diff --git a/Open_Theremin_V3/Open_Theremin_V3.ino b/Open_Theremin_V3/Open_Theremin_V3.ino
index 4022591..b70f0b9 100644
--- a/Open_Theremin_V3/Open_Theremin_V3.ino
+++ b/Open_Theremin_V3/Open_Theremin_V3.ino
@@ -1,6 +1,8 @@
 /*
  *  Open Theremin V3 with MIDI interface control software for Arduino UNO 
  *  Based on Open Theremin V3 version 3.0  Copyright (C) 2010-2016 by Urs Gaudenz
+ *   
+ *  Also integrate changes from Open Theremin V3 Version 3.1  Copyright (C) 2010-2020 by Urs Gaudenz
  *
  *
  *  Open Theremin V3 with MIDI interface control software is free software: 
@@ -19,9 +21,10 @@
  *  the Open Theremin V3 with MIDI interface control software.  
  *  If not, see <http://www.gnu.org/licenses/>.
  *
- *  Urs Gaudenz also credits for their important contributions to Open Theremin V3: 
+ *  Also credited for their important contributions to Open Theremin V3: 
  *  David Harvey
  *  Michael Margolis
+ *  "Theremingenieur" Thierry Frenkel
  */
 
 /* Midi added by Vincent Dhamelincourt - September 2017. 
diff --git a/Open_Theremin_V3/SPImcpDAC.h b/Open_Theremin_V3/SPImcpDAC.h
new file mode 100644
index 0000000..e87f9e8
--- /dev/null
+++ b/Open_Theremin_V3/SPImcpDAC.h
@@ -0,0 +1,104 @@
+/* Control the mcp 4921/4922 DACs with hardware SPI of the Arduino UNO
+ * ...without all the overhead of the Arduino SPI lib...
+ * Just the needed functions in a runtime optimized way by "Theremingenieur" Thierry Frenkel
+ * This file is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef SPImcpDac_h
+#define SPImcpDac_h
+
+#include <Arduino.h>
+
+// Data direction & Port register & Bit number for DAC Latch:
+#define MCP_DAC_LDAC_DDR DDRD
+#define MCP_DAC_LDAC_PORT PORTD
+#define MCP_DAC_LDAC_BIT 7
+// Data direction & Port register & Bit number for DAC CS
+#define MCP_DAC_CS_DDR DDRB
+#define MCP_DAC_CS_PORT PORTB
+#define MCP_DAC_CS_BIT 2
+// Data direction & Port register & Bit number for DAC2 CS
+#define MCP_DAC2_CS_DDR DDRB
+#define MCP_DAC2_CS_PORT PORTB
+#define MCP_DAC2_CS_BIT 1
+// Data direction & Port registers & Bit numbers for Hardware SPI
+#define HW_SPI_DDR DDRB
+#define HW_SPI_SCK_BIT 5
+#define HW_SPI_MISO_BIT 4 // unused in this configuration
+#define HW_SPI_MOSI_BIT 3
+
+static inline void SPImcpDACinit()
+{
+	// initialize the latch pin:
+	MCP_DAC_LDAC_DDR |= _BV(MCP_DAC_LDAC_BIT);
+	MCP_DAC_LDAC_PORT |= _BV(MCP_DAC_LDAC_BIT);
+	// initialize the CS pins:
+	MCP_DAC_CS_DDR   |= _BV(MCP_DAC_CS_BIT);
+	MCP_DAC_CS_PORT  |= _BV(MCP_DAC_CS_BIT);
+	MCP_DAC2_CS_DDR  |= _BV(MCP_DAC2_CS_BIT);
+	MCP_DAC2_CS_PORT |= _BV(MCP_DAC2_CS_BIT);
+	// initialize the hardware SPI pins:
+	HW_SPI_DDR |= _BV(HW_SPI_SCK_BIT);
+	HW_SPI_DDR |= _BV(HW_SPI_MOSI_BIT);
+	// initialize the hardware SPI registers
+	SPCR = _BV(SPE) | _BV(MSTR);	// no interrupt, SPI enable, MSB first, SPI master, SPI mode 0, clock = f_osc/4 (maximum)
+	SPSR = _BV(SPI2X);  // double the SPI clock, ideally we get 8 MHz, so that a 16bit word goes out in 3.5us (5.6us when called from an interrupt) including CS asserting/deasserting
+}
+
+static inline void SPImcpDACtransmit(uint16_t data)
+{
+	// Send highbyte and wait for complete
+	SPDR = highByte(data);
+  asm("nop");
+	while (!(SPSR & _BV(SPIF)))
+		;
+	// Send lowbyte and wait for complete
+	SPDR = lowByte(data);
+  asm("nop");
+	while (!(SPSR & _BV(SPIF)))
+		;
+}
+
+static inline void SPImcpDAClatch()
+{
+	MCP_DAC_LDAC_PORT &= ~_BV(MCP_DAC_LDAC_BIT);
+	MCP_DAC_LDAC_PORT |= _BV(MCP_DAC_LDAC_BIT);
+}
+
+static inline void SPImcpDACsend(uint16_t data)
+{
+	MCP_DAC_CS_PORT &= ~_BV(MCP_DAC_CS_BIT);
+  // Sanitize input data and add DAC config MSBs
+  data &= 0x0FFF;
+  data |= 0x7000;
+	SPImcpDACtransmit(data);
+	MCP_DAC_CS_PORT |= _BV(MCP_DAC_CS_BIT);
+	// Do not latch immpediately, let's do it at the very beginning of the next interrupt to get consistent timing
+}
+
+static inline void SPImcpDAC2Asend(uint16_t data)
+{
+	MCP_DAC2_CS_PORT &= ~_BV(MCP_DAC2_CS_BIT);
+	// Sanitize input data and add DAC config MSBs
+	data &= 0x0FFF;
+	data |= 0x7000;
+	SPImcpDACtransmit(data);
+	MCP_DAC2_CS_PORT |= _BV(MCP_DAC2_CS_BIT);
+	SPImcpDAClatch();
+}
+
+static inline void SPImcpDAC2Bsend(uint16_t data)
+{
+	MCP_DAC2_CS_PORT &= ~_BV(MCP_DAC2_CS_BIT);
+	// Sanitize input data and add DAC config MSBs
+	data &= 0x0FFF;
+	data |= 0xF000;
+	SPImcpDACtransmit(data);
+	MCP_DAC2_CS_PORT |= _BV(MCP_DAC2_CS_BIT);
+	SPImcpDAClatch();
+}
+
+#endif
diff --git a/Open_Theremin_V3/application.cpp b/Open_Theremin_V3/application.cpp
index 69ade8f..b51bce0 100644
--- a/Open_Theremin_V3/application.cpp
+++ b/Open_Theremin_V3/application.cpp
@@ -196,7 +196,6 @@ AppMode Application::nextMode() {
 void Application::loop() {
   int32_t pitch_v = 0, pitch_l = 0;            // Last value of pitch  (for filtering)
   int32_t vol_v = 0,   vol_l = 0;              // Last value of volume (for filtering)
-  uint16_t tmpVolume;
 
