A term used in radio, film, and television sound recording to describe the murmur of a crowd in the background. A group of voice actors assembled in a post-production studio to create this sound effect is commonly called a walla group. According to legend the term was coined in the early days of radio, when it was found that engaging several people to repeat the nonsense word “walla” was an effective substitute for the indistinct chatter of a crowd. (Other practitioners, particularly in the UK, use the word “rhubarb”, which is another name for this technique.) Now, walla actors frequently make use of real words and conversations, often improvised, tailored to the languages, speech patterns, and accents that might be expected of the crowd to be mimicked.