diff --git a/include/sdsp/casc2orderIIR.h b/include/sdsp/casc2orderIIR.h
index d2b00eb..853d8e4 100644
--- a/include/sdsp/casc2orderIIR.h
+++ b/include/sdsp/casc2orderIIR.h
@@ -10,6 +10,8 @@ class casc2orderIIR {
 private:
     int pos{ 0 };
 
+    double gain{ 1.0 };
+
     std::array<std::array<double, 3>, M + 1> mem{ 0 };
 
     std::array<std::array<double, 3>, M> bCoeff{ 0 };
@@ -39,7 +41,7 @@ class casc2orderIIR {
         std::array<std::array<double, 3>, M> a = aCoeff;
 
         while (begin < end) {
-            y.at(0).at(p) = *begin;
+            y.at(0).at(p) = *begin * gain;
 
             int d1{ p - j1 };
             if (d1 < 0)
@@ -69,8 +71,9 @@ class casc2orderIIR {
         mem = y;
     }
 
-    void SetBPCoeff(double f0, double fs, double Q)
+    void SetBPCoeff(double f0, double fs, double Q, double gainIn = 1.0)
     {
+        gain = gainIn;
         double q2{ 2 * Q };
         fType = FilterType::BandPass;
 
@@ -124,8 +127,9 @@ class casc2orderIIR {
         }
     }
 
-    void SetHPCoeff(double f0, double fs)
+    void SetHPCoeff(double f0, double fs, double gainIn = 1.0)
     {
+        gain = gainIn;
         fType = FilterType::HighPass;
 
         double e0{ 2 * M_PI * f0 / fs };
@@ -149,8 +153,9 @@ class casc2orderIIR {
         }
     }
 
-    void SetLPCoeff(double f0, double fs)
+    void SetLPCoeff(double f0, double fs, double gainIn = 1.0)
     {
+        gain = gainIn;
         fType = FilterType::LowPass;
 
         double e0{ 2 * M_PI * f0 / fs };
diff --git a/test/testIIR.cpp b/test/testIIR.cpp
index 6134e5b..a49476c 100644
--- a/test/testIIR.cpp
+++ b/test/testIIR.cpp
@@ -76,6 +76,100 @@ TEST_CASE("Filter test")
         }
     }
 
+    SECTION("Test the LP filter gain")
+    {
+        constexpr double fs{ 100e3 };
+        constexpr double f0{ 10e3 };
+
+        std::array<double, 1024> impulse1{ 0 };
+        impulse1.at(0) = 1.0;
+        std::array<double, 1024> impulse2{ 0 };
+        impulse2.at(0) = 1.0;
+
+        sdsp::casc2orderIIR<4> df;
+        df.SetLPCoeff(f0, fs);
+
+        sdsp::casc2orderIIR<4> df2;
+        df2.SetLPCoeff(f0, fs, 2.0);
+
+        df.Process(impulse1.begin(), impulse1.end());
+        df2.Process(impulse2.begin(), impulse2.end());
+
+        auto times_two = [](double &n) { n = 2.0 * n; };
+        std::for_each(impulse1.begin(), impulse1.end(), times_two);
+
+        std::array<double, 1024> error{ 0 };
+
+        for (size_t i = 0; i < error.size(); i++) {
+            error.at(i) = std::abs(impulse1.at(i) - impulse2.at(i));
+        }
+        double maxError = *std::max_element(error.begin(), error.end());
+        REQUIRE(maxError < 1e-12);
+    }
+
+    SECTION("Test the HP filter gain")
+    {
+        constexpr double fs{ 100e3 };
+        constexpr double f0{ 10e3 };
+
+        std::array<double, 1024> impulse1{ 0 };
+        impulse1.at(0) = 1.0;
+        std::array<double, 1024> impulse2{ 0 };
+        impulse2.at(0) = 1.0;
+
+        sdsp::casc2orderIIR<4> df;
+        df.SetHPCoeff(f0, fs);
+
+        sdsp::casc2orderIIR<4> df2;
+        df2.SetHPCoeff(f0, fs, 2.0);
+
+        df.Process(impulse1.begin(), impulse1.end());
+        df2.Process(impulse2.begin(), impulse2.end());
+
+        auto times_two = [](double &n) { n = 2.0 * n; };
+        std::for_each(impulse1.begin(), impulse1.end(), times_two);
+
+        std::array<double, 1024> error{ 0 };
+
+        for (size_t i = 0; i < error.size(); i++) {
+            error.at(i) = std::abs(impulse1.at(i) - impulse2.at(i));
+        }
+        double maxError = *std::max_element(error.begin(), error.end());
+        REQUIRE(maxError < 1e-12);
+    }
+
+    SECTION("Test the BP filter gain")
+    {
+        constexpr double fs{ 100e3 };
+        constexpr double f0{ 10e3 };
+        constexpr double Q{ 1.1 };
+
+        std::array<double, 1024> impulse1{ 0 };
+        impulse1.at(0) = 1.0;
+        std::array<double, 1024> impulse2{ 0 };
+        impulse2.at(0) = 1.0;
+
+        sdsp::casc2orderIIR<4> df;
+        df.SetBPCoeff(f0, fs, Q);
+
+        sdsp::casc2orderIIR<4> df2;
+        df2.SetBPCoeff(f0, fs, Q, 2.0);
+
+        df.Process(impulse1.begin(), impulse1.end());
+        df2.Process(impulse2.begin(), impulse2.end());
+
+        auto times_two = [](double &n) { n = 2.0 * n; };
+        std::for_each(impulse1.begin(), impulse1.end(), times_two);
+
+        std::array<double, 1024> error{ 0 };
+
+        for (size_t i = 0; i < error.size(); i++) {
+            error.at(i) = std::abs(impulse1.at(i) - impulse2.at(i));
+        }
+        double maxError = *std::max_element(error.begin(), error.end());
+        REQUIRE(maxError < 1e-12);
+    }
+
     SECTION("Test filter preload")
     {
         constexpr double fs{ 100e3 };