Guidelines for Selecting Microphones for Human Voice Production Research

What is it about?

Purpose This tutorial addresses fundamental characteristics of microphones (frequency response, frequency range, dynamic range, and directionality), which are important for accurate measurements of voice and speech. Method Technical and voice literature was reviewed and analyzed. The following recommendations on desirable microphone characteristics were formulated: The frequency response of microphones should be flat (i.e., variation of less than 2 dB) within the frequency range between the lowest expected fundamental frequency of voice and the highest spectral component of interest. The equivalent noise level of the microphones is recommended to be at least 15 dB lower than the sound level of the softest phonations. The upper limit of the dynamic range of the microphone should be above the sound level of the loudest phonations. Directional microphones should be placed at the distance that corresponds to their maximally flat frequency response, to avoid the proximity effect; otherwise, they will be unsuitable for spectral and level measurements. Numerical values for these recommendations were derived for the microphone distances of 30 cm and 5 cm. Conclusions The recommendations, while preliminary and in need of further numerical justification, should provide the basis for better accuracy and repeatability of studies on voice and speech production in the future. Note More detailed analysis done in a subsequent paper (Sramkova H, Granqvist S, Herbst CT, & Svec JG: The softest sound levels of human voice in normal subjects. Journal of the Acoustical Society of America, 137(1), 407-418, 2015) adjusted one of the recommendations as follows: "The equivalent noise level of the microphones is recommended to be at least 10 dB lower than the sound level of the softest phonations."

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Why is it important?

When creating a voice and speech laboratory and preparing measurements, one faces the question “Which microphone should be used?” Although microphones present basic means for capturing voice signals, there has not been enough information published on which microphones are or are not suitable for voice measurements. While there have been attempts to provide recommendations for the choice of microphones, so far there has been an insufficient explanation of the principles on which the recommendations should be based. This lack of information has led to a situation in which studies have been published with improperly chosen microphones, and the reported results have contained inherent errors. The purpose of this tutorial is therefore to provide guidelines for selecting a microphone that is suitable for measurement of voice and speech. Specifications provided by the manufacturer are reviewed and put into relation with the characteristics of voice and speech. Finally, recommendations are formulated that can be used for selecting the proper microphone for voice and speech research.

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