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