How does film film achieve the synchronization of image and sound?

The sound playback of audio movies is called playback, which means that the recorded sound is restored and played, and playback can be divided into two ways.

First, the sound returns from light, that is, the sound signal is converted into an electrical signal and then into an optical signal, which is printed into a film picture. During screening, the vocal cords are illuminated by the excitation lamp and projected onto the photovoltaic cell. The photovoltaic cell senses the intensity of light and converts it into a variable electrical signal, which is amplified by the amplifier into a sound signal and played by the speaker. When the film is running, it first passes through the shutter and is irradiated by excitation light at the sound drum, so the picture and sound are not parallel in the printing process, but the phase difference is 16, so that the picture playback and sound can be synchronized.

Extended data:

35 mm and 16 mm sound movies generally use light playback.

The second is magnetic echo. Think about the tape recorder. The magnetic stripe is printed on one side of the film screen. In order to achieve synchronization, the screen is also advanced 16. When the film is running, the image is taken through the film door first, and then the sound is made through the magnetic head. Early 16 mm film used magneto-acoustic reproduction, but rarely. As a feature of China, 8.75mm films all adopt magnetic echo. The sound quality of magnetic amplifier is better than that of optical amplifier.

Because the picture and recording signal are printed on the film, they appear synchronously when the film is running, and there is no influence when changing the film.