Harmonic cancellation: eliminating unwanted noise

Have you ever had the impression, during a noisy meal, that you had to strain your ears to follow the conversation properly? In fact, in this type of social situation, the auditory mechanism at work appears to suppress unwanted sounds rather than amplifying the voice you are trying to hear. But when two voices have the same frequency, the brain has trouble distinguishing between them. These are the findings of studies conducted by Mickael Deroche, a psychology professor at Concordia University.

The researcher investigated this suppression of interfering sounds, called harmonic cancellation, through a series of laboratory experiments. In a first experiment designed to prove the existence of the phenomenon, a whistling sound of a specific frequency was played to young adult participants with no hearing problems. The researcher then observed that another sound emitted at the same time and having harmonics of the same frequency masked the whistling sound. Harmonics are the multiple frequencies emitted by the vocal cords that give each voice its texture and particular sound.

To illustrate harmonic cancellation, imagine a large “comb” in the auditory system, each tooth of which cancels a certain harmonic frequency. If a sound falls between two teeth of the comb, the auditory system can easily detect it, but if it lines up with one of the teeth, harmonic cancellation interferes with the detection of that sound.

However, every individual’s “comb” is different and some of them are coarser, meaning that they tend to comb too wide. The researcher discovered that people with a developed musical ear who were better able to detect small differences in pitch had a finer “comb” and could thus more finely mask competing sounds to better hear a voice in a noisy environment.

Given the aging population and the increasing popularity of listening to loud music through headphones, we are likely to see a worrying increase in hearing loss in the coming years. Mickael Deroche’s research could help mitigate the consequences of hearing loss by helping to design more effective hearing aids that could make it easier to listen during complex conversation situations.

The results of this study have not yet been published.