EDAU 115 Exam 2 Study Guide

Based on Assignment 1, the study guide, and items on the slides.

sound

sound

the transfer of energy through an elastic medium

What are the three necessary components for sound to occur?

1. energy - ex: lungs

2. a body capable of vibration - ex: vocal folds

3. transmitting medium - ex: air

What are the physical properties of a sound source and transmitting medium?

1. the source must be able to vibrate; vibration requires mass and elasticity

2. the medium must be capable of being set into vibration; it also requires mass and elasticity

mass

the amount of of matter present

weight

gravitational force on an object

mass vs weight

our mass is the same on Earth and on the moon, but our weight would be different ex: A 110 lb person on Earth would be 18 lbs on the moon, but the mass would be the same regardless where they are

density

the amount of mass per unit volume

elasticity

the property that enables recovery from distortion of shape or volume ex: air

pressure

the amount of force per unit area ex: atmospheric pressure is 14.7 lb / in²

Why aren’t we able to hear sound in space?

There are too few particles, meaning there is nowhere for sound to go or any air molecules to bump into

simple harmonic motion

the swaying back and forth motion of molecules or a disturbance in a medium in which particles are disturbed perpendicular to the direction of disturbance; also known as sinusoidal motion

condensation

when simple harmonic motion occurs, particles in a medium are pushed together

rarefaction

when simple harmonic motion occurs, particles in a medium are pulled apart

What are the 5 measurements of a sine wave?

1. amplitude

2. frequency

3. period

4. phase

5. wavelength

amplitude

perceptually equates to loudness; maximal displacement of particles in a medium

rms amplitude

average amplitude of the waveform over time (rms = 0.707 x peak amplitude); used to measure the amplitude/intensity of a voice

frequency

number of complete cycles per second (Hz); pitch = the perceptual correlation of frequency; pitch associated with human voice = F0 ex: 250 Hz higher perceived pitch than 100 Hz

f= 1/T

cycle

a complete repetition of the oscillation

simple sounds

single frequency (pure tone ex: tuning fork); not commonly found in nature and has no change in frequency; useful for tests and measurements

complex sounds

sounds containing more than 1 frequency (speech)

period

time that it takes for a vibrating object to complete one cycle of vibration

T = 1/f

phase

represents the point in the cycle at which the vibrating object is located at a given instant in time

in-phase

two sinusoids are in phase when their wave disturbances crest and trough at the same time

out-of-phase

sine waves (180°) are out of phase when they are out of sync, and thus create a cancellation effect; commonly used for active noise reduction systems ex: headphones

wavelength

distance that a sound wave travels during one complete cycle of vibration

λ=s/f - measured in meters (f in Hz and speed = 340 m/sec)

frequency vs wavelength

they have an inverse relationship; low frequency = longer wavelength, high frequency = shorter wavelength

decibel

unit used for measuring the amplitude/intensity (loudness) of sound; we use decibels because it makes our numbers easier to work with and interpret

peak clipping

Peaks of the waveform are cut off due to amplifier circuits being overdriven

Solutions: dynamic compression and limiting —> makes sounds more consistent

transverse wave

the medium is displaced perpendicular to the direction of the traveling wave ex: light

longitudinal wave

the medium is displaced parallel with the direction of the traveling wave ex: sound

speed of sound

depends on 2 properties: 1. stiffness 2. density

high speed of sound depends more on the stiffness of dense materials

imperial system

foot, pound, second (fps)

metric system

meter, kilogram, second (mks); centimeter, gram, second (cgs)

band pass filter

signals that only allow certain frequencies through the system; reason why voice sounds thin + raspy over the phone

300-3,400 Hz band pass filter - sounds most important for speech

Note: digital systems like Face Time are not tied down by band pass, which is why FT is crisper since not much filtering is occurring

fundamental frequency

the lowest rate of vocal fold vibration (F0, first harmonic); associated with pitch - smaller/shorter vocal folds will vibrate at a higher frequency than larger/longer vocal folds (the reason why children have higher-pitched voices)

F0 of adults = 80-300 Hz

F0 of children = 200-500 Hz

harmonics

an integer multiple of the fundamental frequency

ex: F0 = 100 Hz, 2nd harmonic =200 Hz, 3rd= 300 HZ, 4th= 400Hz

F0 = 150 Hz, 2nd= 300 Hz, 3rd = 450 Hz

Which harmonics make up formants necessary for vowel discrimination?

