diff --git a/.gitignore b/.gitignore
index b7539ce9..3c66e5f9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 build
 build-arm
 build-subl
-.vscode
\ No newline at end of file
+.vscode
+perf.data
+perf.data.old
\ No newline at end of file
diff --git a/.gitmodules b/.gitmodules
index 4ee0bf4e..b52b5486 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -16,3 +16,9 @@
 [submodule "external/readerwriterqueue"]
 	path = external/readerwriterqueue
 	url = https://github.com/cameron314/readerwriterqueue.git
+[submodule "external/gsl-lite"]
+	path = external/gsl-lite
+	url = https://github.com/martinmoene/gsl-lite.git
+[submodule "external/cnpy"]
+	path = external/cnpy
+	url = https://github.com/rogersce/cnpy.git
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f8edc1f2..eeb23cba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -17,7 +17,6 @@ if (UNIX)
     add_compile_options(-Wextra)
     # add_compile_options(-fno-exceptions)
     add_compile_options(-ffast-math)
-    add_compile_options(-fno-rtti)
     # add_compile_options(-fno-omit-frame-pointer)
 endif()
 
@@ -47,7 +46,9 @@ add_subdirectory(external/abseil-cpp)
 add_subdirectory(external/spdlog)
 add_subdirectory(external/Catch2)
 add_subdirectory(external/cxxopts)
+add_subdirectory(external/gsl-lite)
 add_subdirectory(external/benchmark)
+add_subdirectory(external/cnpy)
 
 # Download libsndfile
 if (WIN32)
@@ -106,6 +107,7 @@ set(TEST_SOURCES
     tests/BufferT.cpp
     tests/StereoBufferT.cpp
     tests/FilesT.cpp
+    tests/OnePoleFilterT.cpp
     tests/MainT.cpp
 )
 
@@ -121,8 +123,12 @@ target_link_libraries(sfzprint absl::strings cxxopts)
 ###############################
 # Basic command line program
 add_executable(sfizz sources/Main.cpp ${COMMON_SOURCES})
+if (HAVE_INTRIN_H OR HAVE_X86INTRIN_H)
+    target_sources(sfizz PRIVATE ${SSE_SOURCES})
+endif()
 # Per OS properties
 if(UNIX)
+    target_compile_options(sfizz PRIVATE -fno-rtti)
     target_link_libraries(sfizz stdc++fs)
 endif(UNIX)
 target_link_libraries(sfizz absl::strings cxxopts sndfile absl::flat_hash_map readerwriterqueue)
@@ -131,33 +137,37 @@ target_link_libraries(sfizz absl::strings cxxopts sndfile absl::flat_hash_map re
 # Test application
 add_executable(sfizz_tests ${TEST_SOURCES} ${COMMON_SOURCES})
 # Per OS properties
+if (HAVE_INTRIN_H OR HAVE_X86INTRIN_H)
+    target_sources(sfizz_tests PRIVATE ${SSE_SOURCES})
+endif()
 if(UNIX)
-target_link_libraries(sfizz_tests stdc++fs)
+    target_link_libraries(sfizz_tests stdc++fs)
 endif(UNIX)
-target_link_libraries(sfizz_tests Catch2::Catch2 absl::strings absl::flat_hash_map sndfile readerwriterqueue)
+target_link_libraries(sfizz_tests Catch2::Catch2 absl::strings absl::flat_hash_map sndfile readerwriterqueue cnpy-static gsl::gsl-lite)
 target_include_directories(sfizz_tests SYSTEM PRIVATE sources)
 file(COPY "tests" DESTINATION ${CMAKE_BINARY_DIR})
 
 ###############################
-add_executable(bench_fill benchmarks/Stereo_Fill.cpp ${COMMON_SOURCES})
+add_executable(bench_fill benchmarks/Stereo_Fill.cpp sources/StereoBufferSSE.cpp)
 # Per OS properties
-if(UNIX)
-    target_link_libraries(bench_fill stdc++fs)
-endif(UNIX)
-target_link_libraries(bench_fill absl::strings benchmark)
+target_link_libraries(bench_fill benchmark)
 
 ###############################
 add_executable(bench_read benchmarks/Stereo_Read_Interleaved.cpp sources/StereoBufferSSE.cpp)
 # Per OS properties
-if(UNIX)
-    target_link_libraries(bench_read stdc++fs)
-endif(UNIX)
-target_link_libraries(bench_read absl::strings benchmark)
