Adrenaline is released, the heartrate speeds up, the guts tighten up and move. This is the rush you get from loud music - it's real and it's beyond your concious control. Sounds addicting, doesn't it? .
The Chain of Transducers.
The structure of the ear forms a series of transducers to convey information about oscillations to the brain. The system converts motion in compressible fluid (the air in the outer ear) to motion in a mechanical system (the levers of the middle ear) to motion in non-compressible fluid (the fluids of the inner ear) to electrochemical impulses in the nervous system. .
The outer ear carries the oscillations to the eardrum via the ear canal, a passive acoustic filter which imparts a pre-emphasis between 1KHz and 4 KHz. In the middle ear, the vibrations of the eardrum (a vibrating elastic membrane) are conveyed to the oval window (another, more delicate, vibrating elastic membrane) via the ossicles, bones which together form a series of levers to match the acoustic impedances of the two membranes and the fluids beyond them (air being the fluid beyond the eardrum, from the ear's point of view). .
In the inner ear, the conversion takes place from hydraulic oscillations to nervous system signals. The mechanical structure of the inner ear resembles a snail-shaped tunnel through the bones of the skull, which is called the cochlea. The cochlea is filled with fluids, separated by membranes, which, when energized oscillations at the oval window, generate oscillating motion in the membrane that separates them by virtue of their different fluid densities. The relative motion between the membranes and fluids is detected by the cilia (hair cells) which wave about in the fluid and fire the neurons of the nervous system. .
The low-frequency subsystem is an analog-to-digital system which operates below approximately 1KHz, a natural consequence of Nyquist's theorem, which states that the sampling frequency required to convert analog signals to digital signals must be at least twice the highest frequency of interest.
