Line data    Source code

       1              : #pragma once
       2              : 
       3              : // Preamp and tone-stack models for classic guitar amplifier voicings.
       4              : // Signal model: y = L * sat(G * H_tone{x}, mix, asymmetry), where H_tone is
       5              : // a low-shelf + peaking-mid + high-shelf biquad cascade. The factory models
       6              : // cover Clean American / Fender Twin, British Crunch / Marshall JCM800,
       7              : // High Gain Modern / Mesa Rectifier, and Jazz Warm / Roland JC-120. Dynamic
       8              : // sag follows an envelope e[n] = a*x_abs[n] + (1-a)*e[n-1] and reduces gain
       9              : // as the simulated supply is loaded.
      10              : 
      11              : #include "audio/effects/effect.h"
      12              : #include "audio/dsp/biquad.h"
      13              : 
      14              : namespace Amplitron {
      15              : 
      16              : /**
      17              :  * @brief Describes the tonal character of an amp model.
      18              :  *
      19              :  * Each model packages a characteristic tone-stack EQ curve, saturation
      20              :  * transfer function, and dynamic response into a single struct that the
      21              :  * AmpSimulator effect consumes.
      22              :  */
      23              : struct AmpModel {
      24              :     const char* name;          ///< Display name (e.g. "Clean American")
      25              :     const char* inspiration;   ///< Real-world amp inspiration
      26              :     const char* description;   ///< Short tonal description
      27              : 
      28              :     // --- Tone stack (3-band biquad EQ) ---
      29              :     float bass_freq;           ///< Low shelf center frequency (Hz)
      30              :     float bass_gain_db;        ///< Low shelf gain (dB)
      31              :     float bass_q;              ///< Low shelf Q factor
      32              :     float mid_freq;            ///< Mid peak center frequency (Hz)
      33              :     float mid_gain_db;         ///< Mid peak gain (dB)
      34              :     float mid_q;               ///< Mid peak Q factor
      35              :     float treble_freq;         ///< High shelf center frequency (Hz)
      36              :     float treble_gain_db;      ///< High shelf gain (dB)
      37              :     float treble_q;            ///< High shelf Q factor
      38              : 
      39              :     // --- Saturation ---
      40              :     float preamp_gain;         ///< Pre-saturation drive multiplier
      41              :     float saturation_mix;      ///< Blend of soft vs hard clipping [0=soft, 1=hard]
      42              :     float asymmetry;           ///< Positive-negative clipping ratio (1.0 = symmetric)
      43              :     float output_level;        ///< Post-saturation output scaling
      44              : 
      45              :     // --- Dynamic response ---
      46              :     float attack_coeff;        ///< Envelope follower attack speed (0-1, higher = faster)
      47              :     float release_coeff;       ///< Envelope follower release speed (0-1, higher = faster)
      48              :     float sag_amount;          ///< Power-sag simulation depth (0 = none)
      49              : };
      50              : 
      51              : /**
      52              :  * @brief Returns the built-in amp model library.
      53              :  * @return Vector of AmpModel structs for all factory amp types.
      54              :  */
      55              : const std::vector<AmpModel>& get_amp_models();
      56              : 
      57              : /**
      58              :  * @brief Preamp simulator effect with selectable amp models.
      59              :  *
      60              :  * Implements a complete preamp stage: input gain -> envelope follower ->
      61              :  * tone-stack EQ (3 biquad filters) -> waveshaping saturation -> output level.
      62              :  * The tonal character is defined by the selected AmpModel.
      63              :  */
      64            7 : class AmpSimulator : public Effect {
      65              : public:
      66              :     AmpSimulator();
      67              :     void process(float* buffer, int num_samples) override;
      68              :     void set_sample_rate(int sample_rate) override;
      69              :     void reset() override;
      70          341 :     const char* name() const override { return "Amp Sim"; }
      71            3 :     const char* type_id() const override { return "Amp Sim"; }
      72          144 :     std::vector<EffectParam>& params() override { return params_; }
      73              : 
      74              : private:
      75              :     std::vector<EffectParam> params_;
      76              : 
      77              :     // 3-band tone-stack biquad filters
      78              :     Biquad low_shelf_;
      79              :     Biquad mid_peak_;
      80              :     Biquad high_shelf_;
      81              : 
      82              :     // Envelope follower for dynamic response
      83              :     float envelope_ = 0.0f;
      84              : 
      85              :     // DC blocking high-pass state
      86              :     OnePole dc_block_;
      87              : 
      88              :     // One-pole smoothing states for trim parameters (avoids coefficient click on UI change)
      89              :     float bass_trim_state_ = 0.0f;
      90              :     float mid_trim_state_ = 0.0f;
      91              :     float treble_trim_state_ = 0.0f;
      92              :     float gain_smoothed_ = 0.5f;
      93              :     float level_smoothed_ = 0.7f;
      94              : 
      95              :     // Cached model index for dirty-check coefficient recomputation
      96              :     int cached_model_index_ = -1;
      97              :     float cached_bass_ = -999.0f;
      98              :     float cached_mid_ = -999.0f;
      99              :     float cached_treble_ = -999.0f;
     100              :     float cached_gain_ = -999.0f;
     101              : 
     102              :     void recompute_coefficients_if_dirty();
     103              : };
     104              : 
     105              : } // namespace Amplitron