Acoustic Coherence and Cognitive Fatigue in Digital Audio: A MultiMethod Study of A4 = 432 Hz versus 440 Hz Using Sound Fission Protocols (FSE/FDT)

The international tuning standard A4 = 440 Hz (ISO 16:1975) has been questioned for potential differential effects on auditory cognitive fatigue, although systematic evidence remains limited. This study comparatively evaluates the acoustic stability and cognitive load of A4 = 432 Hz versus 440 Hz using controlled experimental protocols developed over 25 years of systematic research. A convergent multi-method design was employed, comprising: technical acoustic stability tests using the Sound Fission Protocol by Energy Saturation (FSE-v2.5) and the Fission by Temporal Desynchronization Protocol (FDT-v3.1); a double-blind counterbalanced crossover pilot study with human participants (n = 35) measuring cognitive fatigue via the validated Auditory Cognitive Fatigue Scale (EFCA); and predictive computational modeling. Technical analyses demonstrated that 432 Hz requires significantly more energy to induce distortion and exhibits greater tolerance to temporal desynchronization. The human study revealed a statistically significant reduction in self-reported cognitive fatigue following 432 Hz exposure. All effects survived Bonferroni correction. These findings provide the empirical foundation for the Acoustic Coherence Index (ICA), a signal-level metric currently being integrated into the IEEE P1857.16 audio coding standard — the first international standard to incorporate neurofysiological criteria in audio compression algorithm design.