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Chapter #2

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What is Sound

Sound is the vibration as perceived byHearing.

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Hearing your Own Voice

Only you hear your voice the way you do. Everyone else

hears your voice differently. This is because Sound Wavesinside your body travels through the bones, cartilage &muscles between your voice box & your inner ear { you hearyour self through your body}. While other people (or sound

from tape records)

travel through the air & reach youreardrum. { hears the voice through air }.

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Use Audio in Multimedia

You use sound in a multimedia project in 2 ways. In fact, allsounds fall into 2 broad categories:

1. Content Sound.

2. Ambient Sound.

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Content Sound

Content Sound provides information to audience.* e.g. Dialogs in Movies or Theater.

Types of Content Sound:

1. Narration : provides information about an animation that is playing on thescreen.

2. Testimonials : these could be auditory or video sound tracks & used inpresentations or movies.

3. Voice- Overs : used for short instructions, e.g. to navigate the multimediaapplication.

4. Music : may be used to communicate (as in a song).

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Ambient Sound

Ambient Sound consists of an array of background & soundeffects.

Types of Ambient Sound:

1. Message reinforcement :The background sounds you hear in real life.Such as crowds in a ball game, can be used to reinforce the message that you

wish to communicate.

2. Background Music : Set the mood for the audience to receive & processinformation by starting & ending a presentation with music.

3. Sound effects :are used in presentations to liven up the mood & add effectsto the presentation. such as sound attached to bulleted list.

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Frequency

Frequency: The number of peaks (crests) that occur in onesecond.

Frequency is Measured by the number of cycles(vibrations

)per second.

The Unit of Frequency is hertz (Hz).

Human can perceive a range of frequencies from 20-20,000Hz(or 20 kH). However its most sensitive to sounds in the

range of2-4 kHz.

Period : The difference in time between the formation of 2 crests.

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Ampli

tude

Period Crest

TroughDuration (Time in Second )

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Wavelength : is the distance from the midpoint of one crest tothe midpoint of the next crest.

-its represented by the symbol :

Bandwidth : the difference between the highest & the lowest

frequency. {BW = highest freq. - lowest freq. }

DopplerEffect: Compressions & rarefactions of air.- e.g. When the object making the sound is moving toward you, the frequency goesup due to the waves getting pushed more tightly together. The opposite happens whenthe object moves away from you & the pitch goes down.

- When the making sound object moves toward you, the pushes of sound -soundwaves- Get Crammed Together. which makes them higher pitched.

- When the making sound object moves away from you, the sound waves are SpreadOut Further apart. That makes a lower pitched sound.

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Doppler

Effect

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Velocity of Sound The Velocity of sound may be found by measuring the time

required for the waves to travel a measured distance. Thevelocity varies greatly with the medium through which ittravels.

The Velocity of sound increases as the temperature rises. Anddecreases as the temperature falls.

V= d_t

T= d_v

D= t*v

Air 331.5

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(= Rahma Alhajri =)

Saturday December 22 12