Audio recorded magnetically on film or tape stock — superior to optical sound, easier to master and re-record. Industry standard for theatrical 16mm and 35mm.
Magnetic Sound
You will encounter magnetic sound on almost every set when working with film — especially in the documentary field or on productions still shooting on analog material. The technique uses magnetic induction: sound waves are converted into electrical signals, which are then recorded onto a magnetized layer. This can happen on special magnetic tapes or directly onto the filmstrips themselves — so-called fullcoat or striped film. The decisive advantage over optical sound: you have lossless recording, no degradation from exposure, and the dynamic range is preserved.
In practice, this means for you on set: magnetic sound devices — Nagra, Stellavox, later digital recorders — deliver a clean, uncompressed recording. In contrast to optical sound, which has to be printed and inevitably loses quality in the process, here you store purely magnetically. This makes magnetic sound particularly valuable for synchronization and later post-production. You can record multiple tracks in parallel, editing later without the constraint of a low-pass filter. Magnetic sound was long the standard, especially in the 16mm domain — for documentaries or smaller productions, for instance — because the technical hurdle is low and the quality is good.
A practical point: magnetic sound requires storage and handling. Magnetized materials are susceptible to magnetic field interference and moisture changes — you store magnetic tapes cool and dry, not next to radio communication devices. During editing, you then work with contact copies or already digitized material; the original magnetic sound masters remain in the archive. Mastering — the transfer to optical sound or later to DCP — is done from this clean, uncompressed source. This gives you significantly more leeway in EQ and dynamics processing than with the direct optical original. Many archive and restoration projects rely precisely on old magnetic sound masters for this reason: the source quality is often better than the optical copies that were made later.