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The Purpose of Sound effects

The function of sound effects is three fold...[1] 

Simulating Reality  

In a western barroom fight our hero is hit over the head with a whiskey bottle.  
    The bottle is fake. It becomes real with the addition of an actual glass bottle crash from the sound editors library.   In gun battles the weapon actually is actually loaded with blanks and what is called quarter loads which means one-fourth of normal amount of gunpowder contained in a real bullet. The actual sound is just slightly louder than a cap pistol until the sound editor has completed work. 
These are but two of the more obvious examples of the sound effect taking a fake bit of theatrics and making it real by adding a real sound.   

You see it - you hear it - you must believe it!    

Creating illusion  

Creating illusion was one of the biggest additions to the art of film by sound.    

A man and a woman walk into a café. Several other people are sitting at various table in deep conversation. The main couple sits at a table and a series of close ups for their conversation are presented.    
    By adding the sound of the off-scene diners the audience is convinced that they are still in the café. Obviously, the producer does not want to pay a group of extras to sit off camera. The sound editor places them there with his crowd walla for the sound  (Walla is an industry term for the sound of people talking without hearing specific words)  

A woman is sitting in her living room. The door opens and her husband walks into the room.  
    With the addition of a few sound effects, it is possible to inform the audience that he has driven up to the house, parked his car, walked to the door, and used his key to unlock the door. None of this was shot. It was an illusion created with effects. 

A safari makes it through the jungle  
    The sound editor cuts a lion roar. Not has he placed a lion in the film where none exists but he has also placed the safari in danger.   

A cowboy sits around a small campfire. The mood of a campfire is warm.    
  • Add an off-scene owl and it becomes lonesome. 
  • Add a wolf howling in the distance and it perhaps harken danger. 
  • Cut a gunshot and you are telling the audience that another human is nearby. Is he friend or foe? 
Anticipation, possible danger, fear, joy - all are being evoked. Which should you be feeling? Move forward in your seat because surely the film will soon tell.  

A pair of lovers is caught in the midst of an argument. Suddenly, the woman turns, walks to the phone, and lifts the receiver.   
  • You can cut the first phone ring just ahead of the reaction and there is nothing unusual. 
  • Cut two or three rings before she reacts and you are telling the audience that she was so involved in the argument she did not even react to the phone until the third ring. That is revealing about her mood and depth of involvement. 

A leading lady awakens in the morning snuggled in her bed.   
  • The sound of a distant train whistle make is a lonesome scene. 
  • Replace the train whistle with the sound of kids playing outside, and the audience perceives an entirely different emotion 

The leading man drives up to a house.    
  • As he parks, we hear the sound of a small dog yapping. No particular danger is perceived. Inside is probably a child or an old lady. 
  • Change the small dog yapping to the sound of a vicious Doberman, and the mood is again changed. 
The sound effect is a major part of the magic of Hollywood. The plywood wall becomes real when the sound of a big wood crash is added. The avalanche of large boulders (actually foam rubber or styrofoam is) real and menacing because of the sound effect.  
The sound effect is not only a mechanical tool ( e. g., fire a gun, cut a shot), it can also be employed creatively and artistically.    

1. In his text M Kerner also makes the conclusion that
effect = illusion + mood (page 12) 

I use a variant of M Kerner's when I teach film sound
Functions of film sound:  illusion &  narration

Edited excerpts from  Kerner, Marvin M: The Art of the Sound Effects Editor (1989),  
p 11- 15 
     Oxford University: " excellent collection of resources and links.." 




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