Frequency characteristics of several non-audible murmur (NAM) microphones

摘要

A non-audible murmur (NAM) is a very weak speechsound produced without vocal vibration that can be detectedusing a specially designed sensor: a NAM microphone [1,2].Nakajima invented the NAM microphone; several types ofNAM microphone have been developed since then [2].Because NAM sounds are not heard, the NAM is applicablefor telephone systems that require privacy. Because air-conducted the noise sounds are not mixed with sounds pickedup by the NAM microphone, the device can eliminate thenoise problems of automatic speech recognition systems [3].The NAM microphone can also revive the speech communi-cation capabilities of people with vocal cord problems causedby cancer of the larynx, nerve disorders, and muscle diseases[4]. However, the frequency characteristics and sensitivities ofNAM microphones have yet to be revealed. This paper reportsthe frequency characteristics and sensitivities of five differenttypes of NAM microphones.