Towards Minimally Invasive Velar State Detection in Normal and Silent Speech

We present a portable minimally invasive system to determine the state of the velum (raised or lowered) at a sampling rate of 40 Hz that works both during normal and silent speech. The system consists of a small capsule containing a miniature loudspeaker and a miniature microphone. The capsule is inserted into one nostril by about 10 mm. The loudspeaker emits chirps with a power band from 12–24 kHz into the nostril and the microphone records the signal reflected from the nasal cavity. The chirp response differs between raised and lowered velar positions, because the velar position determines the shape of the nasal cavity in the posterior part and hence its acoustic behaviour. Reference chirp responses for raised and lowered velar positions in combination with a spectral distance measure are used to infer the state of the velum. Here we discuss critical design aspects of the system and outline future improvements. Possible applications of the device include the detection of the velar state during silent speech recognition, medical assessment of velar mobility and speech production research.