soft_limiter.hpp

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// sbl/dsp/soft_limiter.hpp — Soft limiter primitive
//
// Bounded rational sigmoid: x * (27 + x²) / (27 + 9x²)
// Same [3,2] Padé approximant as fast_tanhf, without clamping or NaN guard.
//
// Monotonic, odd-symmetric, unity gain at origin. NOT bounded — approaches
// x/9 for large x. For bounded [-1,1] output, clamp input to [-3,3] first.
//
// Key values: process(1.0) ≈ 0.78, process(3.0) = 1.0
//
// Usage:
//   sbl::dsp::SoftLimiter limiter;
//   float out = limiter.process(signal);
 
#ifndef SBL_DSP_PRIMITIVES_SOFT_LIMITER_HPP_
#define SBL_DSP_PRIMITIVES_SOFT_LIMITER_HPP_
 
#include <cstdint>
 
namespace sbl::dsp::primitives {
 
class SoftLimiter {
public:
    /// Process a single sample
    float process(float x) { return limit(x); }
 
    /// Process a block in-place
    void process(float* buf, uint16_t frames) {
        for (uint16_t i = 0; i < frames; ++i) {
            buf[i] = limit(buf[i]);
        }
    }
 
    /// The rational sigmoid, available for composition use
    static float limit(float x) {
        float x2 = x * x;
        return x * (27.0f + x2) / (27.0f + 9.0f * x2);
    }
};
 
} // namespace sbl::dsp::primitives
 
#endif // SBL_DSP_PRIMITIVES_SOFT_LIMITER_HPP_