Module 2 Sound and Hearing Mechanism

What is sound?

Sound is a common type of energy that occurs as a result of pressure waves that emanate from some force being applied to a sound source.

How does sound form?

From the compression of molecules in the medium through which it is traveling.

Groups of molecules are compressed which in turn

compress adjacent groups of molecules. This results in waves of pressure that emanate from the source

What are the requirements for sound?

source of vibratory energy and a medium that has mass and is elastic

Particle Motion

particles bump into each other transferring energy from one another

The magnitude of a sound is described as its

intensity

Intensity is related to the

perception of loudness

The higher the magnitude of the compression wave

the higher is the intensity of the signal

Wave form properties

The range of intensity of sound that is audible to humans is

quite large

The pressure level of a sound that is just barely audible is approximately

20 micro pascals

The pressure level of a sound that is so intense that it is painful is

200,000,000 micro pascals

Because this range is so large

a unit of measurement called the decibel is used

Intensity is described as

the logarithm of a measured pressure to a reference pressure

The unit of measure to describe intensity is called a

bel

Which person was bel named after?

Alexander Graham Bell

1 bel , 2 bels =

10 decibels 20 decibels

Intensity is most often expressed in

decibels (db) sound pressure level (db SPL)

db SPL Formula

db SPL =10 log

(pressure / reference pressure)²

db SPL = 2 × 10 log

(pressure / reference pressure)

db SPL = 20 log

(pressure/ reference pressure)

Important point 1 of db SPL visual

The logarithm idea is a way of reducing the range of pressure levels to a tractable one. By using this approach pressure that vary from 1:1 to a hundred million: 1 can be expressed as varying from 0 to 140 db.

Important point #2 db SPL visual

decibels are expressed as a ratio of a measured pressure to a reference pressure. This means that 0 db does not mean no sound. it simply means that the measured pressure is equal to the reference pressure as follow:

Frequency is the speed of

vibration

Frequency is related to the perception of

pitch

The higher the speed of vibration of the compression wave

the higher is the frequency of the signal

Frequency is usually expressed in

cycles per second or hertz

human hearing in young adults ranges from

20 to 20,000 hz

For audiometric purposes

frequency is not expressed in a linear form, rather it is partitioned into octave intervals

An octave

is simply twice the frequency of a given frequency

Phase

is the location at any point in time in the displacement of an air molecule during simple harmonic motion

Phase is expressed in degrees of a

circle

Sinusoidal motion

circular motion and the back and forth movement of an air molecule

Sinusoid

is a periodic wave in that it repeats itself at regular intervals over time

Waves that are not sinusoidal are considered

complex as they are composed of more than one sinusoid that differ in amplitude, frequency, and or phase

Sounds in nature are usually complex

and they are rarely sufficiently described on the basis of the characteristics of a single frequency

For complex sounds

the interaction of intensity and frequency is referred to as the sounds spectrum.

single wave

complex wave

Sensitivity

is defined as the capacity of a sense organ to detect a stimulus

absolute sensitivity

pertains to the capacity of the auditory system to detect faint sound

differential sensitivity

pertains to the capacity of the auditory system to detect difference of changes in intensity, frequency, or some other dimension of a sound.

Hearing sensitivity

most commonly refers to absolute sensitivity to faint sound

hearing acuity

most accurately refers to the differential sensitivity usually to the ability to detect differences in signals in the frequency domain.

threshold

is the level at which a stimulus or change in stimulus is just sufficient to produce a sensation or an effect

In hearing absolute threshold

is the threshold of audibility or the lowest intensity level at which an acoustic signal can be detected

Threshold is usually defined as the level at which a sounf can be heard

50% of the times that it is presented

Auditory response area

Audiometric Zero

The conversion from sound pressure level to hearing level to an audiogram

Differential threshold

also called difference limen is the smallest difference that can be detected between two signals that vary in some physical dimension

HEaring acuity

most accurately refers to the differential sensitivity, usually to the ability to detect difference in signals in the frequency domain

Intensity difference limen

Generalized drawing of the relationship between intensity of a signal and difference limen for intensity. The term sensation level refers to the number of decibels above a person hearing threshold.

Frequency difference limen

Generalized drawing of the relationship between frequency of a signal and the difference limen of frequency

Threshold of hearing sensitivity

is just one way to describe hearing ability. It can also be described in terms of suprathreshold hearing perception

Loudness

refers to the perception that occurs at different sound intensities. Low intensity sounds are perceived as soft sounds, while high intensity sounds are perceived as loud sounds. As intensity increases, so too does the perception of loudness

Pitch

refers to the perception that occurs different sound frequency. Low frequency sounds are perceived as low in pitch, and high frequency sounds are high in pitch. As frequency increases so does the perception of pitch.

What is a spectrogram?

visually represents sound frequencies over time using color or brightness for amplitude

Axes and Dimensions

Time is horizontal frequency is vertical and amplitude is shown by brightness or color.

Applications of spectrograms

used in linguistics audiology and music technology to analyze pitch loudness and timbre.

Educational importance

spectrograms help students visualize sounds concepts making acoustic theour easier to understand.

Time axis representation

The horizontal axis of a spectrogram represents time, showing how sounds evolve moment by moment.

Frequency axis representation

the vertical axis depicts frequency, with low frequencies at the bottom and high frequencies at the top.

Color indicates loudness

color brightness in a spectrogram reflects loudness, with brighter colors indicating louder sounds

Complex sound patterns

complex sounds show multiple frequency bands simultaneously, revealing pitch changes and harmonic structures

Speech pattern analysis

spectrograms help linguistics study vowel formats and consonants transitions to understand the speech details.

Clinical Voice diagnosis

speech language pathologists and audiologists use spectrograms to diagnose voice disorders and asses auditory processing abilities respectively.

Music sound visualization

musicians use spectrograms to visualize harmonic content and itmbre in comples musical signals

Therapy and intervention support

spectrograms support monitoring therapy progress and designing personalized interventions for speech anomalies.

Speech Acoustic insights

spectrograms reveal detailed speech acoustics helping slps evaluate voice quality pitch and articulation effectively

Clinical applications

slp use spectrograms in voice therapy phonological assessments and auditory evaluations to track and diagnose speech issues.

Professional development

mastering spectrogram skills enhances research capabilities and supports evidence based clinical documentation and treatments