In an experiment designed to determine the effects of compression on hearing, scientists had guinea pigs listen to Adele for a week. The results were extraordinary.
Sounds processed by a compressor are more harmful to hearing than unprocessed sounds. Researchers at the Pasteur Institute in Paris came to this conclusion after studying the effects of different signals on guinea pigs while using Adele's music as an example.
As part of the study, the scientists investigated how the brain perceives compressed and uncompressed music. The authors noted from the beginning of their work that processed and unprocessed compressor compositions differ greatly in volume and obviously affect hearing differently. The main objective was not to confirm the harmful effects of loud sounds on the body but rather to examine their effects in more detail.
The study showed that quieter music with pronounced silences and pauses between sounds gives the brain the opportunity to "comprehend what has been heard" and "understand what has just happened." In doing so, the brain "prepares" the body for the occurrence of a large number of sounds, creating a kind of defense for the nervous system. Conversely, louder music, especially that abundantly processed with a compressor to achieve higher volume, overloads the brain with information, tiring the listener. The brain constantly works with loud sounds, straining the nervous system.
To study the effects of different types of sound processing on hearing and the body, scientists gathered two groups of guinea pigs. Both groups were given the same music — Adele's "I Miss You" was chosen as the test track. The first group was given an uncompressed version of the song, and the second group was given a compressed version. Both groups listened to the track at the same volume level of 102 dB.
After the experiment, the researchers examined the guinea pigs' hearing apparatus. Both groups suffered inner ear damage, resulting in mild, temporary disruption of the auditory apparatus. At the same time, the stirrup muscle of the middle ear (a 1 mm muscle present in the auditory apparatus of many mammals, including humans, that protects the ear from loud sounds) was more damaged in the group that listened to the compressed version than in the group that listened to the uncompressed version. This occurred despite both groups listening to the song at the same volume.
The hearing of the animals that listened to Adele without compression fully recovered within a day after the experiment. The experiment was repeated seven times to verify the results, and the time it took for the subjects' hearing to recover did not change. At the same time, scientists note that the stirrup muscle, damaged by a very loud sound, restored its original state within a day.
Meanwhile, the guinea pigs in the second group, who listened to the compressed version of the music, were unable to regain their hearing. Their reflexes dulled, and the stirrup muscle had only partially recovered one week after the experiment.
Paul Awan, the study's leader, explained that constant exposure to compressed music overloads the nerve endings involved in processing auditory signals, directly affecting their ability to recover at rest. Awan noted that this study revealed that hearing is affected not only by the volume of the signal itself but also by its constant dynamics. The more detrimental influence of constant dynamics remains to be seen. In the future, Awan plans to determine what amount of compression is harmless to hearing and whether full recovery of the ear muscles is possible after prolonged exposure to a compressed signal.
The French scientists' study results were published in the peer-reviewed scientific journal Hearing Research.
