commit 98cb5a4e4558754b748ee5cad0d351f960fd8514
parent 95b491117c96576a24150ef5463486f2368dd784
Author: Matt Demanett <matt@demanett.net>
Date: Sat, 21 Apr 2018 20:23:18 -0400
Implement fast/clean CIC decimator.
Diffstat:
11 files changed, 151 insertions(+), 35 deletions(-)
diff --git a/benchmarks/filter_benchmark.cpp b/benchmarks/filter_benchmark.cpp
@@ -7,19 +7,33 @@
using namespace bogaudio::dsp;
-static void BM_Decimator(benchmark::State& state) {
+static void BM_LPFDecimator(benchmark::State& state) {
WhiteNoiseGenerator r;
const int n = 8;
float buf[n];
for (int i = 0; i < n; ++i) {
buf[i] = r.next();
}
- Decimator d(44100.0, n);
+ LPFDecimator d(44100.0, n);
for (auto _ : state) {
- benchmark::DoNotOptimize(d.next(n, buf));
+ benchmark::DoNotOptimize(d.next(buf));
}
}
-BENCHMARK(BM_Decimator);
+BENCHMARK(BM_LPFDecimator);
+
+static void BM_CICDecimator(benchmark::State& state) {
+ WhiteNoiseGenerator r;
+ const int n = 8;
+ float buf[n];
+ for (int i = 0; i < n; ++i) {
+ buf[i] = r.next();
+ }
+ CICDecimator d(4, 8);
+ for (auto _ : state) {
+ benchmark::DoNotOptimize(d.next(buf));
+ }
+}
+BENCHMARK(BM_CICDecimator);
static void BM_RackDecimator(benchmark::State& state) {
WhiteNoiseGenerator r;
diff --git a/src/FMOp.cpp b/src/FMOp.cpp
@@ -116,7 +116,7 @@ void FMOp::step() {
_phasor.advancePhase();
_buffer[i] = _sineTable.nextFromPhasor(_phasor, Phasor::radiansToPhase(offset));
}
- float out = _decimator.next(oversample, _buffer);
+ float out = _decimator.next(_buffer);
out *= _level;
if (_levelEnvelopeOn) {
out *= envelope;
diff --git a/src/FMOp.hpp b/src/FMOp.hpp
@@ -65,7 +65,7 @@ struct FMOp : Module {
ADSR _envelope;
Phasor _phasor;
SineTableOscillator _sineTable;
- Decimator _decimator;
+ LPFDecimator _decimator;
SchmittTrigger _gateTrigger;
FMOp() : Module(NUM_PARAMS, NUM_INPUTS, NUM_OUTPUTS, NUM_LIGHTS) {
diff --git a/src/Test.cpp b/src/Test.cpp
@@ -235,10 +235,10 @@ void Test::step() {
squareBuf[i] = _square.nextFromPhasor(_oversampledPhasor);
}
- out += _sawDecimator.next(OVERSAMPLEN, sawBuf) * oMix;
+ out += _sawDecimator.next(sawBuf) * oMix;
// out += _sawRackDecimator.process(sawBuf) * oMix;
- out2 += _squareDecimator.next(OVERSAMPLEN, squareBuf) * oMix;
+ out2 += _squareDecimator.next(squareBuf) * oMix;
// out2 += _squareRackDecimator.process(squareBuf) * oMix;
}
else {
@@ -250,6 +250,24 @@ void Test::step() {
outputs[OUT_OUTPUT].value = out * 5.0f;
outputs[OUT2_OUTPUT].value = out2 * 5.0f;
+#elif DECIMATORS
+ const int quality = 12;
+ float sampleRate = engineGetSampleRate();
+ float frequency = oscillatorPitch(15000.0);
+ _saw.setSampleRate(sampleRate);
+ _saw.setFrequency(frequency / (float)OVERSAMPLEN);
+ _saw.setQuality(quality);
+ _cicDecimator.setParams(sampleRate, OVERSAMPLEN);
+ _lpfDecimator.setParams(sampleRate, OVERSAMPLEN);
+
+ float buf[OVERSAMPLEN] {};
+ for (int i = 0; i < OVERSAMPLEN; ++i) {
+ buf[i] = _saw.next();
+ }
+ outputs[OUT_OUTPUT].value = _cicDecimator.next(buf) * 5.0f;
+ // outputs[OUT2_OUTPUT].value = _lpfDecimator.next(buf) * 5.0f;
+ outputs[OUT2_OUTPUT].value = _rackDecimator.process(buf) * 5.0f;
+
#elif FM
const float amplitude = 5.0f;
float baseHz = oscillatorPitch();
diff --git a/src/Test.hpp b/src/Test.hpp
@@ -16,9 +16,10 @@ extern Model* modelTest;
// #define OVERSAMPLING 1
// #define OVERSAMPLED_BL 1
// #define ANTIALIASING 1
+#define DECIMATORS 1
// #define FM 1
// #define PM 1
-#define FEEDBACK_PM 1
+// #define FEEDBACK_PM 1
// #define EG 1
// #define TABLES 1
