Playback level calibration by hand rubbing for remote listening test

Playback level calibration is an important procedure in listening tests. However, this is a challenging task in remote listening tests, which have become more popular nowadays. A convenient method, which has been used in an online hearing test, is to adjust the playback level so that the perceived loudness of a hand rubbing recording matches the subject's own hand rubbing. However, the reliability of this method has not been formally investigated. This paper firstly proposes a procedure for creating a reference hand rubbing recording and calibrating the stimulus level by the experimenter and the subject. The paper then describes an experiment that was conducted to investigate the inter-subject consistency of the sound pressure levels (SPLs) of hand rubbing made by fifteen subjects. It was found that the mean SPLs (LAeq) and 95% confidence intervals for three rubbing intensities Hard, Medium and Soft were 54.5 dB (±2.4 dB), 46.8 dB (±2.8 dB), and 39.8 dB (±3.2 dB), respectively. This seems to imply that the inter-subject variability of hand rubbing SPLs would be small enough to allow for reasonably consistent playback level settings across different people in a remote listening test environment.