ISO 490:1993

Overview

ISO 490:1993 is an international standard developed by the International Organization for Standardization (ISO) that specifies the positions and width dimensions for magnetic stripes and magnetic recording head gaps used in sound recording on 16 mm motion-picture film perforated along one edge (Type 1). This standard is essential for maintaining uniformity and compatibility in cinematography equipment and film production, ensuring high-quality magnetic sound recording and playback.

The document addresses key parameters such as the location and width of magnetic striping, the dimensions of magnetic head gaps, film projection speed, and longitudinal picture-sound displacement. ISO 490:1993 replaces the earlier 1978 edition, incorporating technical revisions vital for modern film and sound processes.

Key Topics

• Magnetic Striping Location and Width
  The standard defines the exact positioning of the magnetic sound stripe on 16 mm film. The stripe is applied on the side toward the projector lamp for direct projection on reflection-type screens. A balance stripe may be added if the magnetic stripe increases film thickness beyond 0.005 mm to ensure even thickness across the film edges. The maximum acceptable thickness for magnetic and balance stripes is 0.020 mm.

• Magnetic Recording Head Gaps
  Specifies the precise location and width of the magnetic recording head gaps, critical for accurate sound recording and playback. The effective head gaps must be at a right angle (90° ± 5') to the film's longitudinal axis to maintain sound quality.

• Film Projection Speed
  Film projection speeds are detailed for different applications, including professional (cinematography and television) and non-professional use. The primary standards specify speeds of 24 frames/s for cinematography and television (50/60 Hz supplies), while secondary standards recognize slower speeds such as 18 frames/s for non-professional equipment.

• Longitudinal Picture-Sound Displacement
  The magnetic sound recording on the film should precede the corresponding picture center by 28 ± 1 frames, ideally 28 ± 0.5 frames, to synchronize audio with visual content accurately.

Applications

ISO 490:1993 is critical for multiple fields within the motion picture and audiovisual industries:

• Film Production and Post-Production
  Ensures standardized application of magnetic sound stripes on 16 mm film stock, facilitating consistent sound recording quality and compatibility between different production and playback equipment.

• Film Projection and Exhibition
  Defines projector head gap positioning and film speed to ensure fidelity in sound reproduction during film screenings.

• Broadcast and Television
  Supports television standards involving magnetic sound recording on 16 mm film, especially adapting for 50 Hz and 60 Hz frequency supplies in different regions.

• Equipment Manufacturing
  Provides technical specifications for manufacturers producing magnetic recording heads, projectors, and editing machines compliant with international norms.

• Archiving and Restoration
  Helps archivists accurately preserve and restore audio tracks on historical 16 mm film reels by following internationally recognized positioning and dimension guidelines.

Related Standards

ISO 490:1993 references and complements several other ISO standards relevant to cinematography and film handling:

• ISO 69:1990 – Cinematography - 16 mm motion-picture and magnetic film - Cutting and perforating dimensions. Defines film perforations crucial to proper striping and head alignment.

• ISO 359:1983 – Cinematography - Projectable image area on 16 mm motion-picture prints - Dimensions and location. Specifies the picture frame area for synchronization.

• ISO 1188:1984 – Cinematography - Recorded characteristic for magnetic sound on full-coat 16 mm motion-picture film - Specifications. Details sound recording parameters ensuring audio quality aligns with this standard’s guidelines.

• ISO/TC 36 (Technical Committee on Cinematography) – The coordinating body responsible for the development and maintenance of this and related standards.

By adhering to ISO 490:1993, industry professionals ensure consistency, interoperability, and high-quality sound reproduction in 16 mm motion-picture films, fostering global standardization in cinematic sound recording technology.