Microphone Techniques

Optical Sound

The photographic or "optical" soundtrack was the first method of putting sound on film.  An opaque area adjacent to the picture contains narrow, clear tracks that vary in width with variations in the sound. [Doug Mitchell]

Magnetic Sound

In the 1950s, a new method of putting sound on film was introduced as an alternative to the optical soundtrack. After the picture is printed, narrow stripes of iron oxide material similar to the coating on magnetic recording tape are applied to the film (Figure 2). The sound is then recorded on the magnetic stripes in real time. In the theatre, the film is played back on projectors equipped with magnetic heads, similar to those on a tape recorder, mounted in a special soundhead assembly called a "penthouse." [Doug Mitchell]

The two main magnetic systems adopted were Twentieth Century Fox's four-track 35 mm CinemaScope system introduced for The Robe, and the six-track Todd-AO system first used for such 70 mm films as Oklahoma! and Around The World in 80 Days [Doug Mitchell]

dolby optical format led to the playback standard (ISO 2969). [Doug Mitchell]

In 1986, Dolby Laboratories introduced a new professional recording process called Dolby SR (spectral recording).

Dolby Laboratories puts a six-channel digital optical soundtrack in addition to a four-channel SR analog track on the same 35 mm prints

excerpts taken from "The Evolution of Dolby Film Sound" by Dolby Laboratories through Doug Mitchells MTSU homepage.

DTS:  lossy compression scheme.

Dolby Digital:  lossy compression.