Listed below are nine components that most influence how sound effects are perceived. By modifying or eliminating any one or a combination of these components, the sound effects are changed or totally new sounds are created.  

"Music components":   

• Pitch 
• Timbre
• Harmonics
• Loudness
• Rhythm

• Attack
• Sustain
• Decay

• Speed 

Envelope of sound and Speed: 

• Sound design of an atomic bomb detonation

Pitch  

The pitch of a sound is determined by the frequency of the sound. Normally we refer to its pitch.   

Frequencies are grouped as ..  

• low (bass) - sounds of thunder and gunshots
• midrange - a telephone ringing
• high (treble) - small bells and cymbals

  
  
• Low frequencies make the sound powerful and warm

• Midrange frequencies give sound its energy. 

Humans are most sensitive to midrange frequencies.

• High frequencies give a sound its "presence" and life like quality. Presence of a sound enables us to hear it clearly and gives us the feeling that we are close to its origin.

Timbre is that unique combination of fundamental frequency, harmonics, and overtones that gives each voice, musical instrument, and sound effect its unique coloring and character.  
  

When a object vibrates it propagates sound waves of a certain frequency. This frequency, in turn, sets in motion frequency waves called harmonics.  

The basic frequency and its resultant harmonics determine the timbre of a sound. The greater the number of harmonics, the more interesting is the sound that is produced.  

It is an object's ability to vibrate and set up harmonics that determines the  pleasantness of the resultant sound. Crystal glass set up harmonics that are more pleasant than harmonics of ordinary glass.  

The combination of fundamental frequency and its harmonics is a complex wave form.  
  

Loudness  

Loudness becomes meaningful only if we are able to compare it with something. The sound of a gunshot may be deafening in a small room, but actually go unnoticed if fired in a subway station when a train is roaring past.  

(A film that use this in the narrative is Sleepers - when a man is shot at the same time as an aircraft is landing) 

"Equal loudness"   
Humans are most sensitive to frequencies in the midrange (250 Hz - 5000 Hz)   

When two sounds, a bass sound and a middle range sound are played at the same decibel, the listener perceive the middle range sound to be louder.  

This is why a clap of thunder in a horror movie may contain something  so unweatherlike as a woman's scream.  
 
 

Wooden pegs, suspended by wires in a wooden frame to suggest the sound of a large group of people marching in order, will be believable if correct rhythm is supplied. If the rhythmic cadence were ignored the wooden pegs would sound like wooden pegs drummed mechanically on a wooden surface. 
 

Attack 

There are two types of attack: 

• fast
• slow

Sounds that have a fast attack are.. 

• gunshots
• slaps
• door slams

Sounds that have a slow attack are… 

• a dog's short warning growl prior to bark
• stepping on a dry leaf
• slowly tearing a sheet of paper
• closing a door slowly
• an entire thunderclap

The entire thunderclap has a time span of approximately five seconds.   By starting the sound at point A, the audience is prepared for the impending thunderclap.   To have a frightening sudden clap of thunder, the slow attack has to be changed to a fast attack.

Manipulating the sustain time of a sound is yet another way of either modifying a sound or create a totally new one. 

Suppose you got a the sound of an elevator starting, running, and stopping, all within 25 seconds, but the script calls for a scene to be played in an elevator that runs for 60 seconds. Edit the sustain portion - make a it into a loop.  (If you got a computer just copy and past) Take care to avoid sudden burst of level changes. 

Decay 

The decrease in amplitude when a vibrating force has been removed is called decay. The actual time it takes for a sound to diminish to silence is the decay time. How gradual this sound decays is its rate of decay. 

Listening to a sound tells if it is... 

• Indoors (small enclosed area with a great deal of absorbency)

- little decay  and with very little or no reverberation 

• outdoors (open unconfined area)

- long decay with an echo 

An advice: 
- When ever you are editing a sound, you must allow enough room at the tail for fade. (This includes sound on Internet!!!) 

Speed 

Played at twice as fast as the recorded speed .. 

• a explosion will sound like a gunshot
• a voice will sound like the cartoon chipmunk character

The accompanying sound should convincingly match the magnitude of the explosion and the seeming deliberate amount of time it take for the cloud to take shape.

What sound  will match ... 

• the roaring power?
• the loudness or the attack?
• the inordinately long sustain and decay?  

Sustain and Decay 
- roar of a huge waterfall 

Speed 
-  dynamite explosion and  waterfall roar [1] at slow speed  
 
In utilizing the components of a sound to create other sounds, the step that must be taken is disassociating the names of the sound with the sounds themselves. Although there are millions of names for sounds, the sounds themselves all fall into certain frequency parameters that can be manipulated by the nine components of sound.  

Therefore, the fact that waterfall record was selected is of no consequence. One sound of waterfall is much the same as any other waterfall sound. The only thing that are interesting in as far as sound effects are concerned is the magnitude of the waterfall - its roaring power. (The actual sound source may even be a train roaring through a station.) 

Because this sound offer no identification other than a constant roar it can readily be adapted for other sounds.  

When a believable sound is matched to a picture there is never any doubt in anyone's mind that the sound is not authentic. If the sound is a shade to fast or slow, it will cause many viewers to think that "something" was not quite right.  

Not one viewer, not one critic, not even the scientists who actually developed the bomb complained about this odd mixture of sounds when they appeared on the TV news in the early 1950s. What everyone heard matched convincingly the picture. 

One aspect of this audiovisual phenomena is  synchresis.   

1. A record was slowed from 78 rpm to approximately 30 rpm.   
The basic principle behind this is to slow a sound to the point where it is basically a tone of indistinct noise. 

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