@@ -54,6 +55,10 @@ extern Model* modelTest;
#include "dsp/oscillator.hpp"
#include "dsp/decimator.hpp" // rack
#include "dsp/filter.hpp"
+#elif DECIMATORS
+#include "dsp/oscillator.hpp"
+#include "dsp/filter.hpp"
+#include "dsp/decimator.hpp" // rack
#elif FM
#include "dsp/oscillator.hpp"
#elif PM
@@ -105,7 +110,8 @@ struct Test : Module {
LowPassFilter _lpf;
#elif SINE
SineOscillator _sine;
- SineTableOscillator _sine2;
+ SineTable _table;
+ TablePhasor _sine2;
#elif SQUARE
SquareOscillator _square;
BandLimitedSquareOscillator _square2;
@@ -141,10 +147,17 @@ struct Test : Module {
Phasor _oversampledPhasor;
BandLimitedSawOscillator _saw;
BandLimitedSquareOscillator _square;
- bogaudio::dsp::Decimator _sawDecimator;
- bogaudio::dsp::Decimator _squareDecimator;
+ bogaudio::dsp::LPFDecimator _sawDecimator;
+ bogaudio::dsp::LPFDecimator _squareDecimator;
rack::Decimator<OVERSAMPLEN, OVERSAMPLEN> _sawRackDecimator;
rack::Decimator<OVERSAMPLEN, OVERSAMPLEN> _squareRackDecimator;
+#elif DECIMATORS
+ #define OVERSAMPLEN 8
+ #define STAGES 4
+ BandLimitedSawOscillator _saw;
+ bogaudio::dsp::CICDecimator _cicDecimator;
+ bogaudio::dsp::LPFDecimator _lpfDecimator;
+ rack::Decimator<OVERSAMPLEN, OVERSAMPLEN> _rackDecimator;
#elif FM
float _baseHz = 0.0f;
float _ratio = 0.0f;
@@ -169,13 +182,19 @@ struct Test : Module {
Test()
: Module(NUM_PARAMS, NUM_INPUTS, NUM_OUTPUTS, NUM_LIGHTS)
-#if TABLES
+#if SINE
+ , _table(12)
+ , _sine2(_table)
+#elif DECIMATORS
+ , _cicDecimator(STAGES)
+#elif TABLES
, _table(StaticBlepTable::table(), 44100.0, 1000.0)
#endif
{
onReset();
#ifdef SINE
+ _table.generate();
_sine2.setPhase(M_PI);
#elif SAW
diff --git a/src/VCO.cpp b/src/VCO.cpp
@@ -102,13 +102,13 @@ void VCO::step() {
}
}
if (outputs[SQUARE_OUTPUT].active) {
- squareOut += oMix * amplitude * _squareDecimator.next(oversample, _squareBuffer);
+ squareOut += oMix * amplitude * _squareDecimator.next(_squareBuffer);
}
if (outputs[SAW_OUTPUT].active) {
- sawOut += oMix * amplitude * _sawDecimator.next(oversample, _sawBuffer);
+ sawOut += oMix * amplitude * _sawDecimator.next(_sawBuffer);
}
if (outputs[TRIANGLE_OUTPUT].active) {
- triangleOut += oMix * amplitude * _triangleDecimator.next(oversample, _triangleBuffer);
+ triangleOut += oMix * amplitude * _triangleDecimator.next(_triangleBuffer);
}
}
else {
diff --git a/src/VCO.hpp b/src/VCO.hpp
@@ -61,9 +61,9 @@ struct VCO : Module {
BandLimitedSawOscillator _saw;
TriangleOscillator _triangle;
SineTableOscillator _sine;
- Decimator _squareDecimator;
- Decimator _sawDecimator;
- Decimator _triangleDecimator;
+ CICDecimator _squareDecimator;
+ CICDecimator _sawDecimator;
+ CICDecimator _triangleDecimator;
float _squareBuffer[oversample];
float _sawBuffer[oversample];
float _triangleBuffer[oversample];
diff --git a/src/XCO.cpp b/src/XCO.cpp
@@ -153,19 +153,19 @@ void XCO::step() {
}
}
if (squareOversample) {
- squareOut += oMix * amplitude * _squareDecimator.next(oversample, _squareBuffer);
+ squareOut += oMix * amplitude * _squareDecimator.next(_squareBuffer);
}
if (sawOversample) {
- sawOut += oMix * amplitude * _sawDecimator.next(oversample, _sawBuffer);
+ sawOut += oMix * amplitude * _sawDecimator.next(_sawBuffer);
}
if (triangleOversample) {
- triangleOut += amplitude * _triangleDecimator.next(oversample, _triangleBuffer);
+ triangleOut += amplitude * _triangleDecimator.next(_triangleBuffer);
if (!triangleSample) {
triangleOut *= oMix;
}
}
if (sineOversample) {
