Sound effects or audio effects are artificially created or enhanced sounds, or sound processes used to emphasize artistic or other content of movies, video games, music, or other media.
In motion picture and television production, a sound effect is a sound recorded and presented to make a specific storytelling or creative point without the use of dialogue or music. The term often refers to a process applied to a recording, without necessarily referring to the recording itself. In professional motion picture and television production, the segregations between dialogue, music, and sound effects recordings are quite severe, and it is important to understand that in such contexts dialogue and music recordings are never referred to as sound effects, though the processes applied to them, such as reverberation or flanging, often are.
The use of sound effects originated in theater; by some accounts sound effects were already in use in Classical Antiquity. Various devices were used to simulate such sounds as thunder or approaching horse hooves off stage. The repertory of early theatrical sound effects became more elaborate in the early modern era, and various mechanical devices were constructed to produce more and better sounds. Large urban theaters often had large collections of such devices. Samples of such vintage sound effects can occasionally be heard in early audio recordings of Vaudeville acts, although by contemporary accounts the effects in the primitive early recording studios were less elaborate than those in theaters.
The field of sound effects advanced considerably in the 1920s, first with the impetus of radio. Most early radio was live, and featured many live theatrical productions which made much use of sound effects. The better radio studios often employed several sound effects men working at the same time on productions. In the mid 1920s, the advances in recording technology with improved electronic microphones allowed for the practice of having pre-recorded repertories of sound effects on 78 rpm records. Actual recordings of motorcars, airplanes, large crowds laughing or shouting, etc. could then be added to radio dramas via the discs. In the late 1920s motion picture studios switched from silent film to sound, opening up another venue for sound effects.
In the context of motion pictures and television, sound effects refer to an entire hierarchy of sound elements, whose production encompass many different disciplines, including:
Hard sound effects are common sounds that appear on screen, such as door slams, weapons firing, and cars driving by.
Background (or BG) sound effects are sounds that do not explicitly synchronize with the picture, but indicate setting to the audience, such as forest sounds, the buzzing of fluorescent lights, and car interiors. The sound of people talking in the background is also considered a "BG," but only if the speaker is unintelligible and the language is unrecognizable (this is known as wall). These background noises are also called ambience or atmos ("atmosphere").
Foley sound effects are sounds that synchronize on screen, and require the expertise of a Foley artist to properly record. Footsteps, the movement of hand props, and the rustling of cloth are common Foley units.
Design sound effects are sounds that do not normally occur in nature, or are impossible to record in nature. These sounds are used to suggest futuristic technology, or are used in a musical fashion to create an emotional mood.
Each of these sound "food groups" are specialized, with sound editors known as specialists in an area of sound effects (e.g. a "Car cutter" or "Guns cutter").
The process of creating sound effects can be separated into two steps: the recording of the effects, and the processing. Large libraries of commercial sound effects are available to content producers (such as the famous Wilhelm scream), but on large projects sound effects may be custom-recorded for the purpose.
Also, if the soundtrack is processed through a Foley, it can make the smallest sound look perfect on screen and the audience can never guess how much work went into the making of that specific sound.