   uint16_t volumePotValue = 0;
   uint16_t pitchPotValue = 0;
diff --git a/Open_Theremin_V3/ihandlers.cpp b/Open_Theremin_V3/ihandlers.cpp
index a4da417..32a1e4b 100644
--- a/Open_Theremin_V3/ihandlers.cpp
+++ b/Open_Theremin_V3/ihandlers.cpp
@@ -1,7 +1,7 @@
 #include "Arduino.h"
 
 #include "ihandlers.h"
-#include "mcpDac.h"
+#include "SPImcpDAC.h"
 #include "timer.h"
 
 #include "build.h"
@@ -15,7 +15,7 @@
 #include "theremin_sintable7.c"
 #include "theremin_sintable8.c"
 
-const int16_t* const wavetables[] PROGMEM = {
+const int16_t* const wavetables[] = { //Fixed following a suggestion by Michael Freitas, does not need to be in PROGMEM
   sine_table,
   sine_table2,
   sine_table3,
@@ -26,12 +26,12 @@ const int16_t* const wavetables[] PROGMEM = {
   sine_table8
 };
 
-static const uint32_t MCP_DAC_BASE = 2047;
+static const uint32_t MCP_DAC_BASE = 2048;
 
 #define INT0_STATE    (PIND & (1<<PORTD2))
 #define PC_STATE      (PINB & (1<<PORTB0))
 
-volatile uint8_t  vScaledVolume = 0;
+volatile uint16_t vScaledVolume = 0;
 volatile uint16_t vPointerIncrement = 0;
 
 volatile uint16_t pitch = 0;            // Pitch value
@@ -97,69 +97,38 @@ void ihInitialiseVolumeMeasurement() //Measurement of variable frequency oscilla
     
   }
 
-/* 16 bit by 8 bit multiplication */
-static inline uint32_t mul_16_8(uint16_t a, uint8_t b)
-{
-  uint32_t product;
-  asm (
-    "mul %A1, %2\n\t"
-    "movw %A0, r0\n\t"
-    "clr %C0\n\t"
-    "clr %D0\n\t"
-    "mul %B1, %2\n\t"
-    "add %B0, r0\n\t"
-    "adc %C0, r1\n\t"
-    "clr r1"
-    :
-    "=&r" (product)
-    :
-    "r" (a), "r" (b));
-  return product;
-}
 
