Sound
Have you ever watched a movie at home with the sound muted? It is amazing what a difference the sound makes. The music, noises and dialogue make it easier to understand what is happening. Most movies would be a lot less interesting if you took away the sound.
Most 35 mm movies have the sound encoded on the film. It is called "optical encoding." A transparent line is recorded along one side of the film. This line changes its width according to the frequency of the sound. As the film passes the audio pickup, a lamp shines a bright light through the line. The light that passes through the film shines on a photocell.
The photocell changes the light to electrical current. The wider parts of the line allow more light, which causes the photocell to produce more current. Since the width of the transparent line changes the amount of light, you get a variable electric current that can control a pre-amplifier. The pre-amplifier boosts the signal and sends it to a huge amplifier, which distributes the signal to the speakers.
Most films today use the Dolby Digital system to improve the sound. The DD reader mounts on top of the projector (some projectors now have the reader built right in) and scans the film as it passes through. Light from an LED shines through the film onto a CCD. The image, containing little specks that represent 1s and spaces that represent 0s, is sent to a special computer that turns the binary data back into sound. So there are two optical tracks (running along the side of the film) and the Dolby Digital track (stored between the sprocket holes).
Dolby Digital creates six tracks of sound:
- Center (plays from the center of the screen)
- Left (plays on the left side of the screen)
- Right (plays on the right side of the screen)
- Left surround (Plays from speakers on the left wall)
- Right surround (plays from speakers on the right wall)
- LFE (low-frequency effects) (plays from a big subwoofer)
This configuration is commonly referred to as 5.1, for five main channels plus an effects channel. The effects channel uses a subwoofer and is often called the boom channel because its main use is for explosions and other powerful, teeth-rattling sounds.
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Tomlinson Holman's eXperiment
You see it at lots of movie theaters, and at the beginning of many DVDs. It is the THX logo. What does it mean for something to be THX certified?
THX is named after THX 1138 (George Lucas' first feature film) and THX inventor, Tomlinson Holman. In a movie theater, THX means that people have inspected the movie theater to make sure that there are no distractions. They have checked to make sure that there is no noise leaking in from the theater next door or from the concession stand. They make sure the air conditioner and the projector are quiet. They make sure that the theater does not echo, that the image on the screen is bright enough, that the screen is the right size for the theater, and that everyone in the theater can see the screen. They also make sure the sound system has enough power, and enough speakers, to bathe the whole theater in sound. Finally, they add a piece of THX equipment (called a crossover network) to the sound system to make it work better. By making sure that everything in the theater is perfect, THX gives you the best movie experience possible.
You can find THX logos in the home as well, on DVDs, video games, receivers and speakers, which means they've all been tested and engineered to THX standards.
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