MUS 244: Acoustics & Synthesis Vocabulary

A comprehensive vocabulary flashcard set covering foundational concepts in acoustics, sound wave physics, music theory intervals, harmonic series, filtering, and synthesis methods from MUS 244.

Sound

A pressure wave and transfer of kinetic energy created by vibrations moving through a medium (such as air, liquid, or solid), which the inner ear's cochlea converts into electrical energy.

Longitudinal Wave

A wave in which particle displacement is parallel to the direction of wave propagation, representing how sound waves physically travel through a medium.

Transverse Wave

A wave in which particle displacement is perpendicular to the direction of wave propagation, commonly used as a graphical representation of sound waves.

Compression

A region in a longitudinal sound wave where medium particles are compressed close together, resulting in increased pressure.

Rarefaction

A region in a longitudinal sound wave where medium particles are spread apart, resulting in decreased pressure.

Crest

The peak or highest point of maximum positive displacement on a wave.

Trough

The valley or lowest point of maximum negative displacement on a wave.

Wavelength

The physical distance required to complete one full wave cycle.

Amplitude

The height of a wave indicating how compressed the molecules are, perceived subjectively as volume or loudness and measured in decibels ($dB$).

dB FS (Decibels Full Scale)

A digital amplitude measurement scale used in computers where $0\,dB\,FS$ is the maximum loudness a system can handle before clipping.

dB SPL (Sound Pressure Level)

An acoustic amplitude measurement scale used in physical space where $0\,dB\,SPL$ represents the threshold of human hearing.

Periodic Wave

A sound wave characterized by regular, predictable repetition over time that produces a perceivable pitch.

Aperiodic Wave

A sound wave lacking regular repetition or pattern, having no distinct pitch and perceived as noise.

Frequency

The number of completed wave cycles per second in a periodic wave, measured in Hertz ($Hz$) or kilohertz ($kHz$), which human hearing perceives as pitch.

Hertz ($Hz$)

The standard unit of frequency measurement, equivalent to one cycle per second ($1\,Hz = 1/\text{sec}$).

Threshold of Human Hearing

The range of frequencies audible to humans, spanning from $20\,Hz$ to $20\,kHz$ ($20,000\,Hz$).

Infrasound

Sound waves with frequencies below the lower limit of human hearing ($< 20\,Hz$).

Ultrasound

Sound waves with frequencies above the upper limit of human hearing ($> 20\,kHz$).

Octave

The musical interval created by doubling ($2 \times$) or halving ($1/2$) a sound's frequency.

Oscillator

An electronic component or signal source that moves electricity back and forth to generate a sound wave.

Timbre

The unique quality, tone color, or acoustic character of a sound that distinguishes different instruments or voices playing the same pitch and loudness.

Pulse Wave

A nonsinusoidal waveform (also called a rectangle wave) whose timbre changes depending on its pulse width ratio.

Constructive Interference

The wave phenomenon occurring when two waves of the same frequency and in phase combine, adding their amplitudes together to create a wave with twice the amplitude.

Destructive Interference

The wave phenomenon occurring when two waves of the same frequency that are $180^\circ$ out of phase combine, causing their opposite amplitudes to cancel each other out.

Polarity Inversion

The process of flipping a wave upside down by multiplying its amplitude values by $-1$, equivalent to a $180^\circ$ phase shift on a periodic wave.

Active Noise Cancellation

Headphone technology that uses a built-in microphone to capture ambient noise, invert its polarity, and play back the inverted signal to cancel noise via destructive interference.

Beats

The rhythmic pulsing effect created by alternating constructive and destructive interference when two pure tones of slightly different frequencies ($< 20\,Hz$ apart) play simultaneously.

Phasing

A compositional technique or process where two identical repeating patterns or signals run simultaneously with one playing at a slightly faster frequency or tempo than the other.

Fundamental Frequency

The lowest frequency ($1\text{st}$ partial) of a sound wave, which determines the overall perceived pitch of a periodic sound.

Harmonic Series

A set of frequencies consisting of positive integer multiples of a fundamental frequency ($x, 2x, 3x, 4x, \dots$).

Fourier Transform (FFT)

A mathematical algorithm (Fast Fourier Transform) that decomposes any complex periodic signal into the individual pure sine waves that make it up.

Spectrogram

A three-dimensional spectrum analyzer display showing frequency on the vertical axis, time on the horizontal axis, and amplitude represented by colors or brightness.

Additive Synthesis

A method of sound synthesis that builds complex tones by combining multiple individual sine waves at different frequencies and amplitudes.

Subtractive Synthesis

A method of sound synthesis that starts with a harmonically rich waveform (such as a sawtooth or pulse wave) and uses filters to remove unwanted frequencies.

Low-Pass Filter

An audio filter (also known as a high cut) that lets low frequencies pass through while attenuating high frequencies above its cutoff frequency.

High-Pass Filter

An audio filter (also known as a low cut) that lets high frequencies pass through while attenuating low frequencies below its cutoff frequency.

Bandpass Filter

An audio filter that allows a specific frequency band to pass through while attenuating frequencies both above and below that region.

Parametric EQ

A flexible equalizer (also called a bell EQ) that allows boosting or cutting specific frequency regions using controls for center frequency, gain, and $Q$ (bandwidth).

Shelf Filter

An equalizer filter that boosts or cuts all frequencies above (high shelf) or below (low shelf) a cutoff frequency and flattens out to maintain that level shift.

LFO (Low Frequency Oscillator)

An oscillator operating below the threshold of human hearing ($< 20\,Hz$) used to modulate synthesizer parameters like pitch, cutoff frequency, or amplitude repetitively over time.

ADSR Envelope

A four-stage modulation generator—comprising Attack, Decay, Sustain, and Release—that shapes a sound parameter over time when a note is pressed and released.

Modular Synthesis

A synthesizer system constructed from physically separate functional hardware modules whose signal routing is created manually using patch cables.

Wendy Carlos

An American electronic musician, composer, and pioneer of Moog modular synthesis who released the groundbreaking $1968$ album Switched-On Bach.

Isao Tomita

A Japanese electronic music pioneer known for using large Moog modular systems and multitrack recording to create orchestral synthesis albums such as Snowflakes Are Dancing ($1974$) and The Planets ($1976$).