+target_link_libraries(bench_read benchmark)
 
 ###############################
 add_executable(bench_write benchmarks/Stereo_Write_Interleaved.cpp sources/StereoBufferSSE.cpp)
 # Per OS properties
-if(UNIX)
-    target_link_libraries(bench_write stdc++fs)
-endif(UNIX)
-target_link_libraries(bench_write absl::strings benchmark)
+target_link_libraries(bench_write benchmark)
+
+###############################
+add_executable(bench_span benchmarks/Spans.cpp)
+# Per OS properties
+target_link_libraries(bench_span benchmark gsl::gsl-lite absl::span)
+
+###############################
+add_executable(bench_opf_high_vs_low benchmarks/OPF_high_vs_low.cpp)
+# Per OS properties
+target_link_libraries(bench_opf_high_vs_low benchmark gsl::gsl-lite)
diff --git a/benchmarks/OPF_high_vs_low.cpp b/benchmarks/OPF_high_vs_low.cpp
new file mode 100644
index 00000000..f8e0fa27
--- /dev/null
+++ b/benchmarks/OPF_high_vs_low.cpp
@@ -0,0 +1,168 @@
+#include <benchmark/benchmark.h>
+#include "gsl/gsl-lite.hpp"
+#include <random>
+#include <algorithm>
+#include "../sources/Intrinsics.h"
+
+constexpr float filterGain { 0.25f };
+
+void lowpass(gsl::span<const float> input, gsl::span<float> lowpass, float gain)
+{
+    float state = 0.0f;
+    float intermediate;
+    const auto G = gain / (1 - gain);
+    for (auto [in, out] = std::make_pair(input.begin(), lowpass.begin()); 
+         in < input.end() && out < lowpass.end();
+         in++, out++)
+    {
+        intermediate = G * (*in - state);
+        *out = intermediate + state;
+        state = *out + intermediate;
+    }
+}
+
+void highpass(gsl::span<const float> input, gsl::span<float> highpass, float gain)
+{
+    float state = 0.0f;
+    float intermediate;
+    const auto G = gain / (1 - gain);
+    for (auto [in, out] = std::make_pair(input.begin(), highpass.begin()); 
+         in < input.end() && out < highpass.end();
+         in++, out++)
+    {
+        intermediate = G * (*in - state);
+        *out = *in - intermediate - state;
+        state += 2*intermediate;
+    }
+}
+
+void highpass_foreach(gsl::span<const float> input, gsl::span<float> highpass, float gain)
+{
+    lowpass(input, highpass, gain);
+    for (auto [in, out] = std::make_pair(input.begin(), highpass.begin()); 
+         in < input.end() && out < highpass.end();
+         in++, out++)
+        *out = *in - *out;
+}
+
+void highpass_raw(gsl::span<const float> input, gsl::span<float> highpass, float gain)
+{
+    lowpass(input, highpass, gain);
+    auto in = input.data();
+    auto out = highpass.data();
+    while (in < input.end() && out < highpass.end())
+    {
+        *out = *in - *out;
+        out++;
+        in++;
+    }
+}
+
+void highpass_sse(gsl::span<const float> input, gsl::span<float> highpass, float gain)
+{
+    lowpass(input, highpass, gain);
+    auto in = input.data();
+    auto out = highpass.data();
+    constexpr int FloatAlignment { 4 };
+    const auto inputAlignedEnd = input.data() + (input.size() - (input.size() & (FloatAlignment - 1)));
+    const auto outputAlignedEnd = highpass.data() + (highpass.size() - (highpass.size() & (FloatAlignment - 1)));
+    while (in < inputAlignedEnd && out < outputAlignedEnd)
+    {
+        const auto inputRegister = _mm_loadu_ps(in);
+        auto outputRegister = _mm_loadu_ps(out);
+        outputRegister = _mm_sub_ps(inputRegister, outputRegister);
+        _mm_storeu_ps(out, outputRegister);
+        in += 4;
+        out += 4;
+    }
+    while (in < input.end() && out < highpass.end())
+    {
+        *out = *in - *out;
+        out++;
+        in++;
+    }
