The ears are one of the most complex and interesting systems thats human body has and the sounds we hear are actually in many different parts deflected, absorbed, and also filtered by our different body parts. It's then collected by our pinnae (the external part of or ears), whose dimensions further affect the sound on its way into ear. There, vibrations are translated into signals, which are interpreted by your brain. In the 1930s, two scientists at Bell Labs, Harvey Fletcher and Wilden A. Munson researched this process and what they discovered has changed and affected how we as humans understand the hearing process. Harvey Fletcher and Wilden Munson revealed, among other things, that the human ear is not linear, and is not capable of detecting all frequencies equally at all sound levels, which has come to be known as the Fletcher-Munson Curves, or equal loudness contours.
Harvey Fletcher and Wilden Munson discovered that our hearing is decidedly nonlinear with respect to frequency and perceived loudness, and they mapped this data at various the two researchers asked subjects to compare the loudness of sine waves at different frequencies, identifying those that they felt were comparable in loudness to a 1 kHz sine wave at a fixed level. In general, tones at the high and low ends of the audible spectrum had to be significantly more powerful than the reference tone to be perceived as the same loudness. For example, to be “as loud as” a 40 dB SPL 1 kHz tone, a 10 kHz tone needs to be about 50 dB SPL, and a 100 Hz tone must be more than 60 dB SPL. The curve actually dips between 1 kHz and 5 kHz, with its nadir between 3 kHz and 4 kHz, depending on the reference level. At lower SPLs, the variation is greater, while at higher levels, the variations are less significant, coming closest to leveling off at around 90 dB SPL. This is why wise mix and mastering engineers monitor at levels in the 85 to 90 dB SPL range, where our hearing is particularly flat. The ways in...
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