ISO 8590:1994

Overview

ISO 8590:1994 specifies the recorded characteristic for audio on 70 mm motion‑picture release prints that use magnetic stripes. The standard defines the recorded relative magnetic flux level (in dB) as a function of frequency (Hz) for playback at the nominal speed of 24 frames per second, with the reference level set to 0 dB at 1 000 Hz. It provides the characteristic curve, tabulated values and tolerances used to ensure consistent reproduction of multi‑track magnetic audio on 70 mm release prints.

Key topics and technical requirements

• Recorded characteristic definition: The standard expresses the relative magnetic flux level L* as a function of frequency and includes the mathematical formulation used to derive the characteristic.
• Reference and normalization: Levels are normalized so that Lo = 0 at 1 000 Hz (reference frequency).
• Time‑constant based shaping: The characteristic is obtained using two time constants specified in the document (numeric values shown in the standard) to describe pre‑emphasis/de‑emphasis behavior across frequency.
• Frequency vs dB table: Table 1 lists approximate recorded relative magnetic flux values from very low frequencies up to 16 kHz, together with tolerance bands for compliance testing.
• Notes on low‑frequency handling: The standard remarks that an infinite low‑frequency time constant provides better headroom but retains a finite low‑frequency pre‑emphasis value for compatibility with existing theatre equipment.

Applications and who uses it

ISO 8590:1994 is practical for professionals and organizations involved in analogue film sound production, distribution and playback:

• Film sound engineers specifying or evaluating magnetic stripe recordings on 70 mm prints.
• Post‑production facilities preparing release prints or aligning recording equipment to standardized characteristics.
• Film laboratories and duplication houses ensuring print-to-print consistency of magnetic audio levels and frequency response.
• Cinema equipment manufacturers and maintenance technicians calibrating playback heads and equalization to meet expected reproduction curves.
• Archives and restoration specialists checking original 70 mm magnetic tracks against the standard during preservation and transfer.

Related standards and context

• Prepared by ISO/TC 36 (Cinematography); this 1994 second edition supersedes the 1985 edition of the same reference.
• Use alongside other cinematography audio and film handling standards when designing end‑to‑end workflows for 70 mm magnetic audio reproduction.

Keywords: ISO 8590, 70 mm motion‑picture release prints, magnetic stripes, recorded characteristic, magnetic flux level, 24 frames per second, cinematography, audio standard.