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 Two Sine Waves added
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