sound

NOTE: here is a good example of a film ( pulp fiction) which has been re-edited into a silent movie , to demonstrate how absence of diegetic sound can add to the overall atmospheric effect.
http://www.youtube.com/watch?v=liUuzHK7kBY&feature=player_detailpage

Diegetic sound

Diegetic sound is audio which is visible or whose source is implied to be

present by the action of the film.This can be shown by the voices of the characters,

sounds made by objects or music which is shown coming from a particular source

e.g. a piano or radio would be good evidential basis.

http://www.youtube.com/watch?v=fRI15yhjeNQ&feature=player_detailpage
Here is a link of a nighhclub scene which has added diegetic music to emphasize this.

Non diegetic sound

This form of sound is the relative opposite of diegetic as this is audio which is not

visible on screen and cannot be seen coming from a source. Examples of non- diegetic sound is that such as the narrators commentary, sound effects or 'mood music' which effectively tells the audience what tone the film is supposed to portray e.g. Happy.
http://www.youtube.com/watch?v=l650hWV1Vhk&feature=player_detailpage
Above is a link of a 36 second clip which has added non-diegetic sound

Synchronous Sound

Synchronous sound is synchronized with what is visible on screen. For example if the film shows a character playing the piano then the sound is projected. It also creates a sense of realism e.g. ' click' of a door may simply be used to convince the audience of the authencity of the imagery.

http://www.youtube.com/watch?v=0uJkN5n0v4U&feature=player_detailpage
This is described as the first attempt at synchronous sound in 1899 which would be intriguing to compare to modern society technology.

Asynchronous sound

This collective term is where sound effects are not matched with the apparent source

 of  visible sound. This is to essentially provide emotional basis to the piece. As an

example, there are people in the background arguing and in the background is the sound of sirens.This indicates that perhaps they have committed a crime or something is about to happen to them.
http://www.youtube.com/watch?v=LzAoCsvvFBY&feature=player_detailpage

This is an example of this technique within a film called 39 Steps where you see the woman screaming but the train whistling at the same time.

Sound effects

Sound effects are artificially enhanced sounds which emphasize the artistic content of films, TV, live performances, animation, video games, music and other media.

http://www.youtube.com/watch?v=1PZLebGqOP8&feature=player_detailpage
This clip is of someone playing the piano which has usage of artificially enhanced sound enablement

Sound motif

A sound motif is a sound effect or combination sound effects which are associated

 with a particular character, setting, situation or idea.

http://www.youtube.com/watch?v=RQ_RuxPxMXY&feature=player_detailpage
Here is a sound motif from the movie Jaws. Every time the shark is introduced or about to come on screen the sound begins.

Sound bridge

Use of this method enables addition of continuity through sound by running either

narration , dialogue or music from one shot across a cut to another shot.
http://www.youtube.com/watch?v=uQfzvVeEkGI&feature=player_detailpage#t=145s

At 2.29 I have included the URL from I am Legend which shows the haunting music carrying on into the next scene with the enablement of a completely differential location.

Voice over

This is a production technique where a non diegetic voice is broadcast either live ,

 is pre-recorded in Radio/ TV/ Film/ Theater or presentation. It can be spoken by a

specialist voice actor or could be spoken by someone who appears on screen.
http://www.youtube.com/watch?v=tcnioEOMKMM&feature=player_detailpage#t=37s
Here I have entailed the inclusion of Twilight's actress Bella ( Kristin Stewart) who has a voicover over a footage of deer, frolicking in the grass.

Ambient sound

This formula entails the consistence of noises present in the environment

which pertains the pervading atmosphere. The term ambience derived from

this terminology is used in background sounds which are either present in the

 original production recording or deliberatlly added in the editing of sound effects

in order to provide an acoustic space around the remainder of the dialogue and

 sound effects.

http://www.youtube.com/watch?v=utlbZR4mj08&feature=player_detailpage
Here is a link which has 5 samples of ambient sound