Physics of Sound

1
Physics of Sound

• Sound is a series of atmospheric pressure waves
  produced by a vibration
• The height (amplitude) corresponds to loudness
  and the wavelength to frequency

2
Physics of Sound

• Loudness is determined by the amount of pressure
  produced by a wave measured in decibels
• An increase of 10 decibels equals twice the
  volume
• Threshold of hearing is the softest audible
  sound, threshold of pain is 130dB. A normal
  conversation is 65 dB above the threshold of
  hearing
• Dynamic range highest to lowest point

3
Physics of Sound

• Frequency determines the pitch of a sound
• The cycles of waves are measured in hertz (Hz) or
  cycles per second. Western instruments use 440
  Hz as a standard for the pitch A
• Doubling the frequency octave
• Ear is more sensitive to midrange frequencies
  than to low or high frequencies

4
Physics of Sound

• Frequency response refers to how an audio system
  or microphone responds to various frequencies
• Good audio recorders are capable of flat or equal
  response to all frequencies, consumer camera mics
  may not be
• Using equalizers to change the frequency response
  for given ranges of any sound changes the nature
  of that sound

5
Sound Equipment

• Camcorder mics work well for short distances, the
  inverted square rule
• Professional camcorders give you audio level
  control, consumer ones often dont
• Using mics outside the camcorder offers more
  flexibility in shot choice and the chance to have
  a master soundtrack

6
Sound Equipment

• Microphone types
• - dynamic or moving coil are quite rugged,
  resistant to hand noise, require no battery
• - condenser mics are more sensitive and require
  a power source
• - electret condenser mics have a permanently
  charged capacitor and may be small and require no
  power supply

7
Sound Equipment

• Microphone directionality
• - omni-directional mics respond equally to
  sounds from any direction
• - cardioid mics are most sensitive to sounds
  comimg from the front, less to the sides, and
  least to the back
• - super-cardioid mics are insensitive to sounds
  not coming from the front

8
Sound Equipment

• Microphone directionality
• - polar diagrams show sensitivity from above
• - hyper/super cardiod (shotgun) mics do not
  magnify sound, but exclude it

9
Sound Equipment

• Lavalier mics or lapel mics
• - useful for recording individuals in noisy
  environments
• - the resonation of sound in the chest can make
  the voice sound low and unnatural

10
Sound Equipment

• Stereo Mics
• - X-Y configurations are usually built into
  camcorders
• uses two cardioid mics each pointed 45 to the
  side

11
Sound Equipment

• Stereo mics
• - M-S (mid-side) mics uses a cardioid mic facing
  forward and a figure 8 mike for the sides
• - useful for mixing down if you have good
  editing equipment

12
Recording Techniques !

• Controlling microphone noise
• - wind across the microphone creates loud
  rumbles, crackle, and pops
• - wind screens and blocking objects help
• - handling of the microphone or touching of the
  camera and vibrations from the tripod can also
  create noise

13
Recording Techniques

• Microphone distance
• - ideally 1-3 feet, camcorder mics record speech
  accurately up to about 5 or six feet
• - too close, breathing, s sounds, pops, bass
  tone proximity effect
• - to far away means more ambience sound
• - compromised sound perspective can be adjusted
  with reverb

14
Recording Technique !

• Digital recording levels and overmodulation
• - overmodulated (too loud) analog sounds becomes
  crackly, with digital recording, it is distorted
  and clipped off
• - digital recordings should be concerned more
  with recording too loud, though camcorders dont
  overmodulate easily

15
Recording Technique

• Camcorders and Automatic Level Control
• - ALC or automatic gain control works by
  adjusting the recording level based on the signal
  it receives
• - test the sound signal in your environment to
  see of any radical level changes take place

16
Recording Technique

• Ambient sound
• - the background sound in any production can be
  minimized by turning off appliances, choosing
  quiet times and spaces, or using sound blankets
• - record about a minute of room tone at every
  location
• - ambient sound should be consistent from one
  shot to the next

17
Recording Technique !

• Noisy locations
• - get the mic as close to the source as possible
  
• - use lavalier mics
• - use directional mics like shotgun mics and
  position your subject outside of a major noise
  source
• - ideal to have two sound sources, subject and
  background

18
Recording Technique !

• Acoustic space
• - live spaces reflect sound and cause echos,
  such as empty rooms with hard smooth walls and
  floors
• - dead spaces absorb the sound, such as carpeted
  rooms with lots of furniture and irregular walls.
  
• - outdoor spaces can be dead because they have
  no reflecting surfaces

19
Recording Technique

• Controlling reflected sound
• - a live room can produce a muddled
  reverberating sound
• - you can minimize reverberation
• - close directional
• - deaden walls and floor with
  curtains/blankets
• - you may use reflected sound to your advantage

20
Recording Techniques

• Position mics to avoid reflected sound from the
  camera

21
Recording Technique

• Narration
• - voice over tracks are ideally recorded in
  sound proof environments. A make shift one can
  be made out of sound blankets
• - off screen narration gives the video a sense
  of omniscience, objectivity, and predestination

22
Recording Technique !

• Capturing sound effects
• - sounds directly captured from the environment
• - sounds from a sound library or from the
  internet
• - foley sounds

23
Sounds Impact on Image

• High pitch tension, suspense
• Low pitch less tension, mystery
• Loud sounds intense, threatening
• Quiet sounds delicate, hesitant
• Fast tempo more tension
• Silence highlights, isolates image, can
  represent death, sticks out if a mistake

24
Sounds Impact on Image !

• Sound effects both atmospheric and diagetic
• Off screen sounds can expand the film world
  beyond the frame
• Sounds can be used like motiffs and serve
  symbolic functions
• Sounds can be used as to aid transitions and
  foreshadow action

25
Sounds Impact on Image !

• Music
• - sets a mood
• - suggest historical references, a time period
• - can suggest locales, classes or ethnic groups
• - used as foreshadowing and musical warnings
• - atonal music can create anxiety
• - can reference other settings of music
• - music can provide ironic contrasts with image