cases the shell environment variable $LANG usually governs which ISO character set is in use.