To demonstrate the trouble with unit-selection voices for language learning, below are some example Chinese mistakes that I found, usually after just a few minutes of experimenting with each voice.
| Synthesizer | Input | Problem |
|---|---|---|
| Google Translate (2011-05, using SVOX Yun which is also used by Android) | 继续学院 | The 学 is only half-pronounced. It seems like they had a recording of a whole 学 but some program played only half of it. You can't really hear the '-ue' of the 'xue'. |
| 糖尿病 | 'n' of 尿 unclear | |
| 深省 | Google correctly says this is "shēn xǐng", but its voice incorrectly says "shēn shěng" (the voice must be using a smaller dictionary than the transcriber) | |
| 绝 | somewhat unclear when spoken in isolation | |
| Beijing Infoquick SinoVoice (2011-05) | 用出来 | The main word 用 could be clearer; at least 来 (and possibly 出) should be neutral tone (轻声) but isn't |
| iFlyTek InterPhonic / Bider SpeechPlus (free trial no longer available) | bao3zheng4, bian4ming2, fou3ren4, jia3ru2, mei3zhou1, mu4du3, many others (via CSSML pinyin markup) | Incorrect syllables spoken (I'd have thought pinyin gives better control but it doesn't) |
| Neospeech Hui (2011-05) | 糖尿病 | 'n' of 尿 unclear |
| 奉公守法 | first syllable unclear | |
| ScanSoft (Nuance) MeiLing (also used by Nokia) | 深省 | 省 spoken as shěng instead of xǐng; no way to add a dictionary entry to override it |
| 地, 行 and many other ambiguous hanzi | Engine often gets the wrong reading (e.g. dì instead of de in many adverbs, xíng instead of háng in 十四行诗), no way to override (except sometimes by writing wrong hanzi) | |
| 邮编 | 编 pitch too low for the context | |
| 切合实际，对 | 际 in 切合实际 by itself is correctly pronounced jì, but when followed by | |
| 絶 (variant of 絕/绝), 説 (variant of 說/说) and others | completely skipped, with no indication that there is a missing character in the text | |
| 用户界面 | 界 sounds too much like 3rd tone instead of 4th tone | |
| 齁声 | Pitch falls from B to E-flat. Some drop in pitch of tone-1 at the end of a phrase is acceptable, but an augmented fifth? | |
| 人文学 | Faults on 文 (but not in 人文 by itself). Sounds better if incorrectly written as 人闻学. | |
| 撞击 | 击 sounds like a truncated neutral tone instead of tone 1 | |
| 电脑及资讯科技 | something like half a 个 is inserted before the 及 | |
| 劫难 | sounds more like jián'àn than jiénàn (it must be a coded exception to 难's usual nán pronunciation but it seems the syllable boundary is wrong) | |
| Microsoft Lili (couldn't test but heard a demo) | 才 | spoken as an unclear cǎi instead of cái (the old "MS Simplified Chinese" voice actually gets this one right but gets 央行 wrong) |
| Neospeech Lily (no longer sold separately but used by NextSpeak and ImTranslator 2011-05 without the lexicon access) | 糖尿病 | 'n' of 尿 very unclear |
| yong4chu5lai5, zhuan3lai2zhuan3qu4 (via pinyin lexicon) | Incorrectly read as yong4chu1lai5, zhuai3lai2... but OK if input as hanzi 用出来, 转来转去 | |
| chan3chu2 or 铲除 | says chu4 instead of chu2 | |
| shan4yong4 or 善用 | shen4 instead of shan4 in pinyin; "n"s clipped in hanzi | |
| li4bi4 or 利弊 | sounds like bi1bi4 | |
| you2bian1 or 邮编 | bian1 pitch too low for the context | |
| jia1de5fu1 | spoken as jiādìfū (maybe it's being treated as 加的夫, which might be right but a pinyin override shouldn't try to guess what the pinyin should have been; what if it came from 家的夫?) | |
| Loquendo Lisheng (2011) | mu4du3, mu4du4. | both words seem to end in du4 (the du3 sounds OK if it's the last thing in the sentence) |
| Apple Ting-ting (in OS 10.7) | mu4du3, mu4du4 | Both "du" sounds seem incomplete |