# Acoustics

Mind Map by Luke Byrne, updated more than 1 year ago
 Created by Luke Byrne over 2 years ago
29
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### Description

Linguistics Mind Map on Acoustics, created by Luke Byrne on 04/30/2018.

## Resource summary

Acoustics
1 Speech Chain
1.1 Ling > Phys > Acoustic > Phys > Ling
2 Propagation of sound
2.1 Sine wave
2.1.1 Particle move & pressure variation in space
2.1.2 Pure tone
2.1.2.1 Basis of complex, periodic sounds
3 Sound waves
3.1 Frequency
3.1.1 Hz (number of cycles per second)
3.1.1.1 Healthy ear: 20-20,000Hz
3.1.1.2 Cycle (complete vibration)
3.1.1.2.1 Period = T = duration of complete cycle (s)
3.1.1.2.1.1 T = 1/f (s)
3.1.2 Speed of sound
3.1.2.1 c = 331.4*sqrt(1+Temp/273)
3.1.2.1.1 c = 340 m/s as approx value
3.1.2.2 Freq. does not determine speed a wave travels at
3.1.3 Wavelength (spatial period of wave)
3.1.3.1 λ = c / f [m]
3.1.4 Pitch
3.1.4.1 Freq. closely related to (but not the same as) pitch
3.1.4.1.1 Freq = physical props. of sound
3.1.4.1.2 Pitch = sensation
3.1.4.1.3 near-linear up to 1 kHz - listener's sensitivity decreases as we go higher in freq.
3.1.5 is independent of
3.1.5.1 Tuning fork emits the same freq. regardless of how hard it has been struck
3.2 Amplitude
3.2.1 dB (size of variation in air pressure)
3.2.1.1 peak deviation from normal atmospheric pressure
3.2.1.2 how forceful the wave is
3.2.1.2.1 Decibels = relative loudness of sounds in air
3.3 Phase
3.3.1 degrees (starting point of a wave along the y-axis)
3.3.2 Situation of the cycle of oscillation at a particular moment
3.3.3.1 In-phase = largest output
3.3.3.2 In intermediate phase = intermediate output
3.3.3.3 In opposite phase = zero output (silence)
4 Sound Classification
4.1 Periodic
4.1.1 Complex
4.1.1.1 >1 frequency
4.1.1.2 freq's which are int. multiples of lowest one = fundamental = f0 = H1
4.1.1.3 Power Spectrum (Amp Spectrum or Magnitude Spectrum)
4.1.2 Fourier's theorem
4.1.2.1 A periodic function, f(x), which is reasonably continuous may be expressed as the sum of a series of sine or cosine terms (called the Fourier series), each of which has specific AMPLITUDE and PHASE coefficients (known as Fourier coefficients)
4.1.2.1.1 Fourier Transform
4.1.2.1.1.1 Discrete Fourier Transform (DFT)
4.1.2.1.1.1.1 Time-domain to Freq-domain
4.1.2.1.1.1.1.1 Freq-domain repres. = Hz (freq - X) vs. dB (amp - Y)
4.1.2.1.1.2 Fast Fourier Transform (FFT) - fast algo for DFT
4.1.2.1.1.3 Breaks into sine and cosine waveforms
4.2 Aperiodic
4.2.1 Continuous (fan, engine)
4.2.2 Transient (door closing)
5 Sound
5.1 Energy produced by a vibrating source which travels through the air
5.1.1 Vibration: simple harmonic motion (SHM)
5.1.1.1 Elasticity (bounce back)
5.1.1.2 Inertia (keep moving)
5.1.1.3 Periodic
5.1.1.4 Amp decreases
5.2 Movement of air particles -> variation in air pressure
5.2.1 Compression (high pressure)
5.2.2 Rarefaction (low pressure)
5.2.3 Longitudinal wave (pushes and pulls)

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