Rack/plugins/community/repos/Fundamental/src/VCF.cpp

#include "Fundamental.hpp"
#include "dsp/functions.hpp"
#include "dsp/resampler.hpp"
#include "dsp/ode.hpp"


inline float clip(float x) {
	return tanhf(x);
}

struct LadderFilter {
	float omega0;
	float resonance = 1.0f;
	float state[4];
	float input;
	float lowpass;
	float highpass;

	LadderFilter() {
		reset();
		setCutoff(0.f);
	}

	void reset() {
		for (int i = 0; i < 4; i++) {
			state[i] = 0.f;
		}
	}

	void setCutoff(float cutoff) {
		omega0 = 2.f*M_PI * cutoff;
	}

	void process(float input, float dt) {
		ode::stepRK4(0.f, dt, state, 4, [&](float t, const float x[], float dxdt[]) {
			float inputc = clip(input - resonance * x[3]);
			float yc0 = clip(x[0]);
			float yc1 = clip(x[1]);
			float yc2 = clip(x[2]);
			float yc3 = clip(x[3]);

			dxdt[0] = omega0 * (inputc - yc0);
			dxdt[1] = omega0 * (yc0 - yc1);
			dxdt[2] = omega0 * (yc1 - yc2);
			dxdt[3] = omega0 * (yc2 - yc3);
		});

		lowpass = state[3];
		// TODO This is incorrect when `resonance > 0`. Is the math wrong?
		highpass = clip((input - resonance*state[3]) - 4 * state[0] + 6*state[1] - 4*state[2] + state[3]);
	}
};


static const int UPSAMPLE = 2;

struct VCF : Module {
	enum ParamIds {
		FREQ_PARAM,
		FINE_PARAM,
		RES_PARAM,
		FREQ_CV_PARAM,
		DRIVE_PARAM,
		NUM_PARAMS
	};
	enum InputIds {
		FREQ_INPUT,
		RES_INPUT,
		DRIVE_INPUT,
		IN_INPUT,
		NUM_INPUTS
	};
	enum OutputIds {
		LPF_OUTPUT,
		HPF_OUTPUT,
		NUM_OUTPUTS
	};

	LadderFilter filter;
	// Upsampler<UPSAMPLE, 8> inputUpsampler;
	// Decimator<UPSAMPLE, 8> lowpassDecimator;
	// Decimator<UPSAMPLE, 8> highpassDecimator;

	VCF() : Module(NUM_PARAMS, NUM_INPUTS, NUM_OUTPUTS) {}

	void onReset() override {
		filter.reset();
	}

	void step() override {
		if (!outputs[LPF_OUTPUT].active && !outputs[HPF_OUTPUT].active) {
			outputs[LPF_OUTPUT].value = 0.f;
			outputs[HPF_OUTPUT].value = 0.f;
			return;
		}

		float input = inputs[IN_INPUT].value / 5.f;
		float drive = clamp(params[DRIVE_PARAM].value + inputs[DRIVE_INPUT].value / 10.f, 0.f, 1.f);
		float gain = powf(1.f + drive, 5);
		input *= gain;

		// Add -60dB noise to bootstrap self-oscillation
		input += 1e-6f * (2.f * randomUniform() - 1.f);

		// Set resonance
		float res = clamp(params[RES_PARAM].value + inputs[RES_INPUT].value / 10.f, 0.f, 1.f);
		filter.resonance = powf(res, 2) * 10.f;

		// Set cutoff frequency
		float pitch = 0.f;
		if (inputs[FREQ_INPUT].active)
			pitch += inputs[FREQ_INPUT].value * quadraticBipolar(params[FREQ_CV_PARAM].value);
		pitch += params[FREQ_PARAM].value * 10.f - 5.f;
		pitch += quadraticBipolar(params[FINE_PARAM].value * 2.f - 1.f) * 7.f / 12.f;
		float cutoff = 261.626f * powf(2.f, pitch);
		cutoff = clamp(cutoff, 1.f, 8000.f);
		filter.setCutoff(cutoff);

		/*
		// Process sample
		float dt = engineGetSampleTime() / UPSAMPLE;
		float inputBuf[UPSAMPLE];
		float lowpassBuf[UPSAMPLE];
		float highpassBuf[UPSAMPLE];
		inputUpsampler.process(input, inputBuf);
		for (int i = 0; i < UPSAMPLE; i++) {
			// Step the filter
			filter.process(inputBuf[i], dt);
			lowpassBuf[i] = filter.lowpass;
			highpassBuf[i] = filter.highpass;
		}

		// Set outputs
		if (outputs[LPF_OUTPUT].active) {
			outputs[LPF_OUTPUT].value = 5.f * lowpassDecimator.process(lowpassBuf);
		}
		if (outputs[HPF_OUTPUT].active) {
			outputs[HPF_OUTPUT].value = 5.f * highpassDecimator.process(highpassBuf);
		}
		*/
		filter.process(input, engineGetSampleTime());
		outputs[LPF_OUTPUT].value = 5.f * filter.lowpass;
		outputs[HPF_OUTPUT].value = 5.f * filter.highpass;
	}
};


struct VCFWidget : ModuleWidget {
	VCFWidget(VCF *module) : ModuleWidget(module) {
		setPanel(SVG::load(assetPlugin(plugin, "res/VCF.svg")));

		addChild(Widget::create<ScrewSilver>(Vec(15, 0)));
		addChild(Widget::create<ScrewSilver>(Vec(box.size.x - 30, 0)));
		addChild(Widget::create<ScrewSilver>(Vec(15, 365)));
		addChild(Widget::create<ScrewSilver>(Vec(box.size.x - 30, 365)));

		addParam(ParamWidget::create<RoundHugeBlackKnob>(Vec(33, 61), module, VCF::FREQ_PARAM, 0.f, 1.f, 0.5f));
		addParam(ParamWidget::create<RoundLargeBlackKnob>(Vec(12, 143), module, VCF::FINE_PARAM, 0.f, 1.f, 0.5f));
		addParam(ParamWidget::create<RoundLargeBlackKnob>(Vec(71, 143), module, VCF::RES_PARAM, 0.f, 1.f, 0.f));
		addParam(ParamWidget::create<RoundLargeBlackKnob>(Vec(12, 208), module, VCF::FREQ_CV_PARAM, -1.f, 1.f, 0.f));
		addParam(ParamWidget::create<RoundLargeBlackKnob>(Vec(71, 208), module, VCF::DRIVE_PARAM, 0.f, 1.f, 0.f));

		addInput(Port::create<PJ301MPort>(Vec(10, 276), Port::INPUT, module, VCF::FREQ_INPUT));
		addInput(Port::create<PJ301MPort>(Vec(48, 276), Port::INPUT, module, VCF::RES_INPUT));
		addInput(Port::create<PJ301MPort>(Vec(85, 276), Port::INPUT, module, VCF::DRIVE_INPUT));
		addInput(Port::create<PJ301MPort>(Vec(10, 320), Port::INPUT, module, VCF::IN_INPUT));

		addOutput(Port::create<PJ301MPort>(Vec(48, 320), Port::OUTPUT, module, VCF::LPF_OUTPUT));
		addOutput(Port::create<PJ301MPort>(Vec(85, 320), Port::OUTPUT, module, VCF::HPF_OUTPUT));
	}
};


RACK_PLUGIN_MODEL_INIT(Fundamental, VCF) {
   Model *modelVCF = Model::create<VCF, VCFWidget>("Fundamental", "VCF", "VCF", FILTER_TAG);
   return modelVCF;
}