diff --git a/APU.cpp b/APU.cpp
index 4ed3d23..7db2979 100644
--- a/APU.cpp
+++ b/APU.cpp
@@ -1,10 +1,12 @@
 #include "APU.h"
 #include <SDL2/SDL.h>
+#include "audio_viewer.h"
 
 namespace APU
 {
-    #define AUDIO_BUFFER_SIZE 2048
-    const float cycles_per_sample = 4194304.0f / 11025.0f;
+    #define SAMPLING_FREQ 44100
+    #define AUDIO_BUFFER_SIZE 8192
+    const float cycles_per_sample = 4194304.0f / SAMPLING_FREQ;
 
     SDL_AudioDeviceID sdlAudioDevice;
     uint8_t sound_buffer[AUDIO_BUFFER_SIZE];
@@ -22,6 +24,8 @@ namespace APU
 
     #define apu_enabled (NR52&0x80)
     #define DAC1_enabled ((NR12&0xf8)!=0)
+    #define DAC2_enabled ((NR22&0xf8)!=0)
+    #define DAC3_enabled ((NR30&0x80)!=0)
 
     uint8_t duty_cycles[4][8] = {
         {1, 1, 1, 1, 1, 1, 1, 0},
@@ -54,6 +58,7 @@ namespace APU
     uint8_t NR22 = 0; // 0xff17 - Sound channel 2 volume & envelope
     uint8_t NR23 = 0; // 0xff18 - Sound channel 2 period low
     uint8_t NR24 = 0; // 0xff19 - Sound channel 2 period high & control
+
     uint8_t NR30 = 0; // 0xff1a - Sound channel 3 DAC enable
     uint8_t NR31 = 0; // 0xff1b - Sound channel 3 length timer
     uint8_t NR32 = 0; // 0xff1c - Sound channel 3 output level
@@ -91,10 +96,11 @@ namespace APU
 
     void init()
     {
-        SDL_AudioSpec audioSpec{11025, AUDIO_U8, 1, 0, AUDIO_BUFFER_SIZE>>2, 0, 0, &audioCallback, NULL};
+        SDL_AudioSpec audioSpec{SAMPLING_FREQ, AUDIO_U8, 1, 0, AUDIO_BUFFER_SIZE>>2, 0, 0, &audioCallback, NULL};
         sdlAudioDevice = SDL_OpenAudioDevice(NULL, 0, &audioSpec, NULL, 0);
         resume();
         //samples_time=SDL_GetTicks();
+        audio_viewer::init();
     }
 
     void reset()
@@ -133,6 +139,26 @@ namespace APU
         // sweep does several things (check documentation)
     }
 
+    void triggerCH2()
+    {
+        CH2.enabled = true;
+        CH2.length_timer=NR21&0x3f;
+        CH2.period_divider = NR23 | ((NR24 &0x7)<<8);
+        // envelope timer is reset
+        CH2.volume = NR22>>4;
+        // sweep does several things (check documentation)
+    }
+
+    void triggerCH3()
+    {
+        CH3.enabled = true;
+        CH3.length_timer=NR31;
+        CH3.period_divider = NR33 | ((NR34 &0x7)<<8);
+        // envelope timer is reset
+        CH3.volume = (NR32>>5)&0x3;
+        // sweep does several things (check documentation)
+    }
+
     uint8_t readRegister(uint16_t address)
     {
         switch(address)
@@ -143,9 +169,37 @@ namespace APU
             case 0xff13: return 0x00; break;
             case 0xff14: return NR14 & 0x40; break;
 
