Overview
ISO 6025:2000 - Cinematography - Analogue photographic sound test films, 35 mm and 16 mm - Specifications - defines the technical characteristics and test types for analogue photographic sound test films used to check, adjust and measure motion‑picture projector sound systems and sound‑reproducing channels. The standard covers both 35 mm and 16 mm formats and supports monophonic and stereophonic reproduction, providing consistent test signals and dimensional references for international exchange of test films.
Key topics and technical requirements
- Test film types: Films for focus/azimuth, lateral position (buzz track), scanning‑beam uniformity (snake track), level/output balance (variable‑area modulation), frequency response and film‑velocity non‑uniformity (flutter).
- Format specifics: Uses standard 35 mm and 16 mm cutting/perforation and track dimensions (conforming to referenced ISO film dimension standards). Polyester or low‑shrinkage triacetate bases are preferred.
- Representative signal parameters:
- Focus/azimuth tones: 9 kHz (35 mm) and 7.1 kHz (16 mm) with tight tolerances and long duration (100 s).
- Buzz track: square waves at 300 Hz (picture side) and 1 000 Hz (opposite side).
- Snake track: 1 000 Hz sweep for illumination uniformity.
- Level test (variable area): 1 000 Hz (35 mm) and 400 Hz (16 mm) with photoelectric output factor (POF) guidance (example POF ≈ 0.344 for a nominal 50% 35 mm stereophonic track).
- Frequency response: multi‑frequency series (from tens of Hz to >10 kHz) with defined tolerances and durations.
- Flutter: 3 150 Hz test tone and wow/flutter limits measured per IEC 60386.
- Quality controls: Splice restrictions, azimuth tolerance guidance (informative annex recommends tighter than ±5’ and ideally within ±2’ of arc), modulation and distortion limits, and duration requirements.
Applications
ISO 6025 test films are practical tools for:
- Commissioning and routine maintenance of cinema projector sound systems
- Calibration of film scanners, optical sound reproducers and audio playback chains
- Measuring frequency response, channel balance, scanning‑beam alignment and flutter/wow
- Film laboratories and post‑production quality control, archival playback verification, and equipment manufacturers for product testing
Who uses this standard
- Projectionists and theatre engineers
- Audio/visual installers and service technicians
- Film laboratory technicians and restoration specialists
- Equipment manufacturers and quality engineers
- Standards bodies and test labs working on analogue optical sound systems
Related standards
Key normative references include ISO 491 (35 mm), ISO 69 (16 mm), ISO 7343, ISO 4243, IEC 60386, and related documents such as ISO 7739 and ISO 7832 for track dimensions and photoelectric output factor measurement.
Keywords: ISO 6025, cinematography standard, analogue photographic sound test films, 35 mm, 16 mm, azimuth, buzz track, snake track, photoelectric output factor (POF), frequency response, flutter.