[MSSL Research Log Vol.03] Psychoacoustic Hacking: The Relationship Between Headphone Output Levels and Spatial Audio Plugin Parameters

Overview: This log explores the critical relationship between systemic loudness and the psychoacoustic perception of spatial audio, specifically focusing on how output levels influence the brain's interpretation of "floor-plane" positioning.

Technical Findings (Fact): Our experiment (EXP-001) using dearVR PRO2 yielded these definitive results:

• Without Early Reflections: Even when Elevation is set to -84°, sound images collapse toward the horizontal plane.

• With 1.4m Floor Reflection: A robust and stable downward localization is achieved.

• 300Hz Low-pass Filter on Bottom Reflections: By removing high-frequency transients and isolating the low-mid "thud" of the heel, we successfully triggered the brain's "floor recognition switch."

System Calibration (Absolute Reference): To ensure repeatability, I have locked the following signal path parameters:

• DAW (Pro Tools) True Peak: -3.4 LKFS

• Momentary Loudness: -29.3 LKFS (17s average)

• Hardware (Sony MDR-CD900ST): OS output at approx. -20dB (50% physical volume).

Hypothesis: We believe that at these specific dynamic levels, the acoustic energy effectively breaches the threshold defined by the Fechner Law (equal-loudness contours), creating a "spatial reality" that standard mixing levels cannot replicate.