Music 3450 Exam 1 (Part 1: Content)

Acousmatic music

Sound heard without seeing its originating source.

Soundscape

An acoustic environment as perceived by humans.

World Soundscape Project

Soundscape research project established by R. Murray Schafer at Simon Fraser University.

R. Murray Schafer

Central soundscape figure who helped establish the World Soundscape Project.

Hildegard Westerkamp

Major composer associated with soundscape composition.

Barry Truax

Major figure associated with soundscape composition and research.

Bernie Krause

Environmental recording figure associated with Wild Sanctuary.

Reel-to-reel tape

Magnetic tape that can be cut, spliced, looped, reordered, and multitracked.

Phonograph record

Sound stored in a continuous groove; less flexible to edit than magnetic tape.

Sampling

Measuring a continuous waveform at discrete moments in time.

Sample rate

Number of samples taken per second.

Nyquist theorem

Sample rate must be at least twice the highest frequency represented.

Aliasing

False lower frequency caused by sampling a high frequency too slowly.

Anti-aliasing filter

Low-pass filter that removes frequencies too high to represent safely before sampling.

Quantization

Assigning each sampled amplitude to an available digital amplitude level.

Quantization error

Difference between the original amplitude and its quantized digital value.

Bit depth

Number of bits used per sample; determines how many amplitude levels are available.

Sample rate vs. bit depth

Sample rate controls time resolution; bit depth controls amplitude resolution.

Digital-to-Analog Converter (DAC)

Converts digital sample values into analog electrical voltage levels.

Reconstruction filter

Low-pass filter that smooths DAC output into a continuous analog signal.

Frequency

Number of waveform cycles per second, measured in hertz (Hz).

Pitch

Human perception of how high or low a frequency sounds.

Frequency vs. pitch

Frequency is physical; pitch is perceptual.

Unison

Frequency ratio of 1:1.

Octave

Frequency ratio of 2:1.

Two octaves

Frequency ratio of 4:1.

Amplitude

Physical size or magnitude of a waveform/vibration.

Intensity

Physical sound energy.

Loudness

Human perception of how strong or loud a sound seems.

Amplitude/intensity vs. loudness

Amplitude and intensity are physical; loudness is perceptual.

Acoustics

Study of the physical properties and behavior of sound.

Psychoacoustics

Study of how humans perceive sound.

Fletcher-Munson / equal-loudness curves

Show how physical level must vary by frequency for equal perceived loudness.

Time domain

Representation of amplitude, pressure, or voltage changing over time.

Frequency domain

Representation showing which frequencies are present and their strengths.

Fourier Transform

Decomposes a complex sound into sine components with frequency, amplitude, and phase.

Fourier synthesis

Combines sine-wave components to construct or reconstruct a complex sound.

DFT

Discrete Fourier Transform; mathematical transform between discrete time and frequency domains.

FFT

Fast Fourier Transform; efficient algorithm for computing the DFT.

IFFT

Inverse Fast Fourier Transform; converts frequency-domain information back toward time-domain samples.

FFT frame

A chunk of samples analyzed together by an FFT.

Frequency resolution / bin spacing

Approximately sample rate divided by FFT size: Δf = fs/N.

Large FFT frame

Provides finer frequency resolution but poorer time localization.

Small FFT frame

Provides better time localization but coarser frequency resolution.

Sine wave

Waveform containing one frequency.

Triangle wave

Waveform with odd harmonics decreasing approximately as 1/N².

Sawtooth wave

Waveform with harmonics/partials decreasing approximately as 1/N.

Square/pulse wave

Broad-spectrum waveform; a square wave commonly contains odd harmonics.

Timbre

Sound quality or character that distinguishes sounds.

Spectrum

Frequencies present in a sound and their relative strengths.

Envelope

Change in amplitude over time, including attack, sustain, decay, and transients.

Attack

Beginning portion of an envelope as a sound rises from its start.

Sustain

Portion of an envelope in which the sound is maintained.

Decay

Portion of an envelope in which amplitude decreases.

Transient

Short, rapidly changing sound component, often near a sound's beginning.

Filter

Process that passes some frequencies while attenuating others.

High-pass filter

Passes high frequencies and attenuates low frequencies.

Low-pass filter

Passes low frequencies and attenuates high frequencies.

Band-pass filter

Passes a selected frequency band and attenuates frequencies outside it.

Band-reject filter

Attenuates a selected frequency band while passing frequencies outside it.

Cutoff frequency

Frequency around which a filter transitions between pass and stop regions.

Transition band

Frequency range over which a filter changes from passing to attenuating.

FIR

Finite Impulse Response; finite response without feedback.

IIR

Infinite Impulse Response; uses feedback so previous output affects later output.

Karplus-Strong model

Plucked-string synthesis using repeated random noise and averaging/low-pass filtering.

Karplus-Strong noise buffer

Short random-noise buffer representing the initial pluck.

Karplus-Strong buffer length

Controls pitch: shorter buffer = higher pitch; longer buffer = lower pitch.

Karplus-Strong averaging

Acts as low-pass filtering, causing high-frequency content to decay.

MIDI

Musical performance/control instructions rather than recorded audio.

MIDI sequencer

Edits MIDI data such as pitch, velocity, duration, tempo, patch, and timing.

MIDI quantization

Moves MIDI note timing toward a rhythmic grid.

Multitrack audio

Actual recorded waveforms stored on separate tracks.

MIDI vs. multitrack audio

MIDI stores performance instructions; multitrack audio stores recorded sound.