Week 1 - Acoustics Flashcards
Sound waves
compressions and rarefactions of air molecules
Compressions
Regions of increased density
Rarefactions
Regions of decreased density; restorative force and momentum
Waveform
Graphical display that represents the alternating compressions and rarefactions of air molecules that make up the longitudinal sound pressure wave
Airborn sound waves
Generated by a mechanical source - rapid vibration in air pressure
Periodic waves
Regular, repeating pattern of compression and rarefaction
Sound source is vibrating at a regular rate (F0)
Aperiodic waves
Mechanical source without regular/oscillating movement
Simple waves
Pure tones, sine waves
Consists of one tone
Not naturally occuring
Complex sound waves
More than one frequency
Either aperiodic/periodic
Combination of sine waves, each with own frequency, amplitude and phase
Frequency
Number of oscillations in a second Measured in hertz Can hear 20-20 000Hz Less cycles/sec = lower Hz, lower pitch High cycles/sec = higher H, high pitch
Air pressure
Amount of change in air pressure from sound
Relates to vertical height of waveform
Measured in Pascals, Dynes/cm^2
Decibel scale
Sound pressure and intensity simplified into 140 units
0-140dB threshold of hearing
Conversation - dB
60dB
Pain threshold - dB
130-140dB
Period
Amount of time taken to complete one cycle
Can measure duration of vowels, words, pauses during connected speech
Velocity
Speed at which the sound wave travels through a medium
wavelength = velocity/frequency
phase
Starting point of one cycle of tone/frequency
Wave length
distance travelled by one cycle of the waveform
wavelength = velocity/frequency
Decibel Scale
shows how loud a sound is relative to the threshold of hearing
Can be measured according to sound pressure level (SPL)/sound intensity (SI)
Consists of 140 points
Fundamental frequency
Main, lowest oscillation frequency of mechanical source
Harmonic Spectrum
Multiples of the fundamental
Consists of the F0 and higher harmonic frequencies
Vowel features - frequency
Periodic, therefore have periodic soundwave features;
F0 and harmonic frequencies
Pitch
Psychological correlate of F0
Loudness
Psychological correlate of amplitude
Timbre/quality
Psychological correlate of sound complexity
Psychophysical scaling
quantifies psychological dimensions of the physical properties of sound
Sone
Psychological scale of loudness
Mel
Psychological scale of pitch
Spectral Analysis
Analyses of the simple sine wave components making up complex sound
Spectrum = freq, amplitude, phase
Spectral Analysis - periodic vs aperiodic
Periodic - evenly spaced peaks
Aperiodic - no peaks
Pitch Analysis Methods
Cross Correlation
Autocorrelation
Problems with analysis
provide highly inaccurate estimates of F0; due to background noise, disordered voice, inappropriate set up for pitch analysis
Psychological correlates - frequency
pitch
Psychological correlates - amplitude
loudness
Psychological correlates - complexity
quality/timbre
depends on harmonic content, dynamic characteristics
