Sound Level Calibration of a Kiosk for Psychoacoustic Testing

This document details the calibration process of kiosks for psychoacoustic testing. NASA developed a remote psychoacoustic testing capability to enable participation of geographically diverse members of the public using their personal audio equipment. This capability is used in the Varied Advanced Air Mobility (AAM) Noise and Geographic Area Response Difference (VANGARD) test. When people use different audio equipment, it creates uncertainty in test results. Calibrated kiosks with known playback levels can be used with a small control group of test subjects to address this uncertainty. The current kiosk design consists of a Microsoft Surface Go 3 tablet computer and Sennheiser HD 280 headphones. Two options are available for digital-to-analog conversion of sound stimuli: the sound card in the Surface Go 3 computer or a DragonFly USB digital-to-analog converter (DAC) unit. The kiosk calibration process described here is performed using a manikin head with in-ear microphones. A pink noise signal is used to determine the spectral response, sound level as a function of volume setting, and measurement variability. VANGARD test stimuli are played through the kiosk and measured with the manikin head to determine the tablet computer volume setting needed to play back stimuli at their intended sound level. The calibration process determined that for the VANGARD test a volume setting of 47 is appropriate when using the kiosk with the onboard sound card and 21 with the DragonFly DAC. These settings ensure that most sounds play within ±2 dB of the intended A-weighted sound exposure level (ASEL) and maximum sound level (LAmax).