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Purpose: Sound pressure level (SPL) measurement of voice and speech is often considered a trivial matter, but the measured levels are often reported incorrectly or incompletely, making them difficult to compare among various studies. This article aims at explaining the fundamental principles behind these measurements and providing guidelines to improve their accuracy and reproducibility.
Method: Basic information is put together from standards, technical, voice and speech literature, and practical experience of the authors and is explained for nontechnical readers.
Results: Variation of sPl with distance, sound level meters and their accuracy, frequency and time weightings, and background noise topics are reviewed. Several calibration procedures for SPL measurements are described for stand-mounted and head-mounted microphones.
Conclusions: SPL of voice and speech should be reported together with the mouth-to-microphone distance so that the levels can be related to vocal power. Sound level measurement settings (i.e., frequency weighting and time weighting/averaging) should always be specified. Classified sound level meters should be used to assure measurement accuracy. Head-mounted microphones placed at the proximity of the mouth improve signal-to-noise ratio and can be taken advantage of for voice SPL measurements when calibrated. Background noise levels should be reported besides the sound levels of voice and speech.
(ProQuest: ... denotes formulae omitted.)
Certain topics of voice and speech production have become so much a part of common knowledge that they are considered obvious. An example of such topic is voice intensity or, more accurately, the sound pressure level (SPL) of voice, which is covered in most textbooks devoted to voice and speech production. Measurements of SPL are offered by most voice and speech analysis packages. However, it is the experience of the authors that SPL measurements are often done inadequately and the reported values are meaningless, even if done with sophisticated software or hardware. An example could be taken from the popular Guinness World Records on the loudest human vocalization stating: "Classroom assistant Jill Drake (UK) had a scream that reached 129 dBA when measured at the Halloween festivities held in the Millennium Dome, London, UK in October 2000" (Guiness World Records, 2017). Unfortunately, this statement fails to provide crucial pieces of information, particularly at which distance the measurement was done and what time weighting or time averaging was used...