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 don’t • 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 don’t 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. 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

24. 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

25. 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