diff --git a/google-tests/CMakeLists.txt b/google-tests/CMakeLists.txt
index 6a7f103..2119c13 100644
--- a/google-tests/CMakeLists.txt
+++ b/google-tests/CMakeLists.txt
@@ -11,6 +11,10 @@ include_directories(${gtest_SOURCE_DIR}/include ${gtest_SOURCE_DIR} libnpy/inclu
 add_executable(Google_Tests_run test1.cpp)
 
 file(COPY test1/data1.npy DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/test1)
+file(COPY test1/iir_t1_a.npy DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/test1)
+file(COPY test1/iir_t1_b.npy DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/test1)
+file(COPY test1/iir_t1_x.npy DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/test1)
+file(COPY test1/iir_t1_y.npy DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/test1)
 
 target_link_libraries(Google_Tests_run pasada)
 #target_include_directories(Google_Tests_run PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/pasada-lib/include")
diff --git a/google-tests/test1.cpp b/google-tests/test1.cpp
index f576e76..c9fd64d 100644
--- a/google-tests/test1.cpp
+++ b/google-tests/test1.cpp
@@ -3,6 +3,7 @@
 //
 #include <gtest/gtest.h>
 #include "library.h"
+#include "iir_filter.h"
 #include "npy.hpp"
 #include <utility>
 #include <vector>
@@ -51,76 +52,6 @@ TEST(HelloTest, Save_npy_matrix) {
     npy::write_npy(path, d);
 }
 
-/** Shift register implemented as a circular buffer. */
-class Buf {
-protected:
-    std::vector<double> data;
-    size_t size;
-    size_t n;
-public:
-    Buf(size_t N): size(N), n(0) {
-        data.resize(N);
-        data.assign(N, 0.0);
-    }
-    void push(double val) {
-        data[n] = val;
-        n = (n+1) % size;
-    }
-};
-
-/** Running filter base. */
-class Filt : Buf {
-protected:
-    std::vector<double> taps;
-    size_t shift;
-    size_t offset;
-public:
-    Filt(size_t N, size_t shift, size_t offset, std::vector<double> taps): Buf(N), shift(shift), offset(offset), taps(taps) {
-        if (taps.size() != N) throw std::invalid_argument("taps.size() != N");
-    }
-    double filter(double val) {
-        this->push(val);
-        return this->peek();
-    }
-    double peek() {
-        double sum = 0;
-        for (size_t i = offset; i < this->size; i++) {
-            //size_t n = (this->n - i + shift - 1) % this->size; // unsigned % size ... bad if u is negative
-            size_t n = (this->size + this->n - i + shift - 1) % this->size;
-            //std::cout << " t[" << i << "] * v[" << n << "]" << std::endl;
-            sum += this->data[n] * this->taps[i];
-        }
-        return sum;
-    }
-    void push(double val) {
-        Buf::push(val);
-    }
-};
-
-class IirFilter {
-protected:
-    Filt y;
-    Filt x;
-public:
-    IirFilter(std::vector<double> b, std::vector<double> a) : x(b.size(), 0, 0, b), y(a.size(), 1, 1, a) {
-        if (b.size() != a.size()) throw std::invalid_argument("b.size() != a.size()");
-    }
-    double filter(double val) {
-        //std::cout << "x.filter(" << val << ")" << std::endl;
-        double xv = x.filter(val);
-        //std::cout << "xv=" << xv << std::endl;
-        //std::cout << "y.peek()" << std::endl;
-        double yv = y.peek();
-        //std::cout << "yv=" << yv << std::endl;
-        //std::cout << "---" << std::endl;
-        double yo = xv - yv;
-        y.push(yo);
-        return yo;
-    }
-};
-
-// TODO: copy npy files from CMake output folder
-// TODO: add npy files to CMakeLists.txt so they are copied into output folder
 TEST(HelloTest, Test_IIR_1_Apply_IIR) {
     npy::npy_data x = npy::read_npy<double>("test1/iir_t1_x.npy");
     npy::npy_data y_e = npy::read_npy<double>("test1/iir_t1_y.npy");
diff --git a/google-tests/test1/iir_t1_a.npy b/google-tests/test1/iir_t1_a.npy
new file mode 100644
index 0000000..63e37c1
Binary files /dev/null and b/google-tests/test1/iir_t1_a.npy differ
diff --git a/google-tests/test1/iir_t1_b.npy b/google-tests/test1/iir_t1_b.npy
new file mode 100644
index 0000000..9d18c84
Binary files /dev/null and b/google-tests/test1/iir_t1_b.npy differ
diff --git a/google-tests/test1/iir_t1_x.npy b/google-tests/test1/iir_t1_x.npy
new file mode 100644
index 0000000..d6351a5
Binary files /dev/null and b/google-tests/test1/iir_t1_x.npy differ
diff --git a/google-tests/test1/iir_t1_y.npy b/google-tests/test1/iir_t1_y.npy
new file mode 100644
index 0000000..9a4d017
Binary files /dev/null and b/google-tests/test1/iir_t1_y.npy differ
diff --git a/pasada-lib/CMakeLists.txt b/pasada-lib/CMakeLists.txt
index 22a82a8..64f1494 100644
--- a/pasada-lib/CMakeLists.txt
+++ b/pasada-lib/CMakeLists.txt
@@ -2,6 +2,7 @@ project(Pasada_Lib)
 