- sineOut += amplitude * _sineDecimator.next(oversample, _sineBuffer);
+ sineOut += amplitude * _sineDecimator.next(_sineBuffer);
}
}
else {
diff --git a/src/XCO.hpp b/src/XCO.hpp
@@ -96,10 +96,10 @@ struct XCO : Module {
BandLimitedSawOscillator _saw;
TriangleOscillator _triangle;
SineTableOscillator _sine;
- Decimator _squareDecimator;
- Decimator _sawDecimator;
- Decimator _triangleDecimator;
- Decimator _sineDecimator;
+ CICDecimator _squareDecimator;
+ CICDecimator _sawDecimator;
+ CICDecimator _triangleDecimator;
+ CICDecimator _sineDecimator;
float _squareBuffer[oversample];
float _sawBuffer[oversample];
float _triangleBuffer[oversample];
diff --git a/src/dsp/filter.cpp b/src/dsp/filter.cpp
@@ -177,20 +177,60 @@ float MultipoleFilter::next(float sample) {
}
-void Decimator::setParams(float sampleRate, int oversample) {
+void LPFDecimator::setParams(float sampleRate, int factor) {
+ _factor = factor;
_filter.setParams(
MultipoleFilter::LP_TYPE,
4,
- oversample * sampleRate,
+ factor * sampleRate,
0.45f * sampleRate,
0
);
}
-float Decimator::next(int n, const float* buf) {
+float LPFDecimator::next(const float* buf) {
float s = 0.0f;
- for (int i = 0; i < n; ++i) {
+ for (int i = 0; i < _factor; ++i) {
s = _filter.next(buf[i]);
}
return s;
}
+
+
+// cascaded integrator–comb decimator: https://en.wikipedia.org/wiki/Cascaded_integrator%E2%80%93comb_filter
+CICDecimator::CICDecimator(int stages, int factor) {
+ assert(stages > 0);
+ _stages = stages;
+ _integrators = new T[_stages + 1] {};
+ _combs = new T[_stages] {};
+ setParams(0.0f, factor);
+}
+
+CICDecimator::~CICDecimator() {
+ delete[] _integrators;
+ delete[] _combs;
+}
+
+void CICDecimator::setParams(float _sampleRate, int factor) {
+ assert(factor > 0);
+ if (_factor != factor) {
+ _factor = factor;
+ _gainCorrection = 1.0f / (float)(pow(_factor, _stages));
+ }
+}
+
+float CICDecimator::next(const float* buf) {
+ for (int i = 0; i < _factor; ++i) {
+ _integrators[0] = buf[i] * scale;
+ for (int j = 1; j <= _stages; ++j) {
+ _integrators[j] += _integrators[j - 1];
+ }
+ }
+ T s = _integrators[_stages];
+ for (int i = 0; i < _stages; ++i) {
+ T t = s;
+ s -= _combs[i];
+ _combs[i] = t;
+ }
+ return _gainCorrection * (s / (float)scale);
+}
diff --git a/src/dsp/filter.hpp b/src/dsp/filter.hpp
@@ -1,5 +1,6 @@
#pragma once
+#include <stdint.h>
#include <math.h>
#include "buffer.hpp"
@@ -127,14 +128,38 @@ struct MultipoleFilter : Filter {
};
struct Decimator {
+ Decimator() {}
+ virtual ~Decimator() {}
+
+ virtual void setParams(float sampleRate, int factor) = 0;
+ virtual float next(const float* buf) = 0;
+};
+
+struct LPFDecimator : Decimator {
+ int _factor;
MultipoleFilter _filter;
- Decimator(float sampleRate = 1000.0f, int oversample = 4) {
- setParams(sampleRate, oversample);
+ LPFDecimator(float sampleRate = 1000.0f, int factor = 8) {
+ setParams(sampleRate, factor);
}
+ virtual void setParams(float sampleRate, int factor) override;
+ virtual float next(const float* buf) override;
+};
+
+struct CICDecimator : Decimator {
+ typedef int64_t T;
+ static constexpr T scale = 1l << 32;
+ int _stages;
+ T* _integrators;
+ T* _combs;
+ int _factor = 0;
+ float _gainCorrection;
+
+ CICDecimator(int stages = 4, int factor = 8);
+ virtual ~CICDecimator();
- void setParams(float sampleRate, int oversample);
- float next(int n, const float* buf);
+ virtual void setParams(float sampleRate, int factor) override;
+ virtual float next(const float* buf) override;
};
} // namespace dsp
