Sound Wave Characteristics

• Air molecules are always in motion in random patterns
• Air is composed of nitrogen, oxygen, and hydrogen

Sound Wave Travel

• Sound waves are created when a particle is vibrated
• The vibration causes the surrounding air molecules to collide and create changes in pressure.
• The change in pressure creates a wave that travels from molecule to molecule

Longitudinal Propagation

• Displaced particles move parallel to the wave's direction of travel

Transverse Propagation

• Displaced particles move perpendicularly relative to the wave's direction of travel

Pressure

• Pressure refers to the total force exerted on a surface in a perpendicular direction

CGS System

• The unit of force is dyne
• The area unit is in squared cm
• 1 dyne/cm2 equals 1 microbar, primarily used for dB SPL

MKS system

• The force unit use is Newton
• Area is measured in squared meters
• 1 newton/m2 equals 1 pascal, typically used for dB IL

Pascal

• Pascal is too large for Speech, Language, and Hearing Sciences (SLHS)
• Micropascal (µPa) is a more practical unit
• 1 µPa equals one-millionth of a pascal

Subglottal Pressure Measurement

• Measurements are taken through water displacement
• 100 pascals is equivalent to 1 cm H2O

Speech Production Pressure

• Speech production needs 400-800 Pascals or 4-8 cm H2O

Minimum Driving Pressure

• Pressure needed to blow open the vocal folds is 3-6 cm H2O

Air Pressure Equalization

• Air flows from areas of high pressure to areas of low pressure
• Differences in pressure are what drive airflow

Laminar Flow

• Molecules move in a parallel manner at the same speed
• It creates a smooth airflow which helps create vowel sounds

Turbulent Flow

• Obstacles disrupt the flow, leading to less regular movement
• Produces random variations in pressure
• Turbulent flow is needed to produce fricatives such as /s, z, ʃ, v/ etc.

Elasticity

• It is the tendency of an object to return to its original size, shape, and location

Inertia

• Matter will remain at rest or continue in a fixed direction unless acted upon by an external force

Amplitude

• The measurement of the maximum distance a molecule is displaced from its resting position

Damping

• Damping refers to a reduction of amplitude and the energy of a sound

Ambient Pressure

• Resting pressure
• It is, the external force needed to disrupt air molecules from their random pattern of movement

Compression

• Increased pressure within a medium brings molecules closer together

Rarefaction

• Decreased pressure within a medium causes molecules to separate

Frequency Formula

• Frequency = cycles per second (Hz)
• F= 1/P : Frequency is equal to 1 divided by period (P)
• F↑, P↓: As Frequency increases, Period decreases

Period

• Amount of time it takes to complete a cycle

Incident Wave

• A sound wave that travels a certain distance, then hits an object
• It can then be transmitted, absorbed, or reflected

Constructive Interference

• Incident and reflected waves are in phase
• Forms a new wave with greater amplitude

Destructive Interference

• Waves are 180 degrees out of phase and create no wave

Four Attributes of Sound

• Frequency, pitch
• Amplitude, Loudness
• Period
• Phase

Frequency dependency

• Frequency is reliant on length, mass and tension

Frequency and Length

• Longer vibrating objects produce slower vibrations

Frequency and Mass

• Increased object mass results in slower vibration

Frequency and Tension

• Decreased tension also leads to slower vibration

Instantaneous Amplitude

• Displacement from any point on a waveform

Peak to Peak Amplitude

• Displacement from positive max displacement to negative max displacement

Peak Amplitude

• Maximum displacement in one direction

Root Mean Square (RMS) Amp

• Gives overall value of a sine wave

Intensity

• Intensity refers to energy distributed across a Surface Area
• Measured in Watts/m^2

Inverse Square Law

• Intensity decreases at a 4-fold rate when distance from the sound source is doubled
• Results in a loss of ≈ 6 dB per doubling distance

Decibel Intensity Level (dB IL)

• dB IL = 10 log (I1/I0)
• I0 is considered the threshold of hearing
• I0 = 10^-12 W/m^2

Intensity Level Changes

• Doubling intensity ≈ +3 dB
• Halving intensity ≈ -3 dB

Decibel Sound Pressure Level

• dB SPL = 20 log (P1/P0)
• P0 = threshold of hearing
• P0 = 0.0002 dyne/cm^2

Pressure Level Changes

• Doubling pressure ≈ +6 dB
• Halving pressure ≈ -6 dB

Simple Waveform Characteristics

• Single frequency, pure tone

Complex Waveform Characteristics

• More than one frequency
• Sum of multiple simple waves

Periodic complex waveform

• Frequencies repeat at equal intervals

Aperiodic complex waveform

• Cycles do not repeat at equal time intervals
• Can be continuous (prolonged noise period) or transient (brief noise period)

