What is anatomical compression and how does it affect me?

Noise-induced hearing loss (NIHL) refers to a gradual, cumulative and preventable decline in auditory function that follows repeated exposure to loud noise. It is the leading cause of preventable hearing loss. The Occupational Safety and Health Administration’s (OSHA) definition for “material impairment of hearing” is sound over a 25 dB threshold at 1000, 2000, and 3000 Hz. We keep injecting that abbreviation “DB”, what is it?

Decibels! Sound is measured in units called decibels (dB). The higher the decibel level, the louder the sound. On the decibel scale, the level increase of 10 means that a sound is actually 10 times more intense, or powerful. But, it gets worse! The decibel (abbreviated dB) is the unit used to measure the intensity of a sound. The decibel scale is a little odd because the human ear is incredibly sensitive. Your ears can hear everything from your fingertip brushing lightly over your skin to a jet engine. In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound.On the decibel scale, the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB. A sound 1,000 times more powerful than near total silence is 30 dB. To make this short and easy, a speaker that is rated at 93DB with 1 watt of power applied to it is twice as loud as a speaker rated at 90DB with 1 watt of power applied to it. 96DB is twice as loud as 93DB and so on.

Near total silence – 0 dB
A whisper – 15 dB
Normal conversation – 60 dB (The Ideal studio mix level)
A lawnmower – 90 dB
A car horn – 110 dB
A rock concert or a jet engine – 120 dB
A gunshot or firecracker – 140 dB

Any sound above 85 dB can cause hearing loss, and the loss is related both to the power of the sound as well as the length of exposure. Anatomical compression is fancy terminology for your brain naturally compressing your ability to hear. For instance, at the beginning of a concert that is hitting you at a solid and constant 115DB will register in your perception of hearing the music at that level for approximately 15 minutes. After the 1st 15 minutes, your brain starts to naturally compress your ability to hear, it is a natural defense but DOES NOT PREVENT HEARING LOSS OR HEARING DAMAGE, it is actually a sure sign you are possibly sustaining hearing damage or at the very least temporary loss of detailed, acute hearing ability.

This is the exact reason why you never want to mix down in the recording studio at any volume level louder than a normal conversation volume level = 60 dB (The Ideal studio mix level).

Doing so stunts your ability to hear and articulate the detail of your mix. If you have ever mixed down in the studio at high volume levels and listened to the “finished product” the next day, you have noticed that the treble and or higher frequencies in the mix get higher and higher and louder and louder the further into the mix you get.

The information on Noise-induced hearing loss (NIHL) was derived from the CDC, and the “material impairment of hearing” is sound over a 25 dB threshold at 1000, 2000, and 3000 Hz was derived from OSHA, Occupational Safety and Health Administration. The tip on recording studio mix down levels being ideal at 60DB was shared with us by Doug Thiele, my recording and production professor at Old Dominion University in the 90’s.