Design and Optimization of a Speech Recognition Front-End for Distant-Talking Control of a Music Playback Device
Table 2: Command Accuracy (%) for different commands at different SERs.
['SER (dB) params.', '−35∼−30 ASR', '−35∼−30 POLQA', '−30∼−25 ASR', '−30∼−25 POLQA', '−25∼−20 ASR', '−25∼−20 POLQA']
4.2.2 Recording of Real-World Commands We used eight subjects (male/female, native/non-native) who uttered the command list at a distance of around 1m from the microphone of the Beats Pill™ portable speaker while music was playing. We used four different music tracks in the echo path, where the starting point of the track was chosen randomly. The playback level for the experiments was set to three different levels of 95 dB SPL, 90 dB SPL, and 85 dB SPL. We estimated the range of SER for the different setups to be approximately equal to −35 to −30 dB, −30 to −25 dB, and −25 to −20 dB for the three levels, respectively. The estimation of the SERs were made possible thanks to a lavalier microphone that recorded the near-end speech. Note that the SERs in the experiments are lower than the SERs used in the simulation, which validates the generalization of the tuning methodology. The results clearly show that our proposed tuning based on ASR maximization outperforms the POLQA-based tuning. The difference in performance seems to derive from the POLQA optimization being less aggressive on noise in order to preserve speech quality. More noise in the processed files translates into worse performance of the speech recognizer and the VAD. As a reference, when our speech enhancement front end was not used, the average recognition rate was 25% over all commands (coin toss) in the lowest SER setup.