Fundamental Frequency (F0)

• Lowest frequency in a complex periodic wave

Waveform and Sound

• Amplitudes over time
• Displayed visually

Spectrum and Sound

• Displays amplitude over frequency
• Sound displayed at one time
• F0 (harmonics) shown by a line

Spectrum Envelope

• Spectrum envelope use periodic waves

Spectrogram

• Shows time, frequency, and amplitude

Resonant Frequency

• Objects vibrate more intensely at their resonant frequency
• Determined by characteristics of an object

Resonators

• Filter frequencies near the resonant frequency, RF
• Dampen frequencies away from RF

Resonance Curves

• Transfer functions display the frequency response of a resonator

Low Pass Filter

• Low frequencies pass through

High Pass Filter

• High frequencies pass through

Band-Pass Filters

• Allow a certain band of frequencies through

Roll-Off Frequency

• Attenuation rate of a filter over a frequency range

Octave

• For each octave doubled, the frequency also doubles

Wavelength

• Wavelength is the distance a sound wave travels during one cycle
• Higher frequency is a short wavelength and low frequencies have ling wavelengths

Wavelength formula

• λ = c/f
• λ = wavelength
• c = speed of sound
• f = frequency

Tube Resonance equation

• f = c​​/λ = c / 4L
• f is frequency
• L is tube length
• c is speed of sound (34,300 cm/s)

Vocal Tract Formulations

• F1 = c/4L
• F2 = 3c/4L
• F3 = 5c/4L

Antinode

• A reflected wave is in phase with an incident wave, causing constructive interference

Node

• A reflected wave that is 180 degrees out of phase, causing destructive interference or an absence of sound

Inhalation

• The diaphragm contracts down and forward
• External intercostals contract
• Thoracic cavity expands
• Lung volume increases

Exhalation

• Passive exhalation involves plastic recoil and diaphragm relaxation
• Active exhalation involves speaking below the end expiratory level (EEL) (EEL)
• Internal intercostals and abdominal muscles contrac
• Lung volume decreases

Volume

• The amount of space a substance occupies

Capacity

• The maximum amount that something can contain

Vital Capacity

• The maximum amount of air a person can exhale from their lungs after taking a deep breath
• VC is generally greater in males than in females

Speech Breathing Changes

• Major changes in location of air intake
• Inhale/exhale ratio rate
• Volume of air inhaled / Cycle
• Muscle activity for exhalation

Structures of Phonation

• Hyoid bone
• Cartilages: epiglottis, thyroid, arytenoids, and cricoid

Muscles that Control Vocal Folds

• Lateral cricoarytenoid > Adduct VF or together
• Interarytenoids
• Posterior cricoarytenoid >  Abduct VF or Apart
• Thyroarytenoid > Tense VF
• Cricothyroids >  Elongate + Tense VF

Myoelastic Aerodynamic Theory

• Vocal Fold (VF) generate sound by vibrating air coming through larynx from lungs
• VF vibration controls pitch
• Lower frequency = lower pitch
• Higher frequency = higher pitch
• Medial compression: Pbelow VF > Pabove VF
• VF bottom opens from bottom to top

Bernoulli Effect

• A tight space causes air flow to increase
• Outward pressure diminishes
• Negative pressure brings Vocal Folds (VF) together

Vertical Phase Difference

• VF open + close from bottom to top

Longitudinal Phase Difference

• VF opens back to front
• VF closes front to back

Vocal Fold vibration

• Vocal Folds (VF) do not vibrate in completely even, periodic manner

Jitter

• Fluctuations in frequency. (VF Vibration)

Shimmer

• Fluctuation in amplitude pressure above/ below VF)

Standing Wave

• A wave that's continuing in system

First harmonic

• Fundamental frequency (f0) 
• The frequency that will perform that best in system: loudness and efficiency.
• Formants = odd # harmonics, 1
• F2 = 2nd formant
• F3 = 3rd formant + 3rd harmonic

Sound Nature

• Sound is comprised of 21% Oxygen, 1% Argon, 78% nitrogen