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near-field_measurements_of_the_human_voice_using_a_microphone_array_preliminary_study [2014/03/18 20:01] (current)
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 +Hana Šrámková, Efren Fernandéz-Grande, Jonas Brunskog, Jan G. Švec (The Czech Republic, Denmark)
 +**Near-field measurements of the human voice using a microphone array – preliminary study**
 +Miniature head-mounted microphones have become very popular for capturing voice and speech signals. Although widely used, it is not clear how accurate the measurement results obtained with these microphones are. They are typically placed at a 1-5 cm distance from the mouth, often close to the cheek. All these placements are in the near field of the voice source, and therefore the recorded signals may be considerably influenced by the exact position of the microphone. The goal of this study is to examine how accurately the sound pressure level and spectrum of the voice can be measured with a head-mounted microphone, and how changes in the microphone placement can influence the measurements. 
 +1 untrained vocally healthy female took part in the study. The recordings were performed in the anechoic chamber at the Department of Electrical Engineering, Technical University of Denmark. For investigation of the sound field, a hand-held microphone array (Brüel&Kjaer, 8x8 microphones, 3 cm spacing) and a reference microphone (Brüel&Kjaer type 4192) were used. Measurements with the array were done at three different angles – 0°, 45° and 90° and at several distances (the distance of the middle microphone from the mouth according to closest possible position of the array). Position of the head was fixed by a special holder. Sustained phonation of Czech vowel [a:] was recorded at all of the distances and angles. Recordings and analyses were done using the program PULSE (Brüel&Kjaer) and Matlab. 
 +The preliminary results show that the sound levels in the near field change rather smoothly in the frequency range of 100-1000 Hz. At 3cm in front of the mouth, the change of the microphone position to the side at the level of the mouth was found to cause the difference of ca. 1dB/cm up to the distance of ca. 10 cm to the side. The results suggest that the microphone positioning in the near field may allow reasonably accurate measurements of voice sound level and spectrum.
 +The research has been supported in Czech Republic by the European Social Fund Projects CZ.1.07/2.4.00/17.0009 and CZ.1.07/2.3.00/20.0057 and by the Palacky University student’s project PrF_2013_017. Special thanks are expressed to Woo-Keun Song and Brüel & Kjaer for their help with the equipment and data analysis. 
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