+}
+
+
+static void Low(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+        lowpass(input, output, filterGain);
+}
+
+static void High(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+        highpass(input, output, filterGain);
+}
+
+static void High_ForEach(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+        highpass_foreach(input, output, filterGain);
+}
+
+static void High_Raw(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+        highpass_raw(input, output, filterGain);
+}
+
+static void High_SSE(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+        highpass_sse(input, output, filterGain);
+}
+
+
+BENCHMARK(Low)->RangeMultiplier(2)->Range((2<<5), (2<<10));
+BENCHMARK(High)->RangeMultiplier(2)->Range((2<<5), (2<<10));
+BENCHMARK(High_ForEach)->RangeMultiplier(2)->Range((2<<5), (2<<10));
+BENCHMARK(High_Raw)->RangeMultiplier(2)->Range((2<<5), (2<<10));
+BENCHMARK(High_SSE)->RangeMultiplier(2)->Range((2<<5), (2<<10));
+BENCHMARK_MAIN();
\ No newline at end of file
diff --git a/benchmarks/Spans.cpp b/benchmarks/Spans.cpp
new file mode 100644
index 00000000..f537462c
--- /dev/null
+++ b/benchmarks/Spans.cpp
@@ -0,0 +1,111 @@
+#include <benchmark/benchmark.h>
+#include "gsl/gsl-lite.hpp"
+#include "absl/types/span.h"
+#include <random>
+#include <algorithm>
+
+constexpr float filterGain { 0.25f };
+
+void processRaw(float* input, float* lowpass, float gain, int numSamples)
+{
+    const auto end = input + numSamples;
+    float state = 0.0f;
+    float intermediate;
+    const auto G = gain / (1 - gain);
+    while (input < end)
+    {
+        intermediate = G * (*input++ - state);
+        *lowpass = intermediate + state;
+        state = *lowpass++ + intermediate;
+    }
+}
+
+void processGSLSpan(gsl::span<const float> input, gsl::span<float> lowpass, float gain)
+{
+
+    float state = 0.0f;
+    float intermediate;
+    const auto G = gain / (1 - gain);
+    for (auto [in, out] = std::make_pair(input.begin(), lowpass.begin()); 
+         in < input.end() && out < lowpass.end();
+         in++, out++)
+    {
+        intermediate = G * (*in - state);
+        *out = intermediate + state;
+        state = *out + intermediate;
+    }
+}
+
+void processABSLSpan(absl::Span<const float> input, absl::Span<float> lowpass, float gain)
+{
+
+    float state = 0.0f;
+    float intermediate;
+    const auto G = gain / (1 - gain);
+    for (auto [in, out] = std::make_pair(input.begin(), lowpass.begin()); 
+         in < input.end() && out < lowpass.end();
+         in++, out++)
+    {
+        intermediate = G * (*in - state);
+        *out = intermediate + state;
+        state = *out + intermediate;
+    }
+}
+
+static void Raw(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+    {
+        processRaw(input.data(), output.data(), filterGain, state.range(0));
+    }
+}
+
+static void GSLSpan(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+    {
+        processGSLSpan(input, output, filterGain);
+    }
+}
+
+static void ABSLSpan(benchmark::State& state) {
+    std::vector<float> input(state.range(0));
+    std::vector<float> output(state.range(0));
+    std::random_device rd { };
+    std::mt19937 gen { rd() };
+    
+    std::normal_distribution<float> dist { };
+    std::generate(input.begin(), input.end(), [&]() {
+        return dist(gen);
+    });
+
+    for (auto _ : state)
+    {
+        processABSLSpan(input, absl::MakeSpan(output), filterGain);
+    }
+}
+
+// Register the function as a benchmark
+
+BENCHMARK(Raw)->RangeMultiplier(2)->Range((2<<6), (2<<12));