+            case 0xff16: return NR21 & 0xc0; break;
+            case 0xff17: return NR22; break;
+            case 0xff18: return 0x00; break;
+            case 0xff19: return NR24 & 0x40; break;
+
+            case 0xff1a: return NR30; break;
+            case 0xff1b: return 0x00; break;
+            case 0xff1c: return NR32; break;
+            case 0xff1d: return 0x00; break;
+            case 0xff1e: return NR34 & 0x40; break;
+
             case 0xff24: return NR50; break;
             case 0xff25: return NR51; break;
             case 0xff26: return NR52; break;
+
+            case 0xff30: return WaveRAM[0]; break;
+            case 0xff31: return WaveRAM[1]; break;
+            case 0xff32: return WaveRAM[2]; break;
+            case 0xff33: return WaveRAM[3]; break;
+            case 0xff34: return WaveRAM[4]; break;
+            case 0xff35: return WaveRAM[5]; break;
+            case 0xff36: return WaveRAM[6]; break;
+            case 0xff37: return WaveRAM[7]; break;
+            case 0xff38: return WaveRAM[8]; break;
+            case 0xff39: return WaveRAM[9]; break;
+            case 0xff3a: return WaveRAM[10]; break;
+            case 0xff3b: return WaveRAM[11]; break;
+            case 0xff3c: return WaveRAM[12]; break;
+            case 0xff3d: return WaveRAM[13]; break;
+            case 0xff3e: return WaveRAM[14]; break;
+            case 0xff3f: return WaveRAM[15]; break;
         }
         return 0x00;
     }
@@ -162,9 +216,37 @@ namespace APU
             case 0xff13: NR13 = value; break;
             case 0xff14: NR14 = value; CH1.length_enable=(value&0x40); if (value&0x80) triggerCH1(); break;
 
+            case 0xff16: NR21 = value; CH2.length_timer=NR21&0x3f; CH2.duty_cycle = NR21>>6; break;
+            case 0xff17: NR22 = value; break;
+            case 0xff18: NR23 = value; break;
+            case 0xff19: NR24 = value; CH2.length_enable=(value&0x40); if (value&0x80) triggerCH2(); break;
+
+            case 0xff1a: NR30 = value; break;
+            case 0xff1b: NR31 = value; CH3.length_timer=NR31; break;
+            case 0xff1c: NR32 = value; break;
+            case 0xff1d: NR33 = value; break;
+            case 0xff1e: NR34 = value; CH3.length_enable=(value&0x40); if (value&0x80) triggerCH3(); break;
+
             case 0xff24: NR50 = value; break;
             case 0xff25: NR51 = value; break;
             case 0xff26: if (value&0x80) reset(); NR52 = (value&0x80) | (NR52 & 0x0f); break;
+
+            case 0xff30: WaveRAM[0] = value; break;
+            case 0xff31: WaveRAM[1] = value; break;
+            case 0xff32: WaveRAM[2] = value; break;
+            case 0xff33: WaveRAM[3] = value; break;
+            case 0xff34: WaveRAM[4] = value; break;
+            case 0xff35: WaveRAM[5] = value; break;
+            case 0xff36: WaveRAM[6] = value; break;
+            case 0xff37: WaveRAM[7] = value; break;
+            case 0xff38: WaveRAM[8] = value; break;
+            case 0xff39: WaveRAM[9] = value; break;
+            case 0xff3a: WaveRAM[10] = value; break;
+            case 0xff3b: WaveRAM[11] = value; break;
+            case 0xff3c: WaveRAM[12] = value; break;
+            case 0xff3d: WaveRAM[13] = value; break;
+            case 0xff3e: WaveRAM[14] = value; break;
+            case 0xff3f: WaveRAM[15] = value; break;
         }
     }
 
@@ -179,9 +261,27 @@ namespace APU
         if (DIVAPU_length==2) {
             DIVAPU_length=0;
             if (CH1.enabled && CH1.length_enable) {
-                CH1.length_timer++;
-                if (CH1.length_timer==0) {
+                if (CH1.length_timer==63) {
                     CH1.enabled = false;
+                    CH1.length_timer=0;
+                } else {
+                    CH1.length_timer++;
+                }
+            }
+            if (CH2.enabled && CH2.length_enable) {
+                if (CH2.length_timer==63) {
+                    CH2.enabled = false;
+                    CH2.length_timer=0;
+                } else {
+                    CH2.length_timer++;
+                }
+            }
+            if (CH3.enabled && CH3.length_enable) {
+                if (CH3.length_timer==255) {
+                    CH3.enabled = false;
+                    CH3.length_timer = 0;
+                } else {
+                    CH3.length_timer++;
                 }
             }
         }
@@ -204,12 +304,24 @@ namespace APU
                     }
                 }
             }
+            if ( CH2.enabled && (NR22&0x7) ) {   // If sweep pace != 0, envelope sweep is enabled
+                CH2.envelope_sweep_timer++;
+                if ( CH2.envelope_sweep_timer == (NR22&0x07) ) {    // if timer == envelope sweep, increase or decrease volume
+                    CH2.envelope_sweep_timer=0;
+                    if (NR22&0x8) {    // bit set increases, reset decreases
+                        if (CH2.volume<0x0f) CH2.volume++;
+                    } else {
+                        if (CH2.volume>0) CH2.volume--;
+                    }
+                }
+            }
 
