"When it's feasible to use audio, there is considerable evidence that presenting words in audio rather than on-screen text can result in significant learning gains." (2011, Richard E. Mayer and Ruth C. Clark)

"Sounds, such as the noise of certain machinery, or the background hum of daily life, have an associative as well as a pure meaning, which can be used to evoke images or ideas relevant to the main substance of what is being taught. There are, in other words, instances where audio is essential for efficiently mediating certain kinds of information." (1984, Nicola Durbridge at Open University)