Thomas Gulde pointed out that if the order in the setup

command is less than the max order then the output
is zero. That's fixed now in that if the order is lower
that the remaining biquads are now initialised as the
identity operation.
It would be better to actually run the loop only
through the biquads which have proper coefficients
but that's not accessible because of the template
mess. Would require a lot of re-writing to merge
memory and coefficient classes.

CMakeLists.txt

@@ -5,11 +5,11 @@ if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
 endif()
 
 if(${CMAKE_VERSION} VERSION_LESS "3.0.0")
-	set(PROJECT_VERSION 1.7.6)
+	set(PROJECT_VERSION 1.7.7)
 	project(iir)
 else()
 	cmake_policy(SET CMP0048 NEW) # set VERSION in project()
-	project(iir VERSION 1.7.6 LANGUAGES CXX)
+	project(iir VERSION 1.7.7 LANGUAGES CXX)
 endif()
 include(GNUInstallDirs)
 add_subdirectory(test)

iir/Biquad.h

@@ -153,12 +153,12 @@ namespace Iir {
 		void applyScale (double scale);
 
 	public:
-		double m_a0;
-		double m_a1;
-		double m_a2;
-		double m_b1;
-		double m_b2;
-		double m_b0;
+		double m_a0 = 1;
+		double m_a1 = 0;
+		double m_a2 = 0;
+		double m_b1 = 0;
+		double m_b2 = 0;
+		double m_b0 = 1;
 	};
 
 //------------------------------------------------------------------------------

iir/Cascade.cpp

@@ -106,6 +106,10 @@ namespace Iir {
 			throw std::invalid_argument("Number of stages is larger than the max stages.");
 
 		Biquad* stage = m_stageArray;
+		for (int i = 0; i < m_maxStages; ++i, ++stage)
+			stage->setIdentity();
+
+		stage = m_stageArray;
 		for (int i = 0; i < m_numStages; ++i, ++stage)
 			stage->setPoleZeroPair (proto[i]);