diff --git a/src/Makefile b/src/Makefile
index c6da4ac..0e96de3 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -7,7 +7,7 @@ DEBUG=1
 INSTALL_DIR=/zynthian/zynthian-plugins/lv2
 INSTALL_MYPLUGINS_DIR=/zynthian/zynthian-my-data/presets/lv2
 
-OBJ=fm_core.o env.o lfo.o dx7note.o sin.o pitchenv.o fm_op_kernel.o freqlut.o exp2.o EngineMkI.o EngineOpl.o PluginFx.o trace.o
+OBJ=fm_core.o env.o lfo.o dx7note.o sin.o pitchenv.o fm_op_kernel.o freqlut.o exp2.o EngineMkI.o EngineOpl.o PluginFx.o trace.o porta.o
 
 CXXFLAGS_LVTK=$(shell pkg-config --cflags lvtk-plugin-2)
 CXXFLAGS+=-fPIC -DPIC -std=c++11 -I. $(CXXFLAGS_LVTK) -DLVTK_DEBUG=false
@@ -130,5 +130,7 @@ EngineOpl.o: Makefile EngineOpl.cpp
 PluginFx.o: Makefile PluginFx.cpp
 	$(CXX) $(CXXFLAGS) -Wall -c PluginFx.cpp
 
+porta.o: Makefile porta.cpp
+	$(CXX) $(CXXFLAGS) -Wall -c porta.cpp
 dexed_ttl.h: Dexed.ttl
 	ttl2c Dexed.ttl dexed_ttl.h
diff --git a/src/dexed.cpp b/src/dexed.cpp
index 1164b1b..f9af126 100644
--- a/src/dexed.cpp
+++ b/src/dexed.cpp
@@ -30,6 +30,7 @@
 #include "PluginFx.h"
 #include <unistd.h>
 #include <limits.h>
+#include "porta.h"
 
 Dexed::Dexed(double rate) : lvtk::Synth<DexedVoice, Dexed>(p_n_ports, p_midi_in)
 {
@@ -46,6 +47,7 @@ Dexed::Dexed(double rate) : lvtk::Synth<DexedVoice, Dexed>(p_n_ports, p_midi_in)
   Lfo::init(rate);
   PitchEnv::init(rate);
   Env::init_sr(rate);
+  Porta::init_sr(rate);
   fx.init(rate);
 
   engineMkI=new EngineMkI;
diff --git a/src/porta.cpp b/src/porta.cpp
new file mode 100644
index 0000000..f32b22a
--- /dev/null
+++ b/src/porta.cpp
@@ -0,0 +1,35 @@
+/*
+   Copyright 2019 Jean Pierre Cimalando.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+#include <math.h>
+#include "porta.h"
+#include "msfa/synth.h"
+
+void Porta::init_sr(double sampleRate)
+{
+  // compute portamento for CC 7-bit range
+
+  for (unsigned int i = 0; i < 128; ++i) {
+    // number of semitones travelled
+    double sps = 350.0 * pow(2.0, -0.062 * i);  // per second
+    double spf = sps / sampleRate;              // per frame
+    double spp = spf * N;                       // per period
+    const int step = (1 << 24) / 12;
+    rates[i] = (int32_t)(0.5f + step * spp);    // to pitch units
+  }
+}
+
+int32_t Porta::rates[128];
diff --git a/src/porta.h b/src/porta.h
new file mode 100644
index 0000000..d8a6b8c
--- /dev/null
+++ b/src/porta.h
@@ -0,0 +1,28 @@
+/*
+   Copyright 2019 Jean Pierre Cimalando.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+        http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+#ifndef SYNTH_PORTA_H_
+#define SYNTH_PORTA_H_
+
+#include <stdint.h>
+
+struct Porta {
+  public:
+    static void init_sr(double sampleRate);
+    static int32_t rates[128];
+};
+
+#endif  // SYNTH_PORTA_H_