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Google Launches Cantonese Voice Search in Hong Kong

Thursday, December 2, 2010

Posted by Posted by Yun-hsuan Sung (宋雲軒) and Martin Jansche, Google ResearchCangjie倉頡滘西州Kau Sai Chau砵典乍街Pottinger Street

Data Collection: In contrast to English, there are few existing Cantonese datasets that can be used to train a recognition system. Building a recognition system requires both audio and text data so it can recognize both the sounds and the words. For audio data, our efficient DataHound collection technique uses smartphones to record and upload large numbers of audio samples from local Cantonese-speaking volunteers. For text data, we sample from anonymized search query logs from http://www.google.com.hk to obtain the large amounts of data needed to train language models.

Chinese Word Boundaries: Chinese writing doesn’t use spaces to indicate word boundaries. To limit the size of the vocabulary for our speech recognizer and to simplify lexicon development, we use characters, rather than words, as the basic units in our system and allow multiple pronunciations for each character.

Mixing of Chinese Characters and English Words: We found that Hong Kong users mix more English into their queries than users in Mainland China and Taiwan. To build a lexicon for both Chinese characters and English words, we map English words to a sequence of Cantonese pronunciation units.

Tone Issues: Linguists disagree on the best count of the number of tones in Cantonese – some say 6, some say 7, or 9, or 10. In any case, it’s a lot. We decided to model tone-plus-vowel combinations as single units. In order to limit the complexity of the resulting model, some rarely-used tone-vowel combinations are merged into single models.

Transliteration: We found that some users use English words while others use the Cantonese transliteration (e.g.,: “Jordan” vs. “佐敦”). This makes it challenging to develop and evaluate the system, since it’s often impossible for the recognizer to distinguish between an English word and its Cantonese transliteration. During development we use a metric that simply checks whether the correct search results are returned.

Different Accents and Noisy Environment: People speak in different styles with different accents. They use our systems in a variety of environments, including offices, subways, and shopping malls. To make our system work in all these different conditions, we train it using data collected from many different volunteers in many different environments.