 /* Externaly generated 31250 Hz Interrupt for WAVE generator (32us) */
 ISR (INT1_vect) {
-  // Interrupt takes up a total of max 25 us
+  // Interrupt takes up normally 14us but can take up to 22us when interrupted by another interrupt.
+
+  // Latch previously written DAC value:
+  SPImcpDAClatch();
 
   disableInt1(); // Disable External Interrupt INT1 to avoid recursive interrupts
   // Enable Interrupts to allow counter 1 interrupts
   interrupts();
 
   int16_t  waveSample;
-  uint32_t scaledSample;
+  uint32_t scaledSample=0;
   uint16_t offset = (uint16_t)(pointer>>6) & 0x3ff;
 
 #if CV_ENABLED                                 // Generator for CV output
 
  vPointerIncrement = min(vPointerIncrement, 4095);
- mcpDacSend(vPointerIncrement);        //Send result to Digital to Analogue Converter (audio out) (9.6 us)
+ SPImcpDACsend(vPointerIncrement);        //Send result to Digital to Analogue Converter (audio out) (5.5 us)
 
 #else   //Play sound
 
-  // Read next wave table value (3.0us)
-  // The slightly odd tactic here is to provide compile-time expressions for the wavetable
-  // positions. Making addr1 the index into the wavtables array breaks the time limit for
-  // the interrupt handler
-  switch (vWavetableSelector) {
-    case 1:  waveSample = (int16_t) pgm_read_word_near(wavetables[1] + offset); break;
-    case 2:  waveSample = (int16_t) pgm_read_word_near(wavetables[2] + offset); break;
-    case 3:  waveSample = (int16_t) pgm_read_word_near(wavetables[3] + offset); break;
-    case 4:  waveSample = (int16_t) pgm_read_word_near(wavetables[4] + offset); break;
-    case 5:  waveSample = (int16_t) pgm_read_word_near(wavetables[5] + offset); break;
-    case 6:  waveSample = (int16_t) pgm_read_word_near(wavetables[6] + offset); break;
-    case 7:  waveSample = (int16_t) pgm_read_word_near(wavetables[7] + offset); break;
-    default: waveSample = (int16_t) pgm_read_word_near(wavetables[0] + offset); break;
-  };
+  // Read next wave table value
+  waveSample = (int16_t)pgm_read_word_near(wavetables[vWavetableSelector] + offset);
+
+  scaledSample = ((int32_t)waveSample * (uint32_t)vScaledVolume) >> 16; // The compiler optimizes this better than any assembly written by hand !!!
 
-  if (waveSample > 0) {                   // multiply 16 bit wave number by 8 bit volume value (11.2us / 5.4us)
-    scaledSample = MCP_DAC_BASE + (mul_16_8(waveSample, vScaledVolume) >> 8);
-  } else {
-    scaledSample = MCP_DAC_BASE - (mul_16_8(-waveSample, vScaledVolume) >> 8);
-  }
 
-  mcpDacSend(scaledSample);        //Send result to Digital to Analogue Converter (audio out) (9.6 us)
+  SPImcpDACsend(scaledSample + MCP_DAC_BASE); //Send result to Digital to Analogue Converter (audio out) (5.5 us)
 
-  pointer = pointer + vPointerIncrement;    // increment table pointer (ca. 2us)
+  pointer += vPointerIncrement; // increment table pointer 
 
 #endif                          //CV play sound
   incrementTimer();               // update 32us timer
diff --git a/Open_Theremin_V3/ihandlers.h b/Open_Theremin_V3/ihandlers.h
index d6de5d0..07c3c71 100644
--- a/Open_Theremin_V3/ihandlers.h
+++ b/Open_Theremin_V3/ihandlers.h
@@ -3,7 +3,7 @@
 
 extern volatile uint16_t pitch;              // Pitch value
 extern volatile uint16_t vol;                // Volume value
-extern volatile uint8_t  vScaledVolume;      // Volume byte
+extern volatile uint16_t vScaledVolume;      // Volume byte
 
 extern volatile uint16_t pitch_counter;      // Pitch counter
 extern volatile uint16_t pitch_counter_l;    // Last value of pitch counter
@@ -41,4 +41,4 @@ void resetVolFlag();
 void savePitchCounter();
 void saveVolCounter();
 
-#endif // _IHANDLERS_H
+#endif // _IHANDLERS_H