Fletcher-Munson curves

What are Fletcher-Munson Curves?

The Fletcher-Munson curves were created as part of extensive listening experiments. The goal was that subjective perception of volume to be understood via the audible frequency spectrum.

The Fletcher-Munson curves, also called equal loudness contours, show how loud sounds are perceived at different frequencies. These curves were developed in the 1930s by researchers Harvey Fletcher and Wilden A. Munson created. Their research showed that people's hearing reacts differently to sound at different frequencies.

The Fletcher-Munson curves show that some sounds need to be louder at low and high frequenciesto be perceived by people as equally loud compared to medium frequencies. This means that we perceive sounds less clearly at low volumes and at low or high frequencies than at moderate volumes and at medium frequencies.

Fletcher-Munson curve graphic

Where are the Fletcher-Munson curves used?

The curves have an important function in audio technology. They particularly help in the development of audio equipment and equalizers to ensure that sounds are perceived evenly across the entire frequency spectrum. This also compensates for the natural fluctuations in the hearing sensitivity of the human ear.

Hearing sensitivity at different volumes

The curves show that the sensitivity of hearing does not remain the same, but depends on the volume. At low volumes, hearing is less sensitive to low and high frequencies compared to medium frequencies. At higher volumes, the sensitivity of hearing at different frequencies becomes more similar.

Application in audio technology:

The findings of Fletcher-Munson curves are important in audio engineering. At the Recording, Mix and playback of audio content, differences in hearing sensitivity must be taken into account. audio engineers use Equalizerto correct the frequencies so that sounds are perceived as equally loud at normal volume levels, regardless of their frequency.

ISO 226.

The Fletcher-Munson curves were used as the basis for the development of the ISO 226 standard used, which standardizes the sensitivity of human hearing. This standard establishes reference sound pressure levels to ensure consistent loudness across audio devices and applications.

K and A rating.

Special filters such as K and A weighting have been developed to take into account the influence of hearing sensitivity at different volume levels. These are used in sound level measurements to achieve a similar weighting to the hearing sensitivity curves. Overall, Fletcher-Munson's curves have helped provide a basis for better device and recording design in the audio field. This ensures that the sounds are reproduced in a way that matches human perception.

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