 SET(PASADA_SRC
         library.cpp
+        iir_filter.cpp
 )
 
 if(PASADA_BUILD_TESTS)
diff --git a/pasada-lib/iir_filter.cpp b/pasada-lib/iir_filter.cpp
new file mode 100644
index 0000000..6c308b5
--- /dev/null
+++ b/pasada-lib/iir_filter.cpp
@@ -0,0 +1,51 @@
+//
+// Created by david on 02.03.2026.
+//
+
+#include "iir_filter.h"
+
+Buf::Buf(size_t N): size(N), n(0) {
+    data.resize(N);
+    data.assign(N, 0.0);
+}
+void Buf::push(double val) {
+    data[n] = val;
+    n = (n+1) % size;
+}
+
+Filt::Filt(size_t N, size_t shift, size_t offset, std::vector<double> taps): Buf(N), shift(shift), offset(offset), taps(taps) {
+    if (taps.size() != N) throw std::invalid_argument("taps.size() != N");
+}
+double Filt::filter(double val) {
+    this->push(val);
+    return this->peek();
+}
+double Filt::peek() {
+    double sum = 0;
+    for (size_t i = offset; i < this->size; i++) {
+        //size_t n = (this->n - i + shift - 1) % this->size; // unsigned % size ... bad if u is negative
+        size_t n = (this->size + this->n - i + shift - 1) % this->size;
+        //std::cout << " t[" << i << "] * v[" << n << "]" << std::endl;
+        sum += this->data[n] * this->taps[i];
+    }
+    return sum;
+}
+void Filt::push(double val) {
+    Buf::push(val);
+}
+
+IirFilter::IirFilter(std::vector<double> b, std::vector<double> a) : x(b.size(), 0, 0, b), y(a.size(), 1, 1, a) {
+    if (b.size() != a.size()) throw std::invalid_argument("b.size() != a.size()");
+}
+double IirFilter::filter(double val) {
+    //std::cout << "x.filter(" << val << ")" << std::endl;
+    double xv = x.filter(val);
+    //std::cout << "xv=" << xv << std::endl;
+    //std::cout << "y.peek()" << std::endl;
+    double yv = y.peek();
+    //std::cout << "yv=" << yv << std::endl;
+    //std::cout << "---" << std::endl;
+    double yo = xv - yv;
+    y.push(yo);
+    return yo;
+}
diff --git a/pasada-lib/include/iir_filter.h b/pasada-lib/include/iir_filter.h
new file mode 100644
index 0000000..b3fca5f
--- /dev/null
+++ b/pasada-lib/include/iir_filter.h
@@ -0,0 +1,46 @@
+//
+// Created by david on 02.03.2026.
+//
+
+#ifndef PASADASUPERPROJECT_IIR_FILTER_H
+#define PASADASUPERPROJECT_IIR_FILTER_H
+
+#include <utility>
+#include <vector>
+#include <stdexcept>
+
+/** Shift register implemented as a circular buffer. */
+class Buf {
+protected:
+    std::vector<double> data;
+    size_t size;
+    size_t n;
+public:
+    Buf(size_t N);
+    void push(double val);
+};
+
+/** Running filter base. */
+class Filt : Buf {
+protected:
+    std::vector<double> taps;
+    size_t shift;
+    size_t offset;
+public:
+    Filt(size_t N, size_t shift, size_t offset, std::vector<double> taps);
+    double filter(double val);
+    double peek();
+    void push(double val);
+};
+
+/** Running IIR filter. */
+class IirFilter {
+protected:
+    Filt y;
+    Filt x;
+public:
+    IirFilter(std::vector<double> b, std::vector<double> a);
+    double filter(double val);
+};
+
+#endif //PASADASUPERPROJECT_IIR_FILTER_H
\ No newline at end of file