The result is that most reading systems with built-in synthetic speech capabilities will do a decent job with the most common words in any language, but can trip over themselves when trying to pronounce complex compound words, technical terms, proper names, abbreviations, numbers, and the like. Heteronyms—words that are spelled the same way but have different pronunciations and meanings—also offer a challenge, as you can’t always be sure which pronunciation will come out. The word bass in English, for example, is pronounced one way to indicate a fish (bass) and another to indicate an instrument (base).

When you add up the various problem areas, it’s not a surprise why there’s a high frequency of errors. These failings are especially problematic in educational, science, medical, legal, tax, and similar technical publishing fields, as you might expect, as the proper pronunciation of terms is critical to comprehension and being able to communicate with peers.

The ability to correctly voice individual words is a huge benefit to all readers, in other words, which is why you should care about the synthetic rendering quality of your ebooks, as I said I’d get back to. Even if all your readers aren’t going to read your whole book via synthetic speech, everyone comes across words they aren’t sure how to pronounce, weird-looking character names, etc. In the print world, they’d just have to guess at the pronunciation and live with the nuisance of wondering for the rest of the book whether they have the it right in their head or not (barring the rare pronunciation guide in the back, of course).

The embedded dictionaries and pronunciations that reading systems offer are a step up from print, but typically are of little-to-no help in many of these cases, since specialized terms and names don’t appear in general dictionaries. Enhancing your ebooks even just to cover the most complicated names and terms goes a long way to making the entire experience better for all. Enhanced synthetic speech capabilities are a great value-add to set you apart from the crowd, especially if you’re targeting broad audience groups.

Synthetic speech can also reduce the cost to produce audio-enhanced ebooks. Human narration is costly, as I mentioned at the outset, and typically only practical for novels, general non-fiction, and the like. But even in those kinds of books, are you going to have a person narrate the bibliographies and indexes and other complex structures in the back matter, or would it make more sense to leave them to the reader’s device to voice? Having the pronunciation of words consistent across the human-machine divide takes on a little more importance in this light, unless you want to irk your readers with rotten sounding back matter (or worse, omitted material).