+BENCHMARK(GSLSpan)->RangeMultiplier(2)->Range((2<<6), (2<<12));
+BENCHMARK(ABSLSpan)->RangeMultiplier(2)->Range((2<<6), (2<<12));
+BENCHMARK_MAIN();
\ No newline at end of file
diff --git a/external/cnpy b/external/cnpy
new file mode 160000
index 00000000..4e8810b1
--- /dev/null
+++ b/external/cnpy
@@ -0,0 +1 @@
+Subproject commit 4e8810b1a8637695171ed346ce68f6984e585ef4
diff --git a/external/gsl-lite b/external/gsl-lite
new file mode 160000
index 00000000..df36f637
--- /dev/null
+++ b/external/gsl-lite
@@ -0,0 +1 @@
+Subproject commit df36f6378336280043d7e06d8013e6fa4af6abd7
diff --git a/old/StateVariableFilter.cpp b/old/StateVariableFilter.cpp
new file mode 100644
index 00000000..11e1311f
--- /dev/null
+++ b/old/StateVariableFilter.cpp
@@ -0,0 +1,35 @@
+#include "StateVariableFilter.h"
+#include <tuple>
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP>::process<float>(const float& input [[maybe_unused]])
+// {
+//     return 0.0;
+// }
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP_LP>::process<float>(const float& input [[maybe_unused]])
+// {
+//     return std::make_pair<float, float>(0.0, 0.0);
+// }
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP_LP_HP>::process<float>(const float& input [[maybe_unused]])
+// {
+//     return std::make_tuple<float, float, float>(0.0, 0.0, 0.0);
+// }
+
+template<>
+auto StateVariableFilter::process(const float& input [[maybe_unused]], float& bandpass [[maybe_unused]]) 
+{
+
+}
+
+template<>
+auto StateVariableFilter::process(const float& input [[maybe_unused]], float& bandpass [[maybe_unused]], float& lowpass [[maybe_unused]]) 
+{
+    
+}
\ No newline at end of file
diff --git a/old/StateVariableFilter.h b/old/StateVariableFilter.h
new file mode 100644
index 00000000..ceb3620b
--- /dev/null
+++ b/old/StateVariableFilter.h
@@ -0,0 +1,27 @@
+#pragma once
+#include "Globals.h"
+#include <tuple>
+#include <array>
+
+// enum class SVFReturn { BP_LP_HP, BP_LP, BP};
+
+// template<SVFReturn ReturnType = SVFReturn::BP>
+class StateVariableFilter
+{
+public:
+    StateVariableFilter() = default;
+    StateVariableFilter(float R, float gain)
+    : R(R), gain(gain)
+    {
+
+    }
+
+    // Only use specializations
+    template<class InputType, class... OutputTypes>
+    auto process(const InputType& input, OutputTypes... outputs) = delete;
+    
+private:
+    std::array<float, 2> state;
+    float R { 0.0 };
+    float gain { 1.0 };
+};
\ No newline at end of file
diff --git a/old/StateVariableFilterSSE.cpp b/old/StateVariableFilterSSE.cpp
new file mode 100644
index 00000000..b8a51306
--- /dev/null
+++ b/old/StateVariableFilterSSE.cpp
@@ -0,0 +1,36 @@
+#include "StateVariableFilter.h"
+#include <tuple>
+#include "Intrinsics.h"
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP>::process<__m128>(const __m128& input [[maybe_unused]])
+// {
+//     return 0.0;
+// }
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP_LP>::process<__m128>(const __m128& input [[maybe_unused]])
+// {
+//     return std::make_pair<float, float>(0.0, 0.0);
+// }
+
+// template<>
+// template<>
+// auto StateVariableFilter<SVFReturn::BP_LP_HP>::process<__m128>(const __m128& input [[maybe_unused]])
+// {
+//     return std::make_tuple<float, float, float>(0.0, 0.0, 0.0);
+// }
+
+template<>
+auto StateVariableFilter::process(const __m128& input [[maybe_unused]], __m128& bandpass [[maybe_unused]]) 
+{
+
+}
+
+template<>
+auto StateVariableFilter::process(const __m128& input [[maybe_unused]], __m128& bandpass [[maybe_unused]], __m128& lowpass [[maybe_unused]]) 
+{
+
+}
