Add American V8 preset, carb fuel transport, and adaptive desktop audio

include/FluidSim/AudioOutputStream.hpp

@@ -14,6 +14,8 @@ public:
     void set_speed(double speed) { speed_.store(speed, std::memory_order_relaxed); }
     std::uint64_t underrun_blocks() const { return underrun_blocks_.load(std::memory_order_relaxed); }
     double speed() const { return speed_.load(std::memory_order_relaxed); }
+    void set_auto_gain(bool enabled) { auto_gain_enabled_.store(enabled, std::memory_order_relaxed); }
+    bool auto_gain() const { return auto_gain_enabled_.load(std::memory_order_relaxed); }
 
 private:
     static constexpr std::size_t block_size = 512;
@@ -22,6 +24,9 @@ private:
     std::array<std::int16_t, block_size * 2> output_{};
     std::atomic<std::uint64_t> underrun_blocks_{};
     std::atomic<double> speed_{1.0};
+    std::atomic<bool> auto_gain_enabled_{true};
+    float rms_power_{}, peak_envelope_{}, automatic_gain_{1.f};
+    float level_alpha_{}, peak_decay_{}, gain_rise_alpha_{}, gain_fall_alpha_{};
     float previous_input_left_{}, previous_output_left_{};
     float previous_input_right_{}, previous_output_right_{};