Acoustics II Test Flashcards
Oscillation
repetitive or periodic variation, typically in time, of a wave about a central value or between two or more different states
Cycle
the time between a point on a wave and the same point on the next iteration of the wave
Frequency
the number of wave cycles that pass by each second, and is measured in Hertz (Hz)
Frequency range of human hearing
20Hz to 20,000 Hz
Infrasonic Sound
sounds below human hearing range
Ultrasonic Sound
sounds beyond human hearing range
Sine Wave
- a periodic wave whose waveform (shape) is the trigonometric sine function
- a single frequency with no harmonics
- considered an acoustically pure tone
Resonance
Frequency/Speed at which something naturally vibrates
Sympathetic Vibration
vibration of sound & resonance from a source that causes other objects/instruments to resonate in the same room without being physically played
- pianos, drums, sitars, etc
Just Intonation
tuning intervals as whole number ratios of frequencies
Equal Temperament Tuning
approximates just intervals by dividing an octave into steps such that the ratio of the frequencies of any adjacent pair of notes is the same
- stretched tuning
A 440
A4 (above middle C)
Concert Pitch for orchestras
Scales
major, minor, modal
western v. eastern music
(microtonal)
Intervals
the distance between two notes
Spectrum of pitch perception
Amusia - tone deaf
Relative Pitch
Absolute/Perfect Pitch
Consonance
together/with
Dissonance
clashy/unpleasant/unresolved
Unison
Same Pitch
Beats
near unison but slight phasing issues, sound cuts in and out
Harmonic Series
Fundamental: starting pitch
Partials: all frequencies that make up a sound
Overtone: partials that are whole number multiples of the fundamental (harmonics) (pitched or unpitched)
Timbre
tone quality
balance between frequencies
Frequency Masking
sounds that cover up other sounds, esp in the same freq range
Noise
random sounds
Harmonic sound
pitched sound
Frequency response
measure of how something affects the timbre of the sound
Fletcher-Munson Curves
a set of experimentally determined graphs that show how loud—in dB SPL—a sound at one frequency must be to be perceived as equally loud as a sound at another frequency
Bandwidth (Q)
the width of frequencies being manipulated in an EQ
- Q control can narrow or widen this curve
Wavelength
the length of the wave measured in feet
Bass - long wavelength
Treble - short wavelength
Wavelength equation
Wavelength = (speed of sound)/frequency
Speed of sound
1125 feet per second
Audio Filters
LPF: Low Pass Filter
HPF: High Pass Filter
Band Reject: cuts out a band
Notch: narrow band reject
Resonant: emphasize/ suppress the harmonics of a frequency
Shelving (EQ)
move up/down desired freq and all above/below point
Peak/Bell (EQ)
cutting/boosting a chosen freq and those surrounding it, determined by Q
Boost or cut (EQ)
amplify or attenuate a frequency
Sweep or switchable (EQ)
Sweep - fine tuning and smooth EQ controls
Switchable - set points on EQ predetermined by manufacturer
Active or passive (EQ)
Active: needs power to operate, good isolation, signal boost w/amps
Passive: no noise, reduces signal, high dynamic range
Exciters & psychoacoustic processors
- add harmonic distortion
- change phase
- add/subtract bass
Pitch Processors
harmonizers/pitch shifters, Auto-Tune, Melodyne
Subharmonic Synth/Bass Synth
generates lower octaves
Wavelength
physical length of a wave
measures in feet/inches/meters
Frequency
waves per unit of time (second)
Cycles per second = Hertz (Hz/kHz)
Period (1/f)
how much time for a cycle
measured in seconds/milliseconds per cycle
Speed of sound
Velocity of wave through a medium
767 miles per hour
1125 feet per second
