Film strip coated with magnetic emulsion for audio recording — ran parallel to picture or striped directly onto celluloid. Pre-digital workhorse for sound editing.
For decades, magnetic film was the backbone of professional sound recording and editing in cinema. A plastic strip—usually made of polyester or celluloid—carried a thin layer containing iron oxide, which stored sound waves as magnetic impulses. Unlike optical sound, which was printed directly alongside the image, magnetic film ran synchronously with the picture film through the camera or editing suite, without the image and sound needing to be physically connected.
In practical workflows, this offered significant advantages. You could record multiple tracks simultaneously—magnetic film was available in 1/4-inch, 1/2-inch, or multitrack variants—and work completely independently in post-production. While the editor worked on the picture material, the sound mixer could arrange, resynchronize, or process their tracks with effects on separate machines. The magnetic film editing system was the standard solution until the 1990s: the sound editor worked with physical strips, splicing them onto reels, using magnetic film leader to test transitions. Adhesion was reliable, and quality was stable—as long as the magnetic layer did not wear out or get damaged by moisture.
The biggest problems were wear and storage. Over the years, magnetic film lost its adhesion, the layer could flake off, and moisture led to oxidation. Many archives lost valuable sound because the reels were not stored correctly. Handling was also labor-intensive—every cut, every rearrangement required manual splicing with magnetic tape.
With the digital revolution—DAW software (Digital Audio Workstations) like Pro Tools—magnetic film became obsolete. You could now work non-destructively in software, save unlimited takes, and set up automation. Digital formats took over. Nevertheless, anyone digitizing analog archives today or working with classic films will encounter magnetic film reels. Digitization is complex and expensive—and some sound mixers still swear by the sound of well-preserved magnetic films, the "warmer" tone compared to early digital codecs.