Acoustics Midterm

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  1. acoustic isolation:
    minimize bleed between rooms
  2. acoustic separation:
    minimize bleed between mulitple mics within the same room
  3. transmission loss:
    how much sound is lost when it passes through something
  4. what will make a wall have more transmission loss?
    if it's thicker (it vibrates less)
  5. rigid fiberglass:
    it doesn't vibrate well, so it's good for absorbing sound in walls
  6. staggered studs:
    stagger the studs in the walls so they hold the wall in place but they don't vibrate on each other
  7. Types of acoustic treatment:
    • absorber (decrease reverb time)
    • diffusers
  8. Longitudinal waveform:
    air molecules compressing and expanding (like when you pluck a guitar string)
  9. Transverse waveform:
    the waveform you see drawn in pro tools
  10. Amplitude:
    height of the wave, relates to loudness
  11. RMS amplitude:
    mean of amplitude, about 70% of peak-to-peak amplitude
  12. λ wavelength:
    determines pitch of note
  13. Frequency formula:
    1130ft./sec. ÷ λ (wavelength)
  14. Frequency:
    # of cycles per second
  15. Timbre:
    sonic characteristic of the sound
  16. envelope:
    how amplitude changes over time (ADSR)
  17. Harmonics:
    layers of tones on the fundamental note
  18. Propagation:
    how sound travels from point A to B
  19. How does sound travel? (direction)
  20. When the day is drier, how does this affect sound?  Humid?
    Dry means it slows down, humid means it speeds up (more molecules to move)
  21. How to calculate distance:
    • Rate * Time = Distance (also for time delay)
    • Rate is always 1130ft./sec.
  22. Reflection:
    sound bouncing off something
  23. Absorption:
    sound NOT bouncing off something, friction causes sound to turn into heat
  24. Diffusion:
    scattering of sound
  25. diffraction:
    sound bending through an opening or around an object (causes acoustic shadow)
  26. Transmission:
    sound going through something (low freq. transmit better)
  27. Radiation Pattern:
    how sound propagates in 360°
  28. Phase:
    a point in time of a sound's wavelength
  29. interference:
    • Constructive: waves combine when they are in phase and add loudness
    • Destructive: wave out of phase and cancel each other out
  30. Flange:
    time delay of doubled sound (also comb filter)
  31. Chorus:
    pitch shift of doubled sound
  32. Beats:
    difference between 2 close frequencies and they begin to beat at that frequency
  33. binaural beat:
    2 different signals coming from either side that are beating
  34. What does a spaced pair rely on for stereo image?
    phase differences
  35. what does x/y pair rely on for stereo image?
    time delay (no phase, but not very wide)
  36. Sound pressure level:
    amount of air molecule displacement
  37. Dyne/cm2
    amount of molecules moving in 1 cm2
  38. formula to compare two distances
  39. what is a decibel?
    a ration between 2 levels (at source and perceived)
  40. what is the lowest volume we can hear at?
    .0002 dyne/cm2
  41. dB SPL
    dB V
    dB m
    • air traveling through air
    • volts
    • watts (power; what is used mostly in the studio)
  42. what happens when you add or cut 3dB?
    boost/cut level by double/half, only sounds a little louder/softer to us
  43. when you add/cut 1dB?
    hardly noticeable
  44. Formula for adding/subtracting 2 decibel levels:
    10log(10x/10 ± 10y/10)
  45. Outer ear:
    • pinna (helps us tell up and down)
    • ear canal (takes sound to eardrum)
  46. Middle ear:
    • eardrum
    • ossicles (hammer, anvil, stirrup; connect eardrum to cochlea and help protect inner ear from damage when fatigued)
  47. Inner ear:
    • cochlea (filled w/ fluid, stereocilia transmit fluid vibration to auditory nerve)
    • auditory nerve (carry signal to brain)
  48. Doppler effect:
    when pitch changes as distance changes
  49. Combination tones:
    if 2 frequencies are greater than 50Hz apart, you will hear sum and difference of the 2 freq.
  50. What do the Fletcher-Munson curves tell us?
    hearing gets flatter as it gets louder, need to turn up bass when it's quiet
  51. measurement of perception of loudness is measured in:
  52. Ways to avoid masking:
    • EQ
    • levels
    • Panning
    • Arrangement
    • Depth (reverb/delay)
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Acoustics Midterm
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