Originally Posted by AudioTrack
. . .it is important to understand that sound levels are heard by humans on a logarithmic scale.
Yes, we do hear on a logarithmic scale but that’s half the story. The other half is that we hear on a highly non-linear basis as a function of frequency. Some of the first research on how the ear hears different frequencies at different levels was done by Fletcher and Munson in 1933; brilliant work and the design of our auditory system is truly astonishing.

A simplified description of the several transduction steps begins with the physics of a pressure wave. The acoustic energy is converted to mechanical energy in the eardrum, which causes the fluid-filled cochlea to vibrate. This fluid motion causes the hair sensory cells to bend, causing electrical signals to be generated which are fed to the auditory cortex which processes the signals allowing us to perceive, understand and interpret the information.

I’m not aware of a single unified equation that encapsulates both the logarithmic aspect and the frequency-based equal loudness curves. If I had such an equation, I might be able to produce a 3-D surface plot showing the complete 2 input and 1 output relation. If no such relation exists (which would surprise me) I’m guessing that hearing aid designers use nonlinear regression or table look-up methods. Perhaps someone that wears them or has worked in that industry may know more about how they do their DSP in this regard.

Attached Files (Click to download or enlarge) (Only available when you are logged in)
Perceived Hearing.jpg (67.57 KB, 56 downloads)
https://soundcloud.com/user-646279677
BiaB 2025 Windows
For me there’s no better place in the band than to have one leg in the harmony world and the other in the percussive. Thank you Paul Tutmarc and Leo Fender.