diff --git a/third-party/Synth_Dexed/README.md b/third-party/Synth_Dexed/README.md
index bcedf2d..87b548e 100644
--- a/third-party/Synth_Dexed/README.md
+++ b/third-party/Synth_Dexed/README.md
@@ -1,2 +1,172 @@
-# synth_dexed
+# Synth_Dexed
 
+Synth_Dexed is a port of the Dexed sound engine
+(https://github.com/asb2m10/dexed) as library for the Teensy-3.5/3.6/4.x with
+an audio shield. Dexed ist heavily based on
+https://github.com/google/music-synthesizer-for-android .
+Synth_Dexed ist SYSEX compatible with a famous 6-OP FM synth and is used in MicroDexed (https://codeberg.org/dcoredump/MicroDexed).
+
+## License
+MicroDexed is licensed on the GPL v3. The msfa component (acronym for music synthesizer for android, see https://github.com/google/music-synthesizer-for-android) stays on the Apache 2.0 license to able to collaborate between projects.
+
+## Credits & thanks
+
+* Dexed engine by Pascal Gauthier (asb2m10)
+* DX Synth engine (as part of Dexed): Raph Levien and the msfa team
+* PPPlay : Great OPL3 implementation, with documented code :D
+* Thierry Pottier: for extreme testing, discussing about different options, images and many good suggestions for UI handling
+* Lars Pelz: Testing and documentation
+* Mark (@positionhigh) for testing
+
+## Usage
+
+See example sketch.
+
+## API
+
+    AudioSynthDexed(uint8_t max_notes, uint16_t sample_rate);
+
+    // Global methods
+    void activate(void);
+    void deactivate(void);
+    void setMonoMode(bool mode);
+    bool getMonoMode(void);
+    void setRefreshMode(bool mode);
+    bool getRefreshMode(void);
+    void setMaxNotes(uint8_t n);
+    uint8_t getMaxNotes(void);
+    void doRefreshVoice(void);
+    bool decodeVoice(uint8_t* encoded_data, uint8_t* data);
+    bool encodeVoice(uint8_t* encoded_data);
+    bool getVoiceData(uint8_t* data_copy);
+    void setVoiceDataElement(uint8_t address, uint8_t value);
+    uint8_t getVoiceDataElement(uint8_t address);
+    void loadInitVoice(void);
+    void loadVoiceParameters(uint8_t* data);
+    uint8_t getNumNotesPlaying(void);
+    uint32_t getXRun(void);
+    uint16_t getRenderTimeMax(void);
+    void resetRenderTimeMax(void);
+    void ControllersRefresh(void);
+
+    // Sound methods
+    void keyup(int16_t pitch);
+    void keydown(int16_t pitch, uint8_t velo);
+    void setSustain(bool sustain);
+    bool getSustain(void);
+    void panic(void);
+    void notesOff(void);
+    void resetControllers(void);
+    void setMasterTune(int8_t mastertune);
+    int8_t getMasterTune(void);
+    void setPortamentoMode(uint8_t portamento_mode, uint8_t portamento_glissando, uint8_t portamento_time);
+    void setPBController(uint8_t pb_range, uint8_t pb_step);
+    void setMWController(uint8_t mw_range, uint8_t mw_assign, uint8_t mw_mode);
+    void setFCController(uint8_t fc_range, uint8_t fc_assign, uint8_t fc_mode);
+    void setBCController(uint8_t bc_range, uint8_t bc_assign, uint8_t bc_mode);
+    void setATController(uint8_t at_range, uint8_t at_assign, uint8_t at_mode);
+    void setModWheel(uint8_t value);
+    uint8_t getModWheel(void);
+    void setBreathController(uint8_t value);
+    uint8_t getBreathController(void);
+    void setFootController(uint8_t value);
+    uint8_t getFootController(void);
+    void setAftertouch(uint8_t value);
+    uint8_t getAftertouch(void);
+    void setPitchbend(int16_t value);
+    int16_t getPitchbend(void);
+    void setPitchbendRange(uint8_t range);
+    uint8_t getPitchbendRange(void);
+    void setPitchbendStep(uint8_t step);
+    uint8_t getPitchbendStep(void);
+    void setModWheelRange(uint8_t range);
+    uint8_t getModWheelRange(void);
+    void setModWheelTarget(uint8_t target);
+    uint8_t getModWheelTarget(void);
+    void setFootControllerRange(uint8_t range);
+    uint8_t getFootControllerRange(void);
+    void setFootControllerTarget(uint8_t target);
+    uint8_t getFootControllerTarget(void);
+    void setBreathControllerRange(uint8_t range);
+    uint8_t getBreathControllerRange(void);
+    void setBreathControllerTarget(uint8_t target);
+    uint8_t getBreathControllerTarget(void);
+    void setAftertouchRange(uint8_t range);
