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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. Physics of Sound. Loudness is determined by the amount of pressure produced by a wave measured in decibels

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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


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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


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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


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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


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Sound Equipment

  • Camcorder mics work well for short distances, the inverted square rule

  • Professional camcorders give you audio level control, consumer ones often don’t

  • Using mics outside the camcorder offers more flexibility in shot choice and the chance to have a master soundtrack


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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


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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


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Sound Equipment

  • Microphone directionality

    - polar diagrams show sensitivity from above

    - hyper/super cardiod (shotgun) mics do not magnify sound, but exclude it


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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


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Sound Equipment

  • Stereo Mics

    - X-Y configurations are usually built into camcorders

  • uses two cardioid mics each pointed 45˚ to the side


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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


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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


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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


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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 don’t overmodulate easily


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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


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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


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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


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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


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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


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Recording Techniques

  • Position mics to avoid reflected sound from the camera


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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


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Recording Technique !

  • Capturing sound effects

    - sounds directly captured from the environment

    - sounds from a sound library or from the internet

    - foley sounds


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Sound’s 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


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Sound’s 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


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Sound’s 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


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