Dolby also searched to develop film sound. The company’s history writes:
Upon investigation, Dolby found that many of the limitations in optical sound stemmed directly from its significantly high background noise. To filter this noise, the high-frequency response of theater playback systems was deliberately curtailed… To make matters worse, to increase dialogue intelligibility over such systems, sound mixers were recording soundtracks with so much high-frequency pre-emphasis that high distortion resulted.
A Clockwork Orange (1971) was the first film with Dolby sound that utilized Dolby noise reduction on all pre-mixes and masters, but with traditional optical soundtrack on release prints. Callan (1974) became the first film with a Dolby encoded optical soundtrack. In 1975 Dolby introduced Dolby Stereo including a noise reduction system as well as more audio channels (it could have additional center and surround channels matrixed from the left and right). The first film with A Dolby – encoded stereo optical soundtrack was Lisztomania (1975), but it was only made in an LCR (Left-Center-Right) encoding technique. The first movie containing the true LCRS (Left-Center-Right – Surround) encoded soundtrack was called A Star is Born in 1976. Having reworked the system a bit for home viewing, Dolby released Dolby Surround, which only extracted a surround channel, and the more advanced Dolby Pro Logic, which actually was the domestic counterpart of the theatrical Dolby Stereo.
Dolby engineers also developed a digital surround compression scheme for the movie. Dolby Stereo Digital (now simply known as Dolby Digital) was first encoded on the 1992 film Batman Returns. Another Dolby format, AC-3 (the film Clear and Present Danger was offered at the home theater market on a laserdisc in 1995) did not make much profit in the consumer market and eventually became part of the DVD specification. Dolby Digital was included in the High Definition Television (Advanced Television Systems Television, HDTV and ATSC respectively) standard of the USA, DVD-players, and a lot of satellite-TV and cable – TV receivers. TV series The Simpsons used the Dolby digital surround sound compression scheme.
In 2005, the corporation offered its shares on the New York Stock Exchange, claiming to become public under the symbol DLB. The same year it celebrated the 40-anniversary.