\ No newline at end of file
diff --git a/sources/FilePool.h b/sources/FilePool.h
index 424d2b4a..2fd826db 100644
--- a/sources/FilePool.h
+++ b/sources/FilePool.h
@@ -8,7 +8,7 @@
 #include <string_view>
 #include <absl/container/flat_hash_map.h>
 #include <map>
-#include <readerwriterqueue.h>
+#include "readerwriterqueue.h"
 #include <thread>
 
 namespace sfz
diff --git a/sources/OnePoleFilter.h b/sources/OnePoleFilter.h
new file mode 100644
index 00000000..d8a64383
--- /dev/null
+++ b/sources/OnePoleFilter.h
@@ -0,0 +1,94 @@
+#include "Globals.h"
+#include <cmath>
+#include "gsl/gsl-lite.hpp"
+
+template<class Type=float>
+class OnePoleFilter
+{
+public:
+    OnePoleFilter() = default;
+    // Normalized cutoff with respect to the sampling rate
+    template<class C>
+    static Type normalizedGain(Type cutoff, C sampleRate)
+    {
+        return std::tan( cutoff / static_cast<Type>(sampleRate) * M_PIf32 );
+    }
+    
+    OnePoleFilter(Type gain)
+    {
+        setGain(gain);
+    }
+
+    void setGain(Type gain)
+    {
+        this->gain = gain;
+        G = gain / ( 1 + gain);
+    }
+
+    Type getGain() const { return gain; }
+
+    int processLowpass(gsl::span<const Type> input, gsl::span<Type> lowpass)
+    {
+        for (auto [in, out] = std::pair(input.begin(), lowpass.begin()); 
+            in < input.end() && out < lowpass.end(); in++, out++)
+        {
+            oneLowpass(in, out);
+        }
+        return std::min(input.size(), lowpass.size());
+    }
+
+    int processHighpass(gsl::span<const Type> input, gsl::span<Type> highpass)
+    {
+        for (auto [in, out] = std::pair(input.begin(), highpass.begin()); 
+            in < input.end() && out < highpass.end(); in++, out++)
+        {
+            oneHighpass(in, out);
+        }
+        return std::min(input.size(), highpass.size());
+    }
+
+    int processLowpassVariableGain(gsl::span<const Type> input, gsl::span<Type> lowpass, gsl::span<const Type> gain)
+    {
+        for (auto [in, out, g] = std::tuple(input.begin(), lowpass.begin(), gain.begin()); 
+            in < input.end() && out < lowpass.end() && g < gain.end(); in++, out++, g++)
+        {
+            setGain(*g);
+            oneLowpass(in, out);
+        }
+        
+        return std::min({ input.size(), lowpass.size(), gain.size() });
+    }
+
+    int processHighpassVariableGain(gsl::span<const Type> input, gsl::span<Type> highpass, gsl::span<const Type> gain)
+    {
+        for (auto [in, out, g] = std::tuple(input.begin(), highpass.begin(), gain.begin()); 
+            in < input.end() && out < highpass.end() && g < gain.end(); in++, out++, g++)
+        {
+            setGain(*g);
+            oneHighpass(in, out);
+        }
+        
+        return std::min({ input.size(), highpass.size(), gain.size() });
+    }
+
+    void reset() { state = 0.0; }
+private:
+    Type state { 0.0 };
+    Type gain { 0.25 };
+    Type intermediate { 0.0 };
+    Type G { gain / (1 + gain) };
+    
+    inline void oneLowpass(const Type* in, Type* out)
+    {
+        intermediate = G * (*in - state);
+        *out = intermediate + state;
+        state = *out + intermediate;
+    }
+
+    inline void oneHighpass(const Type* in, Type* out)
+    {
+        intermediate = G * (*in - state);
+        *out = *in - intermediate - state;
+        state += 2*intermediate;
+    }
+};
\ No newline at end of file
diff --git a/tests/OnePoleFilterT.cpp b/tests/OnePoleFilterT.cpp
new file mode 100644
index 00000000..1d29efdb
--- /dev/null
+++ b/tests/OnePoleFilterT.cpp
@@ -0,0 +1,102 @@
