diff --git a/papers/doc/7-systems/nes.md b/papers/doc/7-systems/nes.md
index c9b4d024..37d4a703 100644
--- a/papers/doc/7-systems/nes.md
+++ b/papers/doc/7-systems/nes.md
@@ -19,7 +19,65 @@ also known as Famicom. it is a five-channel sound generator: first two channels
   - `x` is the time.
   - `y` is the shift.
   - set to 0 to disable it.
+- `15xx`: set envelope mode.
+  - `0`: envelope + length counter (volume represents envelope duration).
+  - `1`: length counter (volume represents output volume).
+  - `2`: looping envelope (volume represents envelope duration).
+  - `3`: constant volume (default; volume represents output volume).
+  - pulse and noise channels only.
+  - you may need to apply a phase reset (using the macro) to make the envelope effective.
+- `16xx`: set length counter.
+  - see table below for possible values.
+  - this will trigger phase reset.
+- `17xx`: set frame counter mode.
+  - `0`: 4-step.
+    - NTSC: 120Hz sweeps and lengths; 240Hz envelope.
+    - PAL: 100Hz sweeps and lengths; 200Hz envelope.
+    - Dendy: 118.9Hz sweeps and lengths; 237.8Hz envelope.
+  - `1`: 5-step.
+    - NTSC: 96Hz sweeps and lengths; 192Hz envelope.
+    - PAL: 80Hz sweeps and lengths; 160Hz envelope.
+    - Dendy: 95.1Hz sweeps and lengths; 190.2Hz envelope.
 - `18xx`: set PCM channel mode.
   - `00`: PCM (software).
   - `01`: DPCM (hardware).
   - when in DPCM mode, samples will sound muffled (due to its nature), availables pitches are limited and loop point is ignored.
+
+# length counter table
+
+val | raw | NTSC  | PAL   | Dendy | NTSC 5-step | PAL 5-step | Dendy 5-step
+----|-----|-------|-------|-------|-------------|------------|--------------
+ 00 |  10 | 83ms  | 100ms | 84ms  | 104ms       | 125ms      | 105ms
+ 01 | 254 | 2.1s  | 2.5s  | 2.1s  | 2.6s        | 3.2s       | 2.7s
+ 02 |  20 | 166ms | 200ms | 168ms | 208ms       | 250ms      | 210ms
+ 03 |   2 | 17ms  | 20ms  | 17ms  | 21ms        | 25ms       | 21ms
+ 04 |  40 | 333ms | 400ms | 336ms | 417ms       | 500ms      | 421ms
+ 05 |   4 | 33ms  | 40ms  | 34ms  | 42ms        | 50ms       | 42ms
+ 06 |  80 | 667ms | 800ms | 673ms | 833ms       | 1.0s       | 841ms
+ 07 |   6 | 50ms  | 60ms  | 50ms  | 63ms        | 75ms       | 63ms
+ 08 | 160 | 1.3s  | 1.6s  | 1.3s  | 1.7s        | 2.0s       | 1.7s
+ 09 |   8 | 67ms  | 80ms  | 67ms  | 83ms        | 100ms      | 84ms
+ 0A |  60 | 500ms | 600ms | 505ms | 625ms       | 750ms      | 631ms
+ 0B |  10 | 83ms  | 100ms | 84ms  | 104ms       | 125ms      | 105ms
+ 0C |  14 | 117ms | 140ms | 118ms | 146ms       | 175ms      | 147ms
+ 0D |  12 | 100ms | 120ms | 101ms | 125ms       | 150ms      | 126ms
+ 0E |  26 | 217ms | 260ms | 219ms | 271ms       | 325ms      | 273ms
+ 0F |  14 | 117ms | 140ms | 118ms | 145ms       | 175ms      | 147ms
+ 10 |  12 | 100ms | 120ms | 101ms | 125ms       | 150ms      | 126ms
+ 11 |  16 | 133ms | 160ms | 135ms | 167ms       | 200ms      | 168ms
+ 12 |  24 | 200ms | 240ms | 202ms | 250ms       | 300ms      | 252ms
+ 13 |  18 | 150ms | 180ms | 151ms | 188ms       | 225ms      | 189ms
+ 14 |  48 | 400ms | 480ms | 404ms | 500ms       | 600ms      | 505ms
+ 15 |  20 | 167ms | 200ms | 168ms | 208ms       | 250ms      | 210ms
+ 16 |  96 | 800ms | 960ms | 807ms | 1.0s        | 1.2s       | 1.0s
+ 17 |  22 | 183ms | 220ms | 185ms | 229ms       | 275ms      | 231ms
+ 18 | 192 | 1.6s  | 1.9s  | 1.6s  | 2.0s        | 2.4s       | 2.0s
+ 19 |  24 | 200ms | 240ms | 202ms | 250ms       | 300ms      | 252ms
+ 1A |  72 | 600ms | 720ms | 606ms | 750ms       | 900ms      | 757ms
+ 1B |  26 | 217ms | 260ms | 219ms | 271ms       | 325ms      | 273ms
+ 1C |  16 | 133ms | 160ms | 135ms | 167ms       | 200ms      | 168ms
+ 1D |  28 | 233ms | 280ms | 235ms | 292ms       | 350ms      | 294ms
+ 1E |  32 | 267ms | 320ms | 269ms | 333ms       | 400ms      | 336ms
+ 1F |  30 | 250ms | 300ms | 252ms | 313ms       | 375ms      | 315ms
+
+reference: [NESdev](https://www.nesdev.org/wiki/APU_Length_Counter)
diff --git a/src/engine/dispatch.h b/src/engine/dispatch.h
index 4c9fb2f2..0287f01c 100644
--- a/src/engine/dispatch.h
+++ b/src/engine/dispatch.h
@@ -205,6 +205,10 @@ enum DivDispatchCmds {
   DIV_CMD_SNES_ECHO_FEEDBACK,
   DIV_CMD_SNES_ECHO_FIR,
 
