Air-Borne and Tissue-Borne Sensitivities of Bioacoustic Sensors Used on the Skin Surface

Abstract

Measurements of body sounds on the skin surface have been widely used in the medical field and continue to be a topic of current research, ranging from the diagnosis of respiratory and cardiovascular diseases to the monitoring of voice dosimetry. These measurements are typically made using light-weight accelerometers and/or air-coupled microphones attached to the skin. Although normally neglected, air-borne sounds generated by the subject or other sources of background noise can easily corrupt such recordings, which is particularly critical in the recording of voiced sounds on the skin surface. In this study, the sensitivity of commonly used bioacoustic sensors to air-borne sounds was evaluated and compared with their sensitivity to tissue-borne body sounds. To delineate the sensitivity to each pathway, the sensors were first tested in vitro and then on human subjects. The results indicated that, in general, the air-borne sensitivity is sufficiently high to significantly corrupt body sound signals. In addition, the air-borne and tissue-borne sensitivities can be used to discriminate between these components. Although the study is focused on the evaluation of voiced sounds on the skin surface, an extension of the proposed methods to other bioacoustic applications is discussed.

Observation and analysis of in vivo vocal fold tissue instabilities produced by nonlinear source-filter coupling: A case study

“…The accelerometer was preamplified with a custom-made preamplifier (Cheyne et al, 2003) and was attached to the suprasternal notch ($5 cm below the glottis) to obtain indirect estimates of the subglottal pressure. This accelerometer at this location was essentially unaffected by sound radiated from the subject's mouth (air-borne corrupting components), even with loud vocal intention (Zañartu et al, 2009). …”

Accuracy of Self-Reported Estimates of Daily Voice Use in Adults With Normal and Disordered Voices

“…Speaking time is typically estimated with ambulatory monitors that use microphones to capture the acoustic speech signal that includes voiced, unvoiced, and silence segments (Airo, Olkinuora, & Sala, 2000;Buekers et al, 1995;Sala et al, 2002;Södersten, Granqvist, Hammarberg, & Szabo, 2002). Phonation time has been studied in ambulatory settings using both neck-placed contact microphones (Ohlsson et al, 1989;Ryu, Komiyama, Kannae, & Watanabe, 1983;Szabo, Hammarberg, Håkansson, & Södersten, 2001;Watanabe et al, 1987;Watanabe, Komiyama, Ryu, & Kannae, 1984) and accelerometers (Cheyne, Hanson, Genereux, Stevens, & Hillman, 2003;Hillman, Heaton, Masaki, Zeitels, & Cheyne, 2006;Mehta, Zañartu, Feng, Cheyne, & Hillman, 2012;Popolo, Švec, & Titze, 2005;Titze et al, 2007) that respond primarily to neck skin vibration generated during phonation, with little activity during unvoiced speech sounds (Zañartu et al, 2009).…”

A portable analyzer for vocal signal monitoring

“…An important advantage of the accelerometer consists in its high Tissue-borne to Air-borne Ratio (TAR) with respect to air-coupled microphones [26], that makes negligible the effects of air-borne transmitted sounds generated by the talker or due to the background noise. One of the main reasons the electret microphone is investigated as an alternative to the accelerometer is its expected larger bandwidth, as also reported in [27].…”