Development of a continuous classroom signal-to-noise ratio measurement system

A successful learning experience requires children to be able to hear what the teacher is saying. To that end, children need a high signal-to-noise ratio (SNR) or speech audibility to hear the teacher under background noise, but SNR in the classrooms may not always be favourable depending on the activities taking place during a school day. We propose a classroom acoustic measurement system to monitor the time-varying SNR under interactive teaching scenarios. Emulating a child listening to the speech made by a teacher, the system utilises two consumer-grade wireless microphones, one attached to the teacher and the other located where the children would be seated. The signal received by the teacher's microphone is used as a voice activity detector to indicate the presence of the teacher's voice or noise-only audio instances. Subsequently, the children's microphone observes these instances to monitor the average classroom noise and estimate the resulting SNR. A pilot study was conducted at a primary school in Auckland, New Zealand where the SNR measurements were recorded and matched against behavioural coding of the classroom activities. Results show a reasonable agreement of the SNR to the activities performed under real-life classroom teaching scenarios.