Filtered sound – The impact of aerosol filters on the sound of brass instruments

Abstract

COVID-19 is transmitted primarily via respiratory droplets and aerosols. Early in the pandemic, concerns were raised that wind instruments could increase the risk of infection. Therefore, several studies investigated the droplet and aerosol emissions from wind instruments. While wind instruments don’t emit droplets, they still produce aerosols. As a countermeasure, aerosol filters for brass instruments were proposed. This study investigates whether such filters affect the timbre and radiation patterns of the filtered instrument. Four brass and one woodwind instrument (flute, French horn, trombone, trumpet, tuba) were recorded in three registers (low/mid/high), at two dynamic levels (p/f), and in three filter conditions (0/1/2 layers). The instruments were played by musicians and recorded on stage to approximate concert conditions. The radiation patterns were captured with an acoustic camera. Subjects rated the timbre, intonation, and articulation of the recorded sounds. The ratings were compared using a paired t-test. Low-level audio features were extracted and analyzed to identify the acoustic properties affected by the filter. One-layered filters had no influence on the subjective ratings. With two layers, the difference from the zero-filter condition was significant. Overall, the impact on intonation was considerably greater than on timbre. Differences in the radiation patterns were not found.