If you are preparing to record sound in a studio, you need to understand the basics of human hearing. The ear picks up sound vibrations and translates them into a form that your brain can understand. To hear sound, you ear performs the following functions:
The pinna, the outer part of your ear, catches the sound waves. The structure of the outer ear has a number of curves and is pointed forward. The way the sound reflects off of the pinna helps you hear where the sound is coming from.
Next the sound waves travel down the ear canal and vibrate the eardrum. The eardrum is a stretched drum-like membrane where the sound waves are changed into mechanical vibrations.
These vibrations are transferred to the inner ear by way of three of the tiniest bones in the body; the hammer, anvil and stirrup. These bones act both as an amplifier and a limiting device.
Then the vibrations are applied to a tubular, fluid-filled, shell-like device called a cochlea. The cochlea takes these vibrations caused by the sound wave and translates them into electrical information the brain can recognize as distinct sound.
The Threshold of Hearing refers to the minimum sound pressure-level, or SPL, that produces the fact of sound in most people. It is equal to a 0.00002 microbar, or 0dB SPL. When you understand that one microbar equals one-millionth of normal atmospheric pressure, then you begin to understand how sensitive the human ear is.
The Threshold of Feeling is the SPL that causes discomfort in the listener 50% of the time. It occurs at a level of 118 dB, between the frequencies of 200 Hz and 10kHz.
The Threshold of Pain is the SPL that causes pain in a listener 50% of the time and corresponds to an SPL of 140 dB in the frequency between 200 Hz and 10 kHz.
Psycho-acoustics refers to the how and why the brain interprets a sound in a certain way. The primary device in psycho-acoustics is the human brain, and the way the brain works is still elusive in science today.
Understanding human ear sensitivity helps you realize how important it is to take care and protect yourself, and others, from long-term exposure to extreme sound levels in the recording studio.