A natural sounds is that of an actual source. Natural sounds are unadorned production sounds. 

In film and television, many natural sounds do not meet everyone's expectations. When this happens, they are either replaced with more suitable sounds or the natural sound is layered (other sounds are added) to make it more desirable. 
 

• The actual sound item for a  .38 pistol will come off sounding like a "anemic" cap pistol.

• The  "dramatic ricochet" with gradually decreasing pitch is extensively used in film and TV (instead of all other possible ricochet sounds)

Our perception of natural sounds has become so influenced by ideology about sounds  that we are often disappointed with reality.  
 

Characteristic sounds  

A characteristic sound is what a sound should be according to someone's perception of the sound.  

When a natural sound is manipulated to achieve a desired effect, it becomes characteristic. 

To satisfy either personal dictates or production demands sound effects have to.... 

• be recognizable
• meet audience expectations

All Sound effects may be grouped in one of two categories; natural or characteristic. 

David Bordwell and Kristin Thompson use the term  "fidelity"  
Fidelity refers to the extent to which the sound is faithful to the source as the audience conceive it. 

A possible term for this phenomena is "contract of convention"  (I used the latter in my article  "Synchresis" in  Filmhäftet 94/4) 

• Robert L Mott, Sound effects, radio, TV, and Film (p 73 - 86) 

Film Sound Design    www.filmsound.org       Oxford University: "...an excellent collection of resources and links.."