Overview
ISO 162:1985 specifies the location and width dimensions of head gaps for magnetic sound recording on motion-picture film. It covers three-, four- and six-track formats on 35 mm film (perforated per ISO 491) and a single-track format on 17.5 mm film. The standard also defines track assignment rules relative to the direction of film travel and practical guidance to ensure consistent recording and playback.
This standard is essential for manufacturers of magnetic heads, film laboratories, archivists and post-production facilities working with magnetic sound records on motion-picture film.
Key Topics
- Track formats covered: three-, four-, six-track on 35 mm; single-track on 17.5 mm.
- Head gap location and width: the standard defines precise positions and width dimensions (presented in figures and tables within the document) to ensure compatibility between recording and playback equipment.
- Track assignment:
- For monophony, the first recorded track is placed on track no. 1 across formats.
- For stereophonic layouts the standard specifies assignment conventions (e.g., left/center/right in three-track formats; four-track arrangements include an ambience channel). For six-track formats the assignment should be clearly indicated for each film due to varied practices.
- Head alignment: recording and playback head gaps must be aligned at 90° ± 3' to the film travel direction to maintain accurate azimuth and minimize crosstalk.
- Magnetic coating orientation: the magnetic coating must face up (surface magnetic side up) with respect to the indicated direction of film travel.
- 17.5 mm origin: 17.5 mm formats typically result from splitting 35 mm film; when split, the track adjacent to the perforation is designated track 1.
- Interchangeability note: metric dimensions in the tables are based on metric practice and may not be exact conversions; assemblies built to either system should be interchangeable for practical applications.
Applications
- Ensures compatibility between recorders and reproducers in theatrical and archival workflows.
- Guides manufacturers of magnetic heads and film sound equipment on head-gap placement and alignment tolerances.
- Supports film preservation and restoration by standardizing track assignment and orientation to avoid misinterpretation of recorded channels.
- Useful for post-production houses and dubbing facilities that handle multi-track magnetic film formats.
Related Standards
- ISO 491 - Cinematography: 35 mm film dimensions and perforation (referenced for perforation alignment).
- This edition replaces earlier ISO documents and consolidates technical revisions for consistent worldwide practice.
For implementation, consult the full ISO 162:1985 document for the detailed figures and tables that define exact head-gap positions and width dimensions.