Movies made sound with a light bulb: Sound-on-film
Technology Connections・31 minutes read
The teacher utilized a 16mm film projector for an audio-visual experience, showcasing the technology and mechanics involved in projecting films. The evolution from traditional film projectors to digital surround sound systems like Dolby Digital and DTS revolutionized the cinema experience, enhancing sound quality and simplifying projection processes.
Insights
- The use of a Bell & Howell 16mm film projector by the teacher to show a movie highlights the importance of audio-visual experiences in educational settings, bridging the gap between visual and auditory learning through synchronized soundtracks and still image projection.
- The evolution of film technology, from the mechanical intricacies of the 16mm projector's film advance mechanism to the advancements in sound-on-film processes like Dolby Stereo and DTS, showcases the continuous innovation in cinematic experiences, emphasizing the transition from manual film handling to digital surround sound systems that revolutionized the industry.
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Recent questions
How does a 16mm film projector work?
A 16mm film projector projects still images rapidly to create the illusion of movement. The film advance mechanism moves the film one frame at a time, with a rotating shutter blocking light during movement. Each frame is displayed three times per second, reducing flicker by flashing the image 72 times per second. Threading the film involves passing it through sprockets and roller guides for smooth movement. An optical sound-on-film process reproduces sound, with a light sensor generating a signal from changes in brightness on the soundtrack. The soundtrack is read by an exciter lamp, generating a signal that can be amplified.
What is the purpose of cue marks on film reels?
Cue marks on film reels signaled projectionists to switch projectors for seamless viewing experiences. Projectionists had to quickly switch projectors during changeovers, unloading the first projector, threading the next reel, cueing it up, and rewinding the first reel if they had a separate rewinder. The introduction of large platter systems allowed entire films to be stored spliced together, eliminating the need for rewinding and enabling projectionists to manage multiple screens simultaneously.
How did the introduction of digital surround sound impact film technology?
The introduction of digital surround sound in the '80s required an update to sound-on-film technology. Dolby Stereo offered basic surround sound starting in 1976, with different formats like Dolby Digital, Sony Dynamic Digital Sound (SDDS), and Digital Theater Systems (DTS) emerging. DTS utilized a timecode on special CD-ROMs to identify the film playing and the exact time of the projected frame, simplifying scanning equipment but requiring additional off-projector hardware. The shift to digital surround sound contributed to the decline of SDDS in cinemas.
What is the function of the flywheel in a film projector?
The flywheel in a film projector is attached to the sound drum and functions similarly to a capstan in a tape recorder. It helps thread the film smoothly and maintains a consistent speed to prevent flutter. The rotating mass of the flywheel smooths out variances in film speed, ensuring a steady projection.
How does a film projector reduce flicker during projection?
A film projector reduces flicker by displaying each frame three times per second, flashing the image 72 times per second. This rapid display creates the illusion of continuous movement. The rotating shutter in the projector blocks light during film movement, contributing to a smoother projection without flicker.
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Summary
00:00
"16mm Film Projector: Audio-Visual Experience"
- The teacher decides to show a movie due to a hangover, using a Bell & Howell 16mm film projector.
- The 16mm film projector can project images and play synchronized soundtracks, creating an audio-visual experience.
- 16mm film was commonly used for television, industrial, and educational films, sitting between 8mm and 35mm formats.
- The film projector projects still images rapidly to create the illusion of movement, requiring each frame to be still while projected.
- The film advance mechanism in the projector moves the film one frame at a time, with a rotating shutter blocking light during movement.
- The projector displays each frame three times per second, flashing the image 72 times per second to reduce flicker.
- Threading the film through the projector involves passing it through sprockets and roller guides to maintain smooth movement.
- The projector uses an optical sound-on-film process to reproduce sound, with a light sensor generating a signal from changes in brightness on the soundtrack.
- The soundtrack on the film is read by an exciter lamp, with the light sensor behind a sound drum generating a signal that can be amplified.
- The sound drum, similar to a capstan in a tape recorder, is attached to a flywheel inside the projector for threading the film.
14:55
Film threading and sound modulation techniques.
- The rotating mass of the flywheel smooths out variances in film speed to prevent flutter.
- Spring-loaded rollers maintain tension on the film to keep it in contact with the drum.
- Floating rollers absorb slack from the sprocket's jittery turning for smooth film movement.
- Proper threading involves slipping the film under the sprocket with precise tension.
- The sound signal on the film is modulated using the variable-area technique.
- An exciter lamp projects a precise slit of light onto the film for accurate signal reproduction.
- 16mm film moves at slightly over seven inches per second, affecting sound fidelity.
- Dual-bilateral variable-area soundtracks reduce azimuth distortion for better sound capture.
- Mirror galvanometer devices create wiggly waveforms on photographic film for sound.
- Cue marks on film reels signaled projectionists to switch projectors for seamless viewing experiences.
30:09
Evolution of Film Projection Technology
- Projectionists had to quickly switch projectors during changeovers, unloading the first projector, threading the next reel, cueing it up, and rewinding the first reel if they had a separate rewinder.
- The upgrade to large platter systems allowed for entire films to be stored spliced together, eliminating the need for rewinding and enabling projectionists to manage multiple screens simultaneously.
- The introduction of digital surround sound in the '80s required an update to sound-on-film technology, with Dolby Stereo offering basic surround sound starting in 1976.
- Different sound formats like Dolby Digital, Sony Dynamic Digital Sound (SDDS), and Digital Theater Systems (DTS) emerged, each with varying bitrates and methods of encoding audio.
- DTS utilized a timecode on special CD-ROMs to identify the film or trailer playing and the exact time of the projected frame, simplifying scanning equipment but requiring additional off-projector hardware.
- The DTS system, like Dolby Digital, was a 5.1 channel system, providing a similar experience for producers and contributing to the decline of SDDS in cinemas.
