principles of sound

7/27/2019 Principles of sound

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Physics of Sound

Sound is a series of atmospheric pressure wavesproduced by a vibration

The height (amplitude) corresponds to loudness andthe wavelength to frequency


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Physics of Sound

Loudness is determined by the amount ofpressure produced by a wave measured indecibels

An increase of 10 decibels equals twice thevolume

Threshold of hearing is the softest audiblesound, threshold of pain is 130dB. A normalconversation is 65 dB above the threshold ofhearing

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. Westerninstruments use 440 Hz as a standard for thepitch A

Doubling the frequency = octave

Ear is more sensitive to midrange frequenciesthan to low or high frequencies


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Physics of Sound

Frequency response refers to how an audiosystem or microphone responds to variousfrequencies

Good audio recorders are capable of flat orequal response to all frequencies, consumercamera mics may not be

Using equalizers to change the frequencyresponse for given ranges of any soundchanges the nature of that sound


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Sound Equipment

Camcorder mics work well for shortdistances, the inverted square rule

Professional camcorders give you audio levelcontrol, consumer ones often dont

Using mics outside the camcorder offersmore flexibility in shot choice and the chanceto 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 andrequire a power source

- electret condenser mics have a permanently

charged capacitor and may be small andrequire no power supply


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Sound Equipment

Microphone directionality

- omni-directional mics respond equally to sounds fromany direction

- cardioid mics are most sensitive to sounds comimgfrom 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 lapelmics

- useful for recording

individuals in noisyenvironments

- the resonation of soundin the chest can makethe voice sound low and

unnatural


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Sound Equipment

Stereo Mics

- X-Y configurationsare usually built intocamcorders

- uses two cardioidmics each pointed45 to the side


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Sound Equipment

Stereo mics

- M-S (mid-side) micsuses a cardioid mic

facing forward and afigure 8 mike for thesides

- useful for mixing down ifyou have good editing

equipment


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Recording Techniques !

Controlling microphone noise

- wind across the microphone creates loudrumbles, crackle, and pops

- wind screens and blocking objects help

- handling of the microphone or touching of thecamera and vibrations from the tripod can

also create noise


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Recording Techniques

Microphone distance

- ideally 1-3 feet, camcorder mics recordspeech accurately up to about 5 or six feet

- too close, breathing, s sounds, pops, basstone proximity effect

- to far away means more ambience sound

- compromised sound perspective can beadjusted with reverb


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Recording Technique !

Digital recording levels and overmodulation

- overmodulated (too loud) analog soundsbecomes crackly, with digital recording, it isdistorted and clipped off

- digital recordings should be concerned morewith recording too loud, though camcordersdont 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 thesignal 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 canbe minimized by turning off appliances,choosing quiet times and spaces, or usingsound blankets

- record about a minute of room tone at everylocation

- ambient sound should be consistent from oneshot to the next


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Noisy locations

- get the mic as close to the source as possible

- use lavalier mics- use directional mics like shotgun mics andposition your subject outside of a major noisesource

- ideal to have two sound sources, subject andbackground


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Acoustic space

- live spaces reflect sound and cause echos,such as empty rooms with hard smooth wallsand floors

- dead spaces absorb the sound, such ascarpeted rooms with lots of furniture andirregular walls.

- outdoor spaces can be dead because theyhave no reflecting surfaces


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Recording Technique

Controlling reflected sound

- a live room can produce a muddledreverberating sound

- you can minimize reverberation:

- close directional

- deaden walls and floor with curtains/blankets

- you may use reflected sound to youradvantage


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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 insound proof environments. A make shift onecan be made out of sound blankets

- off screen narration gives the video a senseof omniscience, objectivity, andpredestination


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Capturing sound effects

- sounds directly captured from the

environment- sounds from a sound library or from the

internet

- foley sounds


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Sounds Impact on Image

High pitch = tension, suspense

Low pitch = less tension, mystery

Loud sounds = intense, threateningQuiet sounds = delicate, hesitant

Fast tempo = more tension

Silence = highlights, isolates image, can

represent death, sticks out if a mistake


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Sounds Impact on Image !

Sound effects both atmospheric and diagetic

Off screen sounds can expand the film worldbeyond the frame

Sounds can be used like motiffs and servesymbolic functions

Sounds can be used as to aid transitions and

foreshadow action


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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

principles of sound

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