dc removal and safety saturation and more

plugins/GranularPitchShifter/GranularPitchShifterEffect.cpp

@@ -80,7 +80,7 @@ bool GranularPitchShifterEffect::processAudioBuffer(sampleFrame* buf, const fpp_
 	const float glide = m_granularpitchshifterControls.m_glideModel.value();
 	const int minLatency = m_granularpitchshifterControls.m_minLatencyModel.value() * m_sampleRate;
 	const float densityInvRoot = std::sqrt(1.f / density);
-	const float feedback = m_granularpitchshifterControls.m_feedbackModel.value() * densityInvRoot;
+	const float feedback = m_granularpitchshifterControls.m_feedbackModel.value();
 	const float fadeLength = 1.f / m_granularpitchshifterControls.m_fadeLengthModel.value();
 	const bool prefilter = m_granularpitchshifterControls.m_prefilterModel.value();
 
@@ -201,7 +201,7 @@ bool GranularPitchShifterEffect::processAudioBuffer(sampleFrame* buf, const fpp_
 			if (m_grains[i].readPoint[0] >= m_ringBufLength) { m_grains[i].readPoint[0] -= m_ringBufLength; }
 			if (m_grains[i].readPoint[1] >= m_ringBufLength) { m_grains[i].readPoint[1] -= m_ringBufLength; }
 
-			const float fadePos = std::clamp((-std::fabs(-2.f * static_cast<float>(m_grains[i].phase) + 1.f) + 0.5f) * fadeLength + 0.5f, 0.f, 1.f);
+			const float fadePos = std::clamp((-std::abs(-2.f * static_cast<float>(m_grains[i].phase) + 1.f) + 0.5f) * fadeLength + 0.5f, 0.f, 1.f);
 			const float windowVal = cosHalfWindowApprox(fadePos, shapeK);
 			s[0] += getHermiteSample(m_grains[i].readPoint[0], 0) * windowVal;
 			s[1] += getHermiteSample(m_grains[i].readPoint[1], 1) * windowVal;
@@ -211,6 +211,17 @@ bool GranularPitchShifterEffect::processAudioBuffer(sampleFrame* buf, const fpp_
 		s[0] *= densityInvRoot;
 		s[1] *= densityInvRoot;
 
+		// 1-pole highpass for DC offset removal, to make feedback safer
+		s[0] -= (m_dcVal[0] = (1.f - m_dcCoeff) * s[0] + m_dcCoeff * m_dcVal[0]);
+		s[1] -= (m_dcVal[1] = (1.f - m_dcCoeff) * s[1] + m_dcCoeff * m_dcVal[1]);
+
+		// cheap safety saturator to protect against infinite feedback
+		if (feedback > 0)
+		{
+			s[0] = safetySaturate(s[0]);
+			s[1] = safetySaturate(s[1]);
+		}
+
 		if (++m_writePoint >= m_ringBufLength)
 		{
 			m_writePoint = 0;
@@ -261,6 +272,8 @@ void GranularPitchShifterEffect::changeSampleRate()
 	m_grains.clear();
 	m_grainCount = 0;
 	m_grains.reserve(8);// arbitrary
+
+	m_dcCoeff = std::exp(-2.0 * M_PI * DcRemovalHz / m_sampleRate);
 }
 
 

plugins/GranularPitchShifter/GranularPitchShifterEffect.h

@@ -38,6 +38,7 @@ constexpr float PrefilterBandwidth = 0.96f;// 96% of nyquist
 constexpr double GlideSnagRadius = 0.001;
 constexpr int SafetyLatency = 3;
 constexpr float RangeSeconds[5] = {5, 10, 40, 40, 120};
+constexpr float DcRemovalHz = 7;
 
 
 class GranularPitchShifterEffect : public Effect
@@ -94,6 +95,13 @@ class GranularPitchShifterEffect : public Effect
 		return -6.0026608f + p * (6.8773512f - 1.5838104f * p);
 	}
 
+	// designed to use minimal CPU if the input isn't loud
+	float safetySaturate(float input)
+	{
+		float absInput = std::abs(input);
+		return absInput <= 16 ? input : std::copysign((absInput - 16) / (1 + (absInput - 16) * 0.001f) + 16, input);
+	}
+
 	void sampleRateNeedsUpdate() { m_sampleRateNeedsUpdate = true; }
 
 	void changeSampleRate();
@@ -147,10 +155,12 @@ class GranularPitchShifterEffect : public Effect
 	std::array<PrefilterLowpass, 2> m_prefilter;
 	std::array<double, 2> m_speed = {1, 1};
 	std::array<double, 2> m_truePitch = {0, 0};
+	std::array<float, 2> m_dcVal = {0, 0};
 
 	float m_sampleRate;
 	float m_nyquist;
 	float m_nextWaitRandomization = 1;
+	float m_dcCoeff;
 
 	int m_ringBufLength = 0;
 	int m_writePoint = 0;