5070- Wk 4 Lecture

What are the three main parts of the ear?

Outer ear, middle ear, inner ear.

What structures are in the outer ear?

Pinna (auricle), ear canal (external auditory meatus), tympanic membrane (eardrum).

What structures are in the middle ear?

Ossicles: malleus (hammer), incus (anvil), stapes (stirrup).

What is the function of the ossicles?

Amplify pressure from tympanic membrane to cochlea; create a mechanical advantage to move fluid in the inner ear.

What does the stapes connect to?

The oval window of the cochlea.

How do sound waves travel through air?

As pressure waves (20 Hz–20,000 Hz) from moving air molecules = acoustic energy.

How does the tympanic membrane move?

Inward during compression, outward during rarefaction.

What boosts sound amplitude before it reaches the cochlea?

The pinna and ear canal (30–100 fold boost).

Why does the middle ear amplify pressure?

Because fluid is harder to move than air.

What is the cochlea?

A fluid-filled, snail-shaped structure responsible for hearing.

What is the basilar membrane?

A membrane in the cochlea that responds to different frequencies along its length (tonotopic organization).

Where do high vs. low frequencies vibrate the basilar membrane?

High = near oval window (stiff), low = farther along (flexible).

What structure sits on the basilar membrane?

The organ of Corti.

What do inner hair cells do?

Transduce sound into neural signals; send sound info to the brain.

What do outer hair cells do?

Act as cochlear amplifiers by changing shape and amplifying inner hair cell movement.

What happens when stereocilia bend?

Ion channels open, triggering neurotransmitter release and nerve impulses.

What helps with sound localization?

Time of arrival & intensity differences between ears.

Why is distance harder to perceive than direction?

Fewer cues; relies on loudness, reflections, and spectral content.

What is analog sound?

Continuous in time and amplitude; infinite detail.

What is digital sound?

Discrete in time and amplitude; made of numeric snapshots (samples).

What is ADC?

Analog-to-Digital Conversion – turns analog sound into digital numbers.

What is DAC?

Digital-to-Analog Conversion – turns digital numbers back into analog sound.

What is the Nyquist frequency?

Half the sampling rate; highest frequency that can be accurately reproduced.

What is bit resolution?

Number of amplitude levels (e.g., 16-bit = 65,536 values).

What is quantization?

Representing amplitude as a number at each sample point.

What happens if the input signal is too weak?

It uses little resolution and may have poor signal-to-noise ratio when boosted.

What is aliasing?

Misrepresentation of high frequencies as low ones due to slow sampling rate.

How do you prevent aliasing?

Use an anti-aliasing filter set at the Nyquist frequency before digitizing.