encoding phonetic tone letters

From: peter_constable@sil.org
Date: Fri Sep 10 1999 - 15:35:32 EDT

       Since we're on the topic of phonetic symbols, I've got an idea
       to throw out for feedback. IPA provides for indicating tones
       using tone letters, but only five are defined in Unicode U+02E5
       - 02E9, which represent five levels. A lot more is needed for
       representing tones, however: if you look at the chart of IPA
       symbols at http://www.arts.gla.ac.uk/IPA/fullchart.html you'll
       see five contour letters followed by "etc.". I.e. these are
       only a pattern.

       In practice, 5 tone levels cover most situations, but I've
       heard of 7 being needed in some situations. I have also
       encountered contours that are sequences of up to 3 tones long.
       Supposing up to 7 levels and sequences of 1 - 3 in length, the
       possible combinations come to something like 400 in all. Now, I
       don't think any of us are enamoured with the thought of adding
       400 tone letters to the standard. In place of that, though, 8
       characters for tone letters could be sufficient: 7 to indicate
       tone levels, and 1 to demarcate the begnnings of sequences.
       (Where contours are not involved, the delimiter isn't needed.)
       Given that there are 5 characters already, we'd only be looking
       at 3 more (assuming 7 is really what's needed to cover all
       situations). It would be up to some smart font technology, such
       as AAT or OpenType, to substitute actual contour glyphs for the
       sequences; in the absence of smart fonts, a sequence of level
       tone letters are shown, and the delimiter either appears as a
       small visual delimiter or is zero-width.

       Is this an idea worth considering?


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