A quantitative assessment of the importance of tone in mandarin speech recognition

How important is tone to Mandarin speech recognition? Because contextual information can resolve some lexical ambiguities, the question has been raised as to whether a strong language model obviates the need for explicit tone modeling. This letter addresses that question by evaluating the effect of tone information on word perplexity under different conditions, including knowledge of the correct tone sequence, perfect acoustic information, and imperfect syllable and tone information. Results show that conditioning on tone information can reduce word uncertainty in conversational speech by 11%-20%, depending on the accuracy of syllable and tone recognition.