Speech recognition system and method for variable noise environment

摘要

An automotive vehicle speech recognition system sets a recording-mode reference threshold level to be lower than a recognition-mode reference threshold level. Therefore, a spoken instruction supplied to the system in a low voice while the vehicle is parked in a quiet place during a record mode can be correlated with an instruction uttered in a loud voice during a recognition mode while the vehicle is running in a noisy environment. During the record and recognition modes reference threshold signals derived by smoothing a spoken instruction are multiplied by two different factors such that the reference threshold in the recognition mode has a greater multiplication factor than the reference threshold in the record mode. While the driver is uttering a command a first smoothed version of the utterance power spectrum is compared with a fixed reference threshold level, set to the value of a second smoothed version of the utterance power spectrum at the time the utterance began. While no command is being uttered the reference threshold varies in accordance with the second smoothed version. The first smoothed version includes higher frequency components than the second smoothed version.