+#include "../sources/OnePoleFilter.h"
+#include "catch2/catch.hpp"
+#include "cnpy.h"
+#include "gsl/gsl-lite.hpp"
+#include <string>
+#include <filesystem>
+using namespace Catch::literals;
+
+template<class Type>
+void testInputOutput(const std::filesystem::path& inputNumpyFile, const std::filesystem::path& outputNumpyFile, Type gain)
+{
+    const auto input = cnpy::npy_load(inputNumpyFile.string());
+    REQUIRE( input.word_size == 8 );
+    const auto inputSpan = gsl::make_span(input.data<double>(), input.shape[0]);
+
+    const auto output = cnpy::npy_load(outputNumpyFile.string());
+    REQUIRE( output.word_size == 8 );
+    const auto outputSpan = gsl::make_span(output.data<double>(), output.shape[0]);
+    auto size = std::min(outputSpan.size(), inputSpan.size());
+    REQUIRE( size > 0 );
+
+    std::vector<Type> inputData;
+    std::vector<Type> expectedData;
+    inputData.reserve(size);
+    expectedData.reserve(size);
+    for (auto& data: inputSpan)
+        inputData.push_back(static_cast<Type>(data));
+    for (auto& data: outputSpan)
+        expectedData.push_back(static_cast<Type>(data));
+    
+    OnePoleFilter filter { gain };
+    std::vector<Type> outputData (size);
+    filter.processLowpass(inputData, outputData);
+    for (size_t i = 0; i < size; ++i)
+        REQUIRE( outputData[i] == Approx(expectedData[i]) );
+
+    filter.reset();
+    std::fill(outputData.begin(), outputData.end(), 0.0);
+    std::vector<Type> gains(size);
+    std::fill(gains.begin(), gains.end(), gain);
+    filter.processLowpassVariableGain(inputData, outputData, gains);
+    for (size_t i = 0; i < size; ++i)
+        REQUIRE( outputData[i] == Approx(expectedData[i]) );
+}
+
+TEST_CASE("[OnePoleFilter] Float")
+{
+    testInputOutput<float>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.1.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.1.npy",
+        0.1f
+    );
+    testInputOutput<float>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.3.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.3.npy",
+        0.3f
+    );
+    testInputOutput<float>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.5.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.5.npy",
+        0.5f
+    );
+    testInputOutput<float>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.7.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.7.npy",
+        0.7f
+    );
+    testInputOutput<float>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.9.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.9.npy",
+        0.9f
+    );
+}
+
+TEST_CASE("[OnePoleFilter] Double")
+{
+    testInputOutput<double>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.1.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.1.npy",
+        0.1f
+    );
+    testInputOutput<double>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.3.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.3.npy",
+        0.3f
+    );
+    testInputOutput<double>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.5.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.5.npy",
+        0.5f
+    );
+    testInputOutput<double>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.7.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.7.npy",
+        0.7f
+    );
+    testInputOutput<double>(
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_input_gain_0.9.npy",
+        std::filesystem::current_path() / "tests/TestFiles/OnePoleFilter/OPF_output_gain_0.9.npy",
+        0.9f
+    );
+}
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