diff --git a/libs/ardour/ardour/iec1ppmdsp.h b/libs/ardour/ardour/iec1ppmdsp.h
index 58dea97555..39bedaa06a 100644
--- a/libs/ardour/ardour/iec1ppmdsp.h
+++ b/libs/ardour/ardour/iec1ppmdsp.h
@@ -28,7 +28,7 @@ public:
     Iec1ppmdsp (void);
     ~Iec1ppmdsp (void);
 
-    void process (float *p, int n);  
+    void process (float const *p, int n);  
     float read (void);
     void reset ();
 
diff --git a/libs/ardour/ardour/iec2ppmdsp.h b/libs/ardour/ardour/iec2ppmdsp.h
index 3574a8bd3f..a335a72fd0 100644
--- a/libs/ardour/ardour/iec2ppmdsp.h
+++ b/libs/ardour/ardour/iec2ppmdsp.h
@@ -28,7 +28,7 @@ public:
     Iec2ppmdsp (void);
     ~Iec2ppmdsp (void);
 
-    void process (float *p, int n);  
+    void process (float const *p, int n);  
     float read (void);
     void reset ();
 
diff --git a/libs/ardour/ardour/kmeterdsp.h b/libs/ardour/ardour/kmeterdsp.h
index eca3c76695..69d1215b98 100644
--- a/libs/ardour/ardour/kmeterdsp.h
+++ b/libs/ardour/ardour/kmeterdsp.h
@@ -27,7 +27,7 @@ public:
     Kmeterdsp (void);
     ~Kmeterdsp (void);
 
-    void process (float *p, int n);
+    void process (float const *p, int n);
     float read ();
     void reset ();
 
diff --git a/libs/ardour/ardour/vumeterdsp.h b/libs/ardour/ardour/vumeterdsp.h
index 86487e8e8e..e588126105 100644
--- a/libs/ardour/ardour/vumeterdsp.h
+++ b/libs/ardour/ardour/vumeterdsp.h
@@ -28,7 +28,7 @@ public:
     Vumeterdsp (void);
     ~Vumeterdsp (void);
 
-    void process (float *p, int n);  
+    void process (float const *p, int n);  
     float read (void);
     void reset ();
 
diff --git a/libs/ardour/iec1ppmdsp.cc b/libs/ardour/iec1ppmdsp.cc
index 79a572da1c..842d33b8b5 100644
--- a/libs/ardour/iec1ppmdsp.cc
+++ b/libs/ardour/iec1ppmdsp.cc
@@ -41,7 +41,7 @@ Iec1ppmdsp::~Iec1ppmdsp (void)
 }
 
 
-void Iec1ppmdsp::process (float *p, int n)
+void Iec1ppmdsp::process (float const *p, int n)
 {
     float z1, z2, m, t;
 
diff --git a/libs/ardour/iec2ppmdsp.cc b/libs/ardour/iec2ppmdsp.cc
index caca744c52..d65f51b3fa 100644
--- a/libs/ardour/iec2ppmdsp.cc
+++ b/libs/ardour/iec2ppmdsp.cc
@@ -41,7 +41,7 @@ Iec2ppmdsp::~Iec2ppmdsp (void)
 }
 
 
-void Iec2ppmdsp::process (float *p, int n)
+void Iec2ppmdsp::process (float const *p, int n)
 {
     float z1, z2, m, t;
 
diff --git a/libs/ardour/kmeterdsp.cc b/libs/ardour/kmeterdsp.cc
index 35c95c2daf..add026797d 100644
--- a/libs/ardour/kmeterdsp.cc
+++ b/libs/ardour/kmeterdsp.cc
@@ -42,7 +42,7 @@ void Kmeterdsp::init (int fsamp)
     _omega = 9.72f / fsamp; // ballistic filter coefficient
 }
 
-void Kmeterdsp::process (float *p, int n)
+void Kmeterdsp::process (float const *p, int n)
 {
     // Called by JACK's process callback.
     //
diff --git a/libs/ardour/vumeterdsp.cc b/libs/ardour/vumeterdsp.cc
index a3d0ec23c1..7b70286754 100644
--- a/libs/ardour/vumeterdsp.cc
+++ b/libs/ardour/vumeterdsp.cc
@@ -39,7 +39,7 @@ Vumeterdsp::~Vumeterdsp (void)
 }
 
 
-void Vumeterdsp::process (float *p, int n)
+void Vumeterdsp::process (float const *p, int n)
 {
     float z1, z2, m, t1, t2;