             // Do the envelope sweep thing
         }
     }
 
     uint32_t dots = 0;
+    uint32_t dotsCH3 = 0;
     void update(uint32_t dt)
     {
         dots += dt;
@@ -221,30 +333,46 @@ namespace APU
                 CH1.duty_step++;
                 if (CH1.duty_step==8) CH1.duty_step=0;
             }
+            CH2.period_divider++;
+            if (CH2.period_divider==2048) {
+                CH2.period_divider = NR23 | ((NR24 &0x7)<<8);
+                CH2.duty_step++;
+                if (CH2.duty_step==8) CH2.duty_step=0;
+            }
+        }
+        dotsCH3 += dt;
+        while (dotsCH3>=2) {
+            dotsCH3 -= 2;
+            CH3.period_divider++;
+            if (CH3.period_divider==2048) {
+                CH3.period_divider = NR33 | ((NR34 &0x7)<<8);
+                CH3.duty_step++;
+                if (CH3.duty_step==32) CH3.duty_step=0;
+            }
         }
 
         t_sound += dt;
         samples_t += dt;
         if (t_sound>=cycles_per_sample) {
             t_sound-=cycles_per_sample;
-            //samples_generated++;
-            /*if (samples_t >=z80::getClock()) {
-                //printf("%i\n", samples_generated);
-                samples_generated=0;
-                samples_t = 0;
-            }*/
-            /*if (SDL_GetTicks()>=samples_time+1000) {
-                printf("%i\n", samples_generated);
-                samples_generated=0;
-                samples_time = SDL_GetTicks();
-            }*/
-            //sound_pos = (sound_pos+1) & 0x3ff;
-            //sound_buffer[sound_pos] = ear*128;
 
