The Potential of Speech as the Calibration Sound for Level Calibration of Non-Laboratory Listening Test Setups

The pandemic of COVID-19 and the resulting countermeasures have made it difficult or impossible to perform listening tests in controlled laboratory environments. This paper examines the possibility of using speech for level calibration of sound reproduction systems used in listening tests performed in non-laboratory conditions, i.e., when such tests are distributed through the means of electronic communication and performed in a home environment. Moreover, a larger pool of potential test subjects can be reached in this manner. The perception of what the “normal” level of reproduced speech should be was examined through a listening experiment by letting the listeners set the level of reproduced speech samples as they saw fit, depending on the used sound reproduction system, the (non)existence of visual stimulus, and the voice of the speaker. The results show that the perception of normal speech level is highly individual when it comes to setting that level by listening to reproduced speech. The interindividual differences between the subjects are considerably larger than the impact of the three main effects. The understanding of what the “normal” level of read speech should be was examined experimentally as well by asking the subjects to read a paragraph of text, depending on the visual stimulus. The results show that the “normal” level of read speech is reasonably consistent and averages at 55 dBA at a normal conversational distance of 1 m, in a room with room acoustics conditions typical for home environment and low background noise, and with the visual stimulus that mimics the interlocutor put within the personal space of the reader. A preliminary proposal is given of a level calibration method for non-laboratory listening experiments based on these results, and some of its aspects that require further research are discussed.