Q-Attenuation & Occlusion

The attenuation system offers four propagation models: Natural, Linear, Inverse, and Logarithmic.

Natural and Inverse modes are derived from the inverse-square law of sound intensity, following a 6 dB SPL reduction per distance doubling. Linear provides a simplified fade for stylized use, while Logarithmic applies psychoacoustic compression for smooth near-field behavior.

The Air Absorption module reproduces high-frequency damping caused by air molecules. It applies approximately −0.3 dB of HF loss per meter and shifts the high-shelf cutoff from around 12 kHz at 0 m to 3 kHz at 50 m, generating realistic spatial depth and atmospheric coloration.

Occlusion is modeled as a frequency-dependent attenuation curve combining low-pass filtering, high-frequency loss, and broadband energy reduction. The effective occlusion factor is defined as:

Effective Occlusion = Occlusion × (1 − Open Gap)


This allows partial transmission through small openings such as windows or door gaps, maintaining smooth transitions between open and blocked states.

Each material profile defines its own low-pass cutoff target and high-frequency loss characteristics:

• Curtain: ≈1700 Hz base cutoff, −9 dB HF loss — porous and highly absorbent.

• Wood: ≈1300 Hz base cutoff, −7 dB HF loss — reflective with moderate damping.

• Concrete: ≈650 Hz base cutoff, −4 dB HF loss — dense and broadband reflective.

• Glass: ≈2200 Hz base cutoff, −8 dB HF loss — bright and thin, HF energy loss with limited broadband attenuation.

Broadband attenuation ranges from −6 dB to −12 dB depending on material type, replicating the perceived energy loss behind barriers. All filter coefficients are updated in real time, ensuring seamless response to parameter automation or dynamic control.

Mathematically, Q is grounded in classical acoustic propagation laws:

• Inverse-Square Law: SPL decreases proportionally to 1/r² with distance.

• Air Absorption: Frequency-dependent exponential HF loss modeled as linear per-meter decay.

• Material Filtering: Absorption coefficients translated into cutoff and gain parameters for IIR filters.

The processor runs in 32-bit floating-point precision and supports sample rates up to 192 kHz. It operates with zero latency and minimal CPU load, making it suitable for both runtime and offline production environments.

Parameter Summary:
Distance (0–50 m) controls overall level and attenuation curve.
Occlusion (0–100%) determines filtering intensity.
Open Gap (0–100%) reduces occlusion proportionally.
Material selects one of four acoustic surface profiles.
Air Absorption toggles atmospheric filtering.
Attenuation Mode selects propagation law.
Output Gain (−24 to +24 dB) compensates post-attenuation loss.
Bypass disables processing for A/B comparison.

System Requirements:
macOS 10.13 or later (AU, VST3, AAX, Unity).
Windows 10 or later (VST3, AAX).
Unity 2021 LTS or newer (drop-in native audio plugin).