+  DIV_CMD_NES_ENV_MODE,
+  DIV_CMD_NES_LENGTH,
+  DIV_CMD_NES_COUNT_MODE,
+
   DIV_ALWAYS_SET_VOLUME, // () -> alwaysSetVol
 
   DIV_CMD_MAX
diff --git a/src/engine/platform/nes.cpp b/src/engine/platform/nes.cpp
index 72c217c8..47d81573 100644
--- a/src/engine/platform/nes.cpp
+++ b/src/engine/platform/nes.cpp
@@ -214,7 +214,7 @@ void DivPlatformNES::tick(bool sysTick) {
         rWrite(0x4000+i*4,(chan[i].outVol==0)?0:255);
         chan[i].freqChanged=true;
       } else {
-        rWrite(0x4000+i*4,0x30|chan[i].outVol|((chan[i].duty&3)<<6));
+        rWrite(0x4000+i*4,(chan[i].envMode<<4)|chan[i].outVol|((chan[i].duty&3)<<6));
       }
     }
     if (chan[i].std.arp.had) {
@@ -239,7 +239,7 @@ void DivPlatformNES::tick(bool sysTick) {
         }
       }
       if (i!=2) {
-        rWrite(0x4000+i*4,0x30|chan[i].outVol|((chan[i].duty&3)<<6));
+        rWrite(0x4000+i*4,(chan[i].envMode<<4)|chan[i].outVol|((chan[i].duty&3)<<6));
       }
       if (i==3) { // noise
         chan[i].freqChanged=true;
@@ -289,11 +289,11 @@ void DivPlatformNES::tick(bool sysTick) {
       }
       if (i==3) { // noise
         rWrite(0x4002+i*4,(chan[i].duty<<7)|chan[i].freq);
-        rWrite(0x4003+i*4,0xf0);
+        rWrite(0x4003+i*4,(chan[i].len<<3));
       } else {
         rWrite(0x4002+i*4,chan[i].freq&0xff);
         if ((chan[i].prevFreq>>8)!=(chan[i].freq>>8) || i==2) {
-          rWrite(0x4003+i*4,0xf8|(chan[i].freq>>8));
+          rWrite(0x4003+i*4,(chan[i].len<<3)|(chan[i].freq>>8));
         }
         if (chan[i].freq!=65535 && chan[i].freq!=0) {
           chan[i].prevFreq=chan[i].freq;
@@ -419,7 +419,7 @@ int DivPlatformNES::dispatch(DivCommand c) {
       if (c.chan==2) {
         rWrite(0x4000+c.chan*4,0xff);
       } else if (!parent->song.brokenOutVol2) {
-        rWrite(0x4000+c.chan*4,0x30|chan[c.chan].vol|((chan[c.chan].duty&3)<<6));
+        rWrite(0x4000+c.chan*4,(chan[c.chan].envMode<<4)|chan[c.chan].vol|((chan[c.chan].duty&3)<<6));
       }
       break;
     case DIV_CMD_NOTE_OFF:
@@ -451,7 +451,7 @@ int DivPlatformNES::dispatch(DivCommand c) {
           if (c.chan==2) {
             rWrite(0x4000+c.chan*4,0xff);
           } else {
-            rWrite(0x4000+c.chan*4,0x30|chan[c.chan].vol|((chan[c.chan].duty&3)<<6));
+            rWrite(0x4000+c.chan*4,(chan[c.chan].envMode<<4)|chan[c.chan].vol|((chan[c.chan].duty&3)<<6));
           }
         }
       }
@@ -491,7 +491,7 @@ int DivPlatformNES::dispatch(DivCommand c) {
       if (c.chan==3) { // noise
         chan[c.chan].freqChanged=true;
       } else if (c.chan<2) {
-        rWrite(0x4000+c.chan*4,0x30|(chan[c.chan].active?chan[c.chan].outVol:0)|((chan[c.chan].duty&3)<<6));
+        rWrite(0x4000+c.chan*4,(chan[c.chan].active?((chan[c.chan].envMode<<4)|chan[c.chan].outVol):0x30)|((chan[c.chan].duty&3)<<6));
       }
       break;
     case DIV_CMD_NES_SWEEP:
@@ -507,6 +507,24 @@ int DivPlatformNES::dispatch(DivCommand c) {
       }
       rWrite(0x4001+(c.chan*4),chan[c.chan].sweep);
       break;
+    case DIV_CMD_NES_ENV_MODE:
+      chan[c.chan].envMode=c.value&3;
+      if (c.chan==3) { // noise
+        chan[c.chan].freqChanged=true;
+      } else if (c.chan<2) {
+        rWrite(0x4000+c.chan*4,(chan[c.chan].active?((chan[c.chan].envMode<<4)|chan[c.chan].outVol):0x30)|((chan[c.chan].duty&3)<<6));
+      }
+      break;
+    case DIV_CMD_NES_LENGTH:
+      if (c.chan>=4) break;
+      chan[c.chan].len=c.value&0x1f;
+      chan[c.chan].freqChanged=true;
+      chan[c.chan].prevFreq=-1;
+      break;
+    case DIV_CMD_NES_COUNT_MODE:
+      countMode=c.value;
+      rWrite(0x4017,countMode?0x80:0);
+      break;
     case DIV_CMD_NES_DMC:
       rWrite(0x4011,c.value&0x7f);
       break;
@@ -572,6 +590,7 @@ void DivPlatformNES::forceIns() {
   }
   rWrite(0x4001,chan[0].sweep);
   rWrite(0x4005,chan[1].sweep);
+  rWrite(0x4017,countMode?0x80:0);
 }
 
