How to fix poor TTS pronunciation

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Dec 19, 2008
Boston, MA, USA
<img src="/styles/default/custom/flags/us.png" alt="United States" /> United States
TomTom Model(s)
Tomtom GO for Android
After many many hours, I figured out a workaround for the poor TTS on most Tomtom devices.

It impacts all devices that use Loquendo (except maybe the really old GO 910). It does not impact devices that use Vocalizer (ONE-XLS from 2007, ONE 125S, ONE130S, XL325S, XL330S, and iPhone).

To fix TTS, go to your map folder (usually "North America" or "Usa_Canada_and_Mexico") and look for the file cphoneme.dat. Rename this file cphoneme.old.

After that most of your TTS will be fine. If there are any words that are still mispronounced, you can fix them by using notepad to edit the following files:
- \LoquendoTTS\data\roadnrEnglishUS.lex (all models except the GO 720/920)
- \LoquendoTTS\EnglishUs\roadnr.EnglishUs6.8.lex (for the GO 720/920)

Thanks to misterbk, canderson, and malouff for all the additional background research that helped me isolate this fix.

cphoneme.dat is the Teleatlas hint file, that processes localized hints before the Loquendo hint file processes. The problem is that the cphoneme.dat file appears to be using special characters that Loquendo doesn't understand. Many times when words are pulled from cphoneme, the Loquendo error log says it cannot interpret them. Further, when this interpretation error happens, Tomtom stops looking at the roadnrEnglish and EnglishUS.dbl hint files. Loquendo does a great job on its own pronouncing these words without Teleatlas's assistance, as evidenced by the demo at

I hope this helps others, I tested it through a variety of problem roads ("Boston", "San Francisco", etc).
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