+    uint8_t getAftertouchRange(void);
+    void setAftertouchTarget(uint8_t target);
+    uint8_t getAftertouchTarget(void);
+    void setFilterCutoff(float cutoff);
+    float getFilterCutoff(void);
+    void setFilterResonance(float resonance);
+    float getFilterResonance(void);
+    void setGain(float gain);
+    float getGain(void);
+
+    // Voice configuration methods
+    void setOPAll(uint8_t ops);
+    void setOP(uint8_t op, bool state);
+    bool getOP(uint8_t op);
+    void setOPRateAll(uint8_t rate);
+    void setOPLevelAll(uint8_t level);
+    void setOPRateAllCarrier(uint8_t step, uint8_t rate);
+    void setOPLevelAllCarrier(uint8_t step, uint8_t level);
+    void setOPRateAllModulator(uint8_t step, uint8_t rate);
+    void setOPLevelAllModulator(uint8_t step, uint8_t level);
+    void setOPRate(uint8_t op, uint8_t step, uint8_t rate);
+    uint8_t getOPRate(uint8_t op, uint8_t step);
+    void setOPLevel(uint8_t op, uint8_t step, uint8_t level);
+    uint8_t getOPLevel(uint8_t op, uint8_t step);
+    void setOPKeyboardLevelScalingBreakPoint(uint8_t op, uint8_t level);
+    uint8_t getOPKeyboardLevelScalingBreakPoint(uint8_t op);
+    void setOPKeyboardLevelScalingDepthLeft(uint8_t op, uint8_t depth);
+    uint8_t getOPKeyboardLevelScalingDepthLeft(uint8_t op);
+    void setOPKeyboardLevelScalingDepthRight(uint8_t op, uint8_t depth);
+    uint8_t getOPKeyboardLevelScalingDepthRight(uint8_t op);
+    void setOPKeyboardLevelScalingCurveLeft(uint8_t op, uint8_t curve);
+    uint8_t getOPKeyboardLevelScalingCurveLeft(uint8_t op);
+    void setOPKeyboardLevelScalingCurveRight(uint8_t op, uint8_t curve);
+    uint8_t getOPKeyboardLevelScalingCurveRight(uint8_t op);
+    void setOPKeyboardRateScale(uint8_t op, uint8_t scale);
+    uint8_t getOPKeyboardRateScale(uint8_t op);
+    void setOPAmpModulationSensity(uint8_t op, uint8_t sensitivity);
+    uint8_t getOPAmpModulationSensity(uint8_t op);
+    void setOPKeyboardVelocitySensity(uint8_t op, uint8_t sensitivity);
+    uint8_t getOPKeyboardVelocitySensity(uint8_t op);
+    void setOPOutputLevel(uint8_t op, uint8_t level);
+    uint8_t getOPOutputLevel(uint8_t op);
+    void setOPMode(uint8_t op, uint8_t mode);
+    uint8_t getOPMode(uint8_t op);
+    void setOPFrequencyCoarse(uint8_t op, uint8_t frq_coarse);
+    uint8_t getOPFrequencyCoarse(uint8_t op);
+    void setOPFrequencyFine(uint8_t op, uint8_t frq_fine);
+    uint8_t getOPFrequencyFine(uint8_t op);
+    void setOPDetune(uint8_t op, uint8_t detune);
+    uint8_t getOPDetune(uint8_t op);
+    void setPitchRate(uint8_t step, uint8_t rate);
+    uint8_t getPitchRate(uint8_t step);
+    void setPitchLevel(uint8_t step, uint8_t level);
+    uint8_t getPitchLevel(uint8_t step);
+    void setAlgorithm(uint8_t algorithm);
+    uint8_t getAlgorithm(void);
+    void setFeedback(uint8_t feedback);
+    uint8_t getFeedback(void);
+    void setOscillatorSync(bool sync);
+    bool getOscillatorSync(void);
+    void setLFOSpeed(uint8_t speed);
+    uint8_t getLFOSpeed(void);
+    void setLFODelay(uint8_t delay);
+    uint8_t getLFODelay(void);
+    void setLFOPitchModulationDepth(uint8_t depth);
+    uint8_t getLFOPitchModulationDepth(void);
+    void setLFOAmpModulationDepth(uint8_t delay);
+    uint8_t getLFOAmpModulationDepth(void);
+    void setLFOSync(bool sync);
+    bool getLFOSync(void);
+    void setLFOWaveform(uint8_t waveform);
+    uint8_t getLFOWaveform(void);
+    void setLFOPitchModulationSensitivity(uint8_t sensitivity);
+    uint8_t getLFOPitchModulationSensitivity(void);
+    void setTranspose(uint8_t transpose);
+    uint8_t getTranspose(void);
+    void setName(char* name);
+    void getName(char* buffer);
\ No newline at end of file
diff --git a/third-party/Synth_Dexed/examples/synth_dexed.ino b/third-party/Synth_Dexed/examples/synth_dexed.ino
index 8f89666..e3132af 100644
--- a/third-party/Synth_Dexed/examples/synth_dexed.ino
+++ b/third-party/Synth_Dexed/examples/synth_dexed.ino
@@ -15,7 +15,7 @@ uint8_t fmpiano_sysex[156] = {
   70, 77, 45, 80, 73, 65, 78, 79, 00, 00                                              // 10 * char for name ("DEFAULT   ")
 }; // FM-Piano
 