-            //if (sound_pos>=AUDIO_BUFFER_SIZE) sound_pos = last_1 = 0;
-            uint8_t sample = 0;
-            if (apu_enabled && DAC1_enabled) sample = (duty_cycles[CH1.duty_cycle][CH1.duty_step]*CH1.volume)<<2;
+            uint16_t sampleCH1 = 0;
+            if (apu_enabled && DAC1_enabled) sampleCH1 = (duty_cycles[CH1.duty_cycle][CH1.duty_step]*CH1.volume)<<2;
+
+            uint16_t sampleCH2 = 0;
+            if (apu_enabled && DAC2_enabled) sampleCH2 = (duty_cycles[CH2.duty_cycle][CH2.duty_step]*CH2.volume)<<2;
+
+            uint16_t sampleCH3 = 0;
+            if (apu_enabled && DAC3_enabled) {
+                uint8_t step = CH3.duty_step>>1;
+                uint8_t actual_sample = (CH3.duty_step&1 ? WaveRAM[step]&0x0f : WaveRAM[step]>>4)<<2;
+                sampleCH3 = CH3.volume==0 ? 0 : CH3.volume==1 ? actual_sample : CH3.volume==2 ? actual_sample>>1 : actual_sample>>2;
+            }
+
+            uint8_t sample = (sampleCH1+sampleCH2+sampleCH3)&0xff;
+
             sound_buffer[(sound_pos++)&(AUDIO_BUFFER_SIZE-1)] = sample;
+            audio_viewer::addsample(sample);
             //if (ear) last_1 = sound_pos;
         }
      }
diff --git a/audio_viewer.cpp b/audio_viewer.cpp
new file mode 100644
index 0000000..e07c0ab
--- /dev/null
+++ b/audio_viewer.cpp
@@ -0,0 +1,39 @@
+#include "audio_viewer.h"
+#include <SDL2/SDL.h>
+
+#define NUM_SAMPLES 256
+#define MAX_VOLUME  256
+namespace audio_viewer
+{
+    SDL_Window *win = nullptr;
+    SDL_Renderer *ren = nullptr;
+    //SDL_Texture *tex = nullptr;
+    uint8_t buffer[NUM_SAMPLES];
+    uint8_t pos = 0;
+    uint8_t screen[NUM_SAMPLES*MAX_VOLUME];
+
+    void init()
+    {
+        win = SDL_CreateWindow("Audio viewer", 1, 1, 256, 256, SDL_WINDOW_SHOWN);
+        ren = SDL_CreateRenderer(win, -1, 0);
+        //tex = SDL_CreateTexture(ren, SDL_PIXELFORMAT_ARGB8888, SDL_TEXTUREACCESS_STREAMING, 256, 256);
+        for (int i=0; i<NUM_SAMPLES; ++i) buffer[i] = 0;
+    }
+
+    void addsample(uint8_t sample)
+    {
+        buffer[pos] = sample;
+        pos = (pos+1)%NUM_SAMPLES;
+    }
+
+    void refresh()
+    {
+        SDL_SetRenderDrawColor(ren, 0, 0, 0, 0);
+        SDL_RenderClear(ren);
+        SDL_SetRenderDrawColor(ren, 255, 255, 255, 255);
+        for (int i=0; i<NUM_SAMPLES;++i) {
+            SDL_RenderDrawLine(ren, i, buffer[(pos+i)%NUM_SAMPLES], i+1, buffer[(pos+i+1)%NUM_SAMPLES]);
+        }
+        SDL_RenderPresent(ren);
+    }
+}
diff --git a/audio_viewer.h b/audio_viewer.h
new file mode 100644
index 0000000..6e54660
--- /dev/null
+++ b/audio_viewer.h
@@ -0,0 +1,9 @@
+#pragma once
+#include <stdint.h>
+
+namespace audio_viewer
+{
+    void init();
+    void addsample(uint8_t sample);
+    void refresh();
+}
diff --git a/gbscreen.cpp b/gbscreen.cpp
index 4d54c86..9773506 100644
--- a/gbscreen.cpp
+++ b/gbscreen.cpp
@@ -1,6 +1,7 @@
 #include "gbscreen.h"
 #include "sm83.h"
 #include "mem.h"
+#include "audio_viewer.h"
 //#include "zx_ula.h"
 #include <SDL2/SDL.h>
 #include "ui_window.h"
@@ -418,7 +419,7 @@ namespace gbscreen
             if (fullscreen) SDL_GetWindowSize(win, &rect.w, &rect.h);
             SDL_RenderFillRect(ren, &rect);
         }
-
+        audio_viewer::refresh();
     }
 
     void present()
diff --git a/mem.cpp b/mem.cpp
index 9d34f4e..91d8487 100644
--- a/mem.cpp
+++ b/mem.cpp
@@ -127,7 +127,7 @@ namespace mem
         } else {
             if (address==0xFF00) {
                 hram[address - 0XFE00] = getKeypad(hram[address - 0XFE00]);
-            } else if (address>=0xFF10 && address<=0xFF26) { return APU::readRegister(address); }
+            } else if (address>=0xFF10 && address<=0xFF3F) { return APU::readRegister(address); }
             return hram[address - 0XFE00];
         }
     }
@@ -156,7 +156,7 @@ namespace mem
                 hram[address-0xFE00] = value;
                 sm83::processInterrupts();
                 return;
-            } else if (address>=0xFF10 && address<=0xFF26) {    // APU
+            } else if (address>=0xFF10 && address<=0xFF3F) {    // APU
                 APU::writeRegister(address, value);
                 return;
             } else if ( (address==0xFF46) ) {                   // OAM DMA