noun plural
: effects that are imitative of sounds called for in the script of a play, radio or television program, or motion picture and are produced by various means (as phonograph records, musical instruments, or mechanical devices)
before radio began to grow up in the 1920s, the technique of sound effects was extremely limited — Richard Hubbell
a sound-effects girl … making radio noises like fire trucks, kisses, waterfalls, telephones — Harper's