-AudioSynthDexed          dexed(SAMPLE_RATE);
+AudioSynthDexed          dexed(4,SAMPLE_RATE); // 4 voices max
 AudioOutputI2S           i2s1;
 AudioControlSGTL5000     sgtl5000_1;
 AudioConnection          patchCord1(dexed, 0, i2s1, 0);
diff --git a/third-party/Synth_Dexed/src/synth_dexed.cpp b/third-party/Synth_Dexed/src/synth_dexed.cpp
index dbd28f8..95b5de0 100644
--- a/third-party/Synth_Dexed/src/synth_dexed.cpp
+++ b/third-party/Synth_Dexed/src/synth_dexed.cpp
@@ -48,9 +48,6 @@
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
 
 */
-extern int perform_attack_mod;
-extern int perform_release_mod;
-
 const float dc = 1e-18;
 
 inline static float tptpc(float& state, float inp, float cutoff) {
@@ -594,7 +591,7 @@ void Dexed::doRefreshVoice(void)
   refreshVoice = true;
 }
 
-void Dexed::setOPs(uint8_t ops)
+void Dexed::setOPAll(uint8_t ops)
 {
   controllers.opSwitch = ops;
 }
diff --git a/third-party/Synth_Dexed/src/synth_dexed.h b/third-party/Synth_Dexed/src/synth_dexed.h
index 70a70f2..6a799d3 100644
--- a/third-party/Synth_Dexed/src/synth_dexed.h
+++ b/third-party/Synth_Dexed/src/synth_dexed.h
@@ -1156,7 +1156,7 @@ class Dexed
     void setMaxNotes(uint8_t n);
     uint8_t getMaxNotes(void);
     void doRefreshVoice(void);
-    void setOPs(uint8_t ops);
+    void setOPAll(uint8_t ops);
     bool decodeVoice(uint8_t* encoded_data, uint8_t* data);
     bool encodeVoice(uint8_t* encoded_data);
     bool getVoiceData(uint8_t* data_copy);