bit_crusher.hpp

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// sbl/dsp/comp/bit_crusher.hpp — Bit depth reduction composition
//
// Reduces effective bit depth of audio signal.
// Wraps BitReducer primitive with a _su port for normalized input.
// Depth is deliberately unsmoothed (see set_depth_su).
//
// Signal Unit API (FDP-052):
//   set_depth_su(float) — [0,1] port. 0.0 = full resolution (16-bit, bypass),
//   1.0 = minimum resolution (~2 bits). Widget owns mapping and smoothing.
//
// Early-out: when depth is 0.0, processing is skipped entirely —
// no quantization noise when the effect is off.
//
// Usage:
//   sbl::dsp::comp::BitCrusher bc;
//   bc.set_depth_su(0.4f);          // moderate reduction
//   bc.process(buf, frames);
 
#ifndef SBL_DSP_COMP_BIT_CRUSHER_HPP_
#define SBL_DSP_COMP_BIT_CRUSHER_HPP_
 
#include <cstdint>
 
#include <sbl/dsp/primitives/bit_reducer.hpp>
#include <sbl/dsp/types/fixed.hpp>
 
namespace sbl::dsp::comp {
 
class BitCrusher {
public:
    static constexpr float kMaxBits = 16.0f;
    static constexpr float kMinBits = 2.0f;
 
    /// Port: set bit reduction depth [0, 1].
    /// 0.0 = full resolution (bypass), 1.0 = minimum bits.
    /// No smoothing — quantization grid changes must be instant.
    /// Smoothing a quantizer creates inter-grid artifacts (crackling).
    /// The pot deadband + cam table interpolation provide sufficient continuity.
    void set_depth_su(float su) { depth_su_ = su; }
 
    /// Process a block of samples in-place.
    /// Depth is constant across the block.
    void process(float* buf, uint16_t n) {
        if (depth_su_ < 1e-5f) return;
 
        float bits = kMaxBits - depth_su_ * (kMaxBits - kMinBits);
        reducer_.set_bits(bits);
        reducer_.process(buf, n);
    }
 
    void reset() { depth_su_ = 0.0f; }
 
private:
    primitives::BitReducer reducer_;
    float depth_su_ = 0.0f;
};
 
} // namespace sbl::dsp::comp
 
#endif // SBL_DSP_COMP_BIT_CRUSHER_HPP_