Ele é chamado de " pista de risada ". Eles estão por aí desde os programas de rádio e são freqüentemente usados para levar o público a achar as piadas engraçadas.
Before radio and television, audiences experienced live comedy performances in the presence of other audience members. Radio and early television producers attempted to recreate this atmosphere by introducing the sound of laughter or other crowd reactions into the soundtrack.
Jack Dadswell (also known as the "Traveling Reporter" by Time Magazine), former owner of WWJB in Florida, created the first "laughing record".
In 1946, Jack Mullin brought a Magnetophon magnetic tape recorder back from Radio Frankfurt, along with 50 reels of tape; the recorder was one of the magnetic tape recorders that BASF and AEG had built in Germany starting in 1935. The 6.5 mm tape could record 20 minutes per reel of high-quality analog audio sound; Alexander M. Poniatoff then ordered his Ampex company to manufacture an improved version of the Magnetophon for use in radio production. Bing Crosby eventually adopted the technology to pre-record his radio show, which was scheduled for a certain time every week, to avoid having to perform the show live, as well as having to perform it a second time for West Coast audiences.
With the introduction of this recording method, it became possible to add sounds during post-production. Longtime engineer and recording pioneer Jack Mullin explained how the laugh track was invented on Crosby's show:
"The hillbilly comic Bob Burns was on the show one time, and threw a few of his then-extremely racy and off-color folksy farm stories into the show. We recorded it live, and they all got enormous laughs, which just went on and on, but we couldn't use the jokes. Today those stories would seem tame by comparison, but things were different in radio then, so scriptwriter Bill Morrow asked us to save the laughs. A couple of weeks later he had a show that wasn't very funny, and he insisted that we put in the salvaged laughs. Thus the laugh-track was born."
Amusingly, para alguns shows, você pode encontrar versões sem a faixa de riso e eu, pelo menos, regularmente encontrá-los menos engraçados sem. Aqui está um artigo sobre seu efeito nas reações do público.
A maioria dos seriados modernos são filmados em sets fechados, sem audiência ao vivo, então a faixa de risada é adicionada no post. No entanto, muitos shows costumavam ser gravados em sets abertos e grande parte do riso era de reações reais do público, embora muitas vezes foi reforçada / complementada com faixas gravadas.
Embora Charley Douglass tenha sido o criador e tivesse o monopólio da propriedade devido à propriedade da única máquina capaz de adicionar a pista de riso à fita, ele eventualmente perdeu o controle à medida que a tecnologia melhorava e os estúdios puderam replicar seu processo:Soon after the advent of the laugh track, Lucille Ball and Desi Arnaz devised a method of filming with a live audience using a multi-camera setup. This process was originally employed for their sitcom I Love Lucy, which used a live studio audience and no laugh track. Multi-camera shows with live audiences sometimes used recorded laughs to supplement responses. Sketch comedy and variety shows began to migrate from live broadcasting to videotape, which allowed for greater ease in editing during post-production. Editing a prerecorded live show with quadruplex videotape caused bumps and gaps on the soundtrack, Douglass was then called upon to bridge these gaps.
The Douglass laugh track became a standard in mainstream television in the U.S., dominating most prime-time sitcoms from the late 1950s to the late 1970s. By the 1980s, the Douglass family was eventually outrivalled by other sound engineers who created stereophonic laugh tracks different from the original analog track. Also, many single-camera sitcoms by this time started diverting from a laugh track altogether to create a more dramatic environment.
As faixas de risadas modernas são gravadas e arquivadas por designers de som e, muitas vezes, têm toneladas de faixas para escolher, de modo que possam ser adaptadas ao tipo específico de reação ao riso que o público deve ter.
Independentemente disso, há muito mais informações históricas sobre a trilha do riso e o uso de audiências ao vivo no artigo da Wikipedia, mas isso deve ajudá-lo a começar.