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The transmission of sound through theear

Sound waves hitting the outer ear are both reflected (scattered) and conducted. Conducted soundwaves will travel through the ear canal and will hit the eardrum causing it to be driven inwards.

This portion of the process is measured in HRTF generation by embedded microphone. Although

the remaining process is not modelled currently, it is offered to help understand how complex thehuman auditory system is and how much work remains in the 3D sound synthesis world. The

inward force will cause the malleus and incus to push the stapes deep into the oval window of the

inner ear. The surface area of the eardrum is 30 times greater than the stapes. This causes thepressure on the oval window to be 30 times greater than the original pressure on the eardrum.

This pressure is needed for the stapes to be able to transfer the energy into the "perilymph". The

basilar membrane of the perilymph is compressed inward by the movement of the stapes. The

compression of the flexible membrane causes the round window to bulge into the middle ear.The organ of the Corti pivots in response to the movements of the basilar membrane. The action

of the organ of the Corti and the tectoral membrane sliding against each other cause the hair of

the hair cells to bend.

Near the end of the hair cells are the tips of 27,000 nerve fibers. The interconnections of these

nerve fibers and hair cells are complex and overlapping. No direct connections exist. Instead, ashairs are bent, nerve impulses are stimulated in the nerve fibers. The exact method of the

electrical impulse generation is not known, although some theories exist. The changing stiffness

of the basilar membrane from one end of the cochlea to the other creates a kind of mechanicalanalyzer of sound. High frequency sound causes the narrow basil end of the membrane to

vibrate. Medium frequencies cause the membrane in the middle cochlea to vibrate. Low

frequencies cause the whole membrane to vibrate. The cochlea is able to map frequencies onto

certain locations on the basilar membrane. The sensation of pitch is a function of the location ofthe vibration on the the basilar membrane.

Auditory nerves and thebrain

Nerve impulses are transmitted from the ear to the brain via the auditory nerves, one of the

several sensory nerves that exists in the group of nerves known as cranial nerves. The auditory

nerves connect the nerve impulses of the ears to the upper "temporal lobe" of the "cerebralcortex". Nerve impulses pass over "neurons" via an electro-chemical action. That is, the neuron

itself provides the necessary energy to propel the impulse along the nerve. The nerve impulse

does not travel as fast as a standard electrical current, but instead moves at about 3.25 to 395

feet/sec. Nerve impulses travel over many neurons on their way to the brain. Neurons worktogether by transmitting the impulses through the "axoms" to the "dendrites" of the neuron. The

dendrites of one neuron communicate to the dendrites of another by means of the "synapse". This

gap-like structure communicates by releasing a chemical transmitter substance.

Human factors involvi

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