1 files changed, 3 insertions, 3 deletions
diff --git a/src/audioinputengine.h b/src/audioinputengine.h
index b218086..1701864 100644
--- a/src/audioinputengine.h
+++ b/src/audioinputengine.h
@@ -38,11 +38,11 @@ class AudioInputEngine {
 public:
   virtual ~AudioInputEngine() {}
 
-  virtual bool isMidiEngine() { return false; } 
+  virtual bool isMidiEngine() const { return false; } 
 
-  virtual bool init(Instruments &instruments) = 0;
+  virtual bool init(const Instruments& instruments) = 0;
 
-  virtual void setParm(std::string parm, std::string value) = 0;
+  virtual void setParm(const std::string& parm, const std::string& value) = 0;
 
   virtual bool start() = 0;
   virtual void stop() = 0;