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Warmth Servo

Look up syntax, contracts, layouts, algorithms, and exact behavior.

The Warmth Servo is Hearth's main product-level differentiator. It watches inexpensive proxies for level, brightness, roughness, and transient density, then applies conservative corrections to the nonlinear core. When brightness or roughness rise, upper-band drive and post-emphasis back off. When the source is dull but peaky, bloom and mild bias can increase. When a bus is already dense, the device leans on flux behavior instead of extra high-band tube drive.

low brightnesshigh brightnessdriveservo thresholdupper-band drive backs off
Upper-band drive response. The servo leaves safe sources mostly unchanged and increasingly attenuates upper-band drive as brightness rises.
B[n]=Ehigh[n]Elow[n]+Emid[n]+ϵB[n] = \frac{E_{\mathrm{high}}[n]}{E_{\mathrm{low}}[n] + E_{\mathrm{mid}}[n] + \epsilon}
Brightness proxy. A high-band energy ratio acts as a cheap proxy for spectral centroid and perceived brightness.

The servo is intentionally slow and bounded. It should feel like good gain staging and tone placement, not like an obvious modulation effect.

This is a guard-rail system rather than an automatic mastering processor. It does not try to decide what the user should like. It lowers the probability that turning up warmth also turns up glare, brittle roughness, or uncontrolled high-band drive.

Gupper[n]=1−A⋅σ(B[n]−B0)−R⋅σ(ρ[n]−ρ0)G_{\mathrm{upper}}[n] = 1 - A \cdot \sigma(B[n] - B_0) - R \cdot \sigma(\rho[n] - \rho_0)
Servo gain. Upper-band drive is reduced when brightness or roughness exceed their comfort thresholds.

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