ISO 2404:1986

Overview

ISO 2404:1986 is an International Standard developed by ISO Technical Committee ISO/TC 36, focused on cinematography. This standard specifies the precise locations and dimensions of six-track magnetic sound records applied as magnetic stripes on 70 mm striped release prints of safety motion-picture film. It sets out the guidelines for the positioning and width of magnetic stripes and the alignment of magnetic recording and reproducing head gaps to ensure optimal sound quality and synchronization with visuals. The standard applies primarily to 70 mm safety film used in theatrical releases, establishing uniform criteria for consistent sound reproduction across cinema systems.

Key Topics

• Magnetic Stripe Locations and Dimensions
  The document details the exact placement and widths of six magnetic sound stripes on the 70 mm film strip. Each stripe corresponds to specific audio channels required for theatrical sound systems including left, center, right channels, and additional surround or monitoring signals.

• Sound Channel Assignments

  • Stripe No. 1: Extreme left channel
  • Stripe No. 2: Left central channel
  • Stripe No. 3: Central channel
  • Stripe No. 4: Right central channel
  • Stripe No. 5: Extreme right channel
  • Stripe No. 6: Auditorium loudspeakers or inaudible monitoring signals

• Head Alignment and Recording Angles
  Magnetic heads for recording and playback are required to be aligned with precise angular tolerances relative to film travel direction to ensure sound quality.

• Picture-to-Sound Displacement
  The magnetic sound tracks are offset behind the corresponding picture frame by 24 ± 1/2 frames to maintain audio-visual synchronization during projection.

• Reproducing Speed
  The sound tracks are designed for playback at 120 perforations per second, equating to 24 frames per second or a linear speed of approximately 34 meters per minute for standard cinema projection.

• Allowance for Film Shrinkage
  Tolerances account for lateral film shrinkage during production and playback to maintain dimension accuracy and alignment of magnetic stripes.

• Flexibility for Special Effects
  In special motion-picture films, the arrangement of stripes may deviate to achieve unique sound effects while maintaining overall compliance.

Applications

ISO 2404:1986 is essential for the film production and cinema exhibition industries, ensuring:

• Consistent High-Quality Multi-Channel Audio
  Standardized stripe locations guarantee compatibility between film prints and projector sound heads, enabling immersive six-track magnetic sound reproduction in theaters.

• Interoperability of Release Prints
  Uniform stripe dimensions and placement allow release prints to be used across different cinemas worldwide without sound degradation or synchronization issues.

• Accurate Cinematic Sound Synchronization
  By specifying picture-sound displacement and alignment, ISO 2404 helps prevent audio lag or desynchronization during projection, improving audience experience.

• Guidelines for Equipment Manufacturers
  Manufacturers of magnetic sound recording and playback equipment use this standard to design heads and systems compatible with 70 mm six-track striped prints.

• Reference for Special Effects Design
  Film producers and sound engineers can modify magnetic stripe arrangements within the standard’s framework to create distinct audio effects.

Related Standards

• ISO 3023: Cinematography - 65 mm and 70 mm unexposed motion-picture film - Cutting and perforating dimensions
  Specifies the physical characteristics of the base 70 mm film strip used alongside ISO 2404 magnetic sound specifications.

• Other ISO cinematography standards
  Standards addressing film formats, sound tracks, and projection technologies which complement the technical consistency initiated by ISO 2404.

Adhering to ISO 2404 ensures that six-track magnetic sound records on 70 mm release prints maintain the highest technical quality and compatibility, supporting the continued legacy of premium cinematic sound reproduction in the global film industry.