3rd and 5th harmonics

formants

created by the resonance of sound transmitted through the vocal tract

What is the relationship between vocal tract length and formant frequencies?

formants have an inverse relationship with vocal tract length

ex: longer vocal tract = lower frequency formant values; shorter vocal tract length = higher frequency formant values

Which tongue positions affect F1 and F2?

F1 is determined by the tongue height (the higher the tongue is, the lower the frequency); F2 is determined by the back-ness/forwardness (the further forward the tongue, the higher the frequency)

F3

related to vocal tract length

acoustic resonance

an object or a system vibrates at a specific natural frequency when exposed to an external sound wave or vibration; all objects have a frequency at which they vibrate best at

cavities/spaces

generally have lower resonant frequencies, smaller cavities have higher resonant frequencies (based on particle velocity and wavelength)

categorical perception

the psychoacoustic phenomenon where sounds are generally perceived as distinct categories; perception changes rapidly when some acoustic attribute (ex: VOT) is varied

source filter theory

describes acoustic output during speech-sound production; comprised of:

1. source - voiced or voiceless signal

2. filter ex: vocal tract

voice onset time

refers to the duration between the release of a plosive/stop sound and the beginning of vocal fold vibration; voiceless consonants have longer VOT than voiced consonants

long term average spectrum (LTAS)

describes the frequency (pitch) distribution of energy for speech produced over a brief period of time (1-2 minutes); decreases in amplitude at about -6 dB/octave

male vs female LTAS

• LTAS for male speakers contains more energy below 1000 Hz

• female voices have increased high-frequency energy

What are the 3 factors used to classify consonants?

1. place - location of airflow restriction in the oral cavity during speech production

2. manner - how sound is produced

3. voicing - presence or absence of vocal fold vibration

Ling 6 speech sounds test

sound test that is a set of 6 speech sounds: /ɑ, i, u, ʃ, s, m/

each sound represents a frequency region (low, mid, high)

commonly used as a daily biologic check to confirm amplification device function (hearing aids)

continuous signal

a signal that has a value at any given time

discrete signal

a signal produced by sampling amplitude at a given rate

amplitude quantization

capturing the amplitude of the continuous signal, more bits = more lvls of amplitude

What does a high bit rate wave look vs. a low bit rate wave?

most current digital systems use 16- or 24-bit, as these values provide for sufficient and high-quality reproduction of continuous signals for most auditory applications

sampling frequency/rate

refers to the number of amplitude samples taken (i.e. sampled points) in a given period of time, typically one second

commercially available audio and speech processing systems, ranging from 8kHz to over 300 kHz

ex: sampling freq. of 16 kHz means that amplitude values are obtained 16,000 times each second

Nyquist Theorem

states that the sampling frequency required for a given application must be at least twice that of the highest frequency of interest in the output signal (at least two samples per cycle are required)

ex: for 20 kHz, sample rate would be 40 kHz

According to the Nyquist Theorem, what is the minimum sampling rate required to accurately digitize a 20,000 Hz sine wave?

40 kHz (20,000 Hz = 20 kHz), so 20kHz x2

aliasing

occurs when a signal is sampled at a frequency that is insufficient for the application; distortion that occurs when reconstructed digital signal is different from the original signal - occurs when Nyquist Theorem has been violated

auditory recruitment

when quiet sounds become inaudible and loud sounds become uncomfortable; result of sensory hearing loss (cochlear outer hair cell damage) leads a reduced dynamic range and abnormal growth of loudness

solution: hearing aids, can help amplify sounds and compressor helps with maintaining lvls of sound

How does stiffness and density of a medium affect the speed of sound?

greater stiffness of a medium will result in greater speed —> determines speed better than density, but less density of the medium will result in greater speed

ex: sound is faster in water than in air due to the greater stiffness of water

Label the axis of the spectrogram of the vowel sound /i/ using the following values: F1, F2, F3

F1 250 Hz, F2 2,200 Hz, F3 2,800 Hz