Unit 1 Study Guide — Sound, Acoustics, and Signals

Vocabulary practice flashcards covering fundamental acoustic concepts, wave properties, speech and music signals, digital processing, decibel scales, immittance, and measurement scales.

Sound

A mechanical wave produced by vibration that requires a medium such as air, water, or a solid to travel, and cannot travel through a vacuum.

Free Field

A sound field in which sound travels without significant reflections or obstacles, such as in an anechoic chamber or sound booth.

Diffuse Field

A sound field in which sound reaches a location from many directions because of reflections, sometimes described as an interaction room.

Mass / Inertia

The property of a medium where particles resist changes in motion.

Elasticity / Stiffness

The property of a medium where particles return toward their original resting position after displacement.

Simple Harmonic Motion

Repetitive back-and-forth movement around an equilibrium or resting position, classically represented by a sine wave.

Frequency

The number of cycles per second, measured in Hertz ($\text{Hz}$), which is related to perceived pitch.

Amplitude

The magnitude or strength of a wave, associated with particle displacement, pressure, and loudness.

Phase

The position within a cycle that describes where in the cycle the wave begins.

Period

The amount of time required to complete one cycle.

Wavelength Formula

The equation $\lambda = \frac{c}{f}$, where $\lambda$ is wavelength, $c$ is the speed of sound ($\approx 340\,\text{m/s}$), and $f$ is frequency.

Brownian Motion

Random, rapid movement of particles in a medium.

Condensation

An area of high particle density created as a sound wave travels through a medium.

Rarefaction

An area of low particle density created as a sound wave travels through a medium.

Periodic Sound

A waveform that repeats itself over time and contains a fundamental frequency and harmonically related frequencies.

Aperiodic Sound

A waveform that does not repeat regularly over time, with noise being a common example.

Fundamental Frequency ($f_0$)

The lowest frequency component of a periodic complex wave, representing the wave's home base.

Harmonics

Frequency components occurring at integer multiples of the fundamental frequency.

Overtones

Frequency components occurring above the fundamental frequency.

Octave

An acoustic interval representing a doubling of frequency, such as moving from $500\,\text{Hz}$ to $1000\,\text{Hz}$.

Temporal Envelope

The smooth contour tracing changes in amplitude over time, which speech understanding heavily relies upon.

Acoustic Fine Structure

Detailed frequency information involving fundamental frequency, harmonics, overtones, and octaves, which music depends on more heavily than speech.

Time Domain

A representation of sound showing how amplitude or pressure changes over time.

Frequency Domain

A representation of sound that separates a complex sound into its individual frequency components and their amplitudes.

Spectrogram

A visual representation combining frequency and time, where darker areas represent greater acoustic intensity.

Formants

Resonance peaks that contain important information for distinguishing speech sounds.

Constructive Interference

Interference occurring when waves are in phase, causing their amplitudes to combine and increase.

Destructive Interference

Interference occurring when waves are out of phase, causing their amplitudes to reduce one another or cancel completely.

Diffraction

The bending or spreading of a sound wave around an obstacle or through an opening.

Head Shadow Effect

The physical blocking of sound by the head, which substantially blocks high frequencies with short wavelengths while allowing low frequencies with long wavelengths to diffract around it.

Analog Signal

A continuous signal capable of taking on an essentially infinite number of values over time.

Digital Signal

A discrete signal represented by numerical values using binary code ($0$s and $1$s).

Quantization

The process of mapping continuous analog amplitudes onto discrete numerical or binary values.

Nyquist Rule

A sampling rule stating that the sampling rate must be $\ge 2 \times \text{highest frequency}$ to avoid distortion.

Decibel ($\text{dB}$)

A logarithmic unit where an intensity doubling equals $+3\,\text{dB}$ and an intensity halving equals $-3\,\text{dB}$

$\text{dB SPL}$ (Sound Pressure Level)

A decibel scale referencing physical sound pressure, used when measuring physical acoustic output such as in hearing aid applications.

$\text{dB HL}$ (Hearing Level)

A decibel scale used clinically on an audiogram that normalizes typical human hearing thresholds to a reference threshold around $0\,\text{dB HL}$.

Acoustic Immittance

The broad framework dealing with energy flow and opposition to energy flow.

Admittance

The ease of energy or sound flow through a system.

Impedance

The opposition to energy or sound flow through a system.

Resistance

The frequency-independent component of impedance where energy is dissipated as heat.

Reactance

The frequency-dependent component of impedance where energy is stored and released.

Evidence-Based Practice (EBP)

Clinical decision-making that integrates best available research evidence, clinical expertise, and patient/client values, preferences, and circumstances.

Measurement Scales

The four scales of measurement comprising Nominal (unordered categories), Ordinal (ranked categories), Interval (equal intervals, no true zero), and Ratio (equal intervals with a true zero).

Peak Clipping

A distortion process occurring when signal peaks exceed what a digital system can accurately represent, resulting in flattened wave peaks.

High-Yield Acoustic Relationships

Key principles including inverse frequency/wavelength relationship, inverse mass/frequency relationship, direct stiffness/frequency relationship, and frequency-dependent diffraction/head-shadow interactions.