 void* DivPlatformNES::getChanState(int ch) {
@@ -615,6 +634,7 @@ void DivPlatformNES::reset() {
   dpcmBank=0;
   dpcmMode=false;
   goingToLoop=false;
+  countMode=false;
 
   if (useNP) {
     nes1_NP->Reset();
diff --git a/src/engine/platform/nes.h b/src/engine/platform/nes.h
index ef4a9e72..16f52f20 100644
--- a/src/engine/platform/nes.h
+++ b/src/engine/platform/nes.h
@@ -28,7 +28,7 @@
 class DivPlatformNES: public DivDispatch {
   struct Channel {
     int freq, baseFreq, pitch, pitch2, prevFreq, note, ins;
-    unsigned char duty, sweep;
+    unsigned char duty, sweep, envMode, len;
     bool active, insChanged, freqChanged, sweepChanged, keyOn, keyOff, inPorta, furnaceDac;
     signed char vol, outVol, wave;
     DivMacroInt std;
@@ -46,6 +46,8 @@ class DivPlatformNES: public DivDispatch {
       ins(-1),
       duty(0),
       sweep(8),
+      envMode(3),
+      len(0x1f),
       active(false),
       insChanged(true),
       freqChanged(false),
@@ -74,6 +76,7 @@ class DivPlatformNES: public DivDispatch {
   bool dacAntiClickOn;
   bool useNP;
   bool goingToLoop;
+  bool countMode;
   struct NESAPU* nes;
   xgm::NES_APU* nes1_NP;
   xgm::NES_DMC* nes2_NP;
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 2377e16a..24fc9238 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -206,6 +206,10 @@ const char* cmdName[]={
   "SNES_ECHO_FEEDBACK",
   "SNES_ECHO_FIR",
 
+  "DIV_CMD_NES_ENV_MODE",
+  "DIV_CMD_NES_LENGTH",
+  "DIV_CMD_NES_COUNT_MODE",
+
   "ALWAYS_SET_VOLUME"
 };
 
diff --git a/src/engine/sysDef.cpp b/src/engine/sysDef.cpp
index 8a6c2f69..44b31246 100644
--- a/src/engine/sysDef.cpp
+++ b/src/engine/sysDef.cpp
@@ -693,6 +693,9 @@ void DivEngine::registerSystems() {
       {0x12, {DIV_CMD_STD_NOISE_MODE, "12xx: Set duty cycle/noise mode (pulse: 0 to 3; noise: 0 or 1)"}},
       {0x13, {DIV_CMD_NES_SWEEP, "13xy: Sweep up (x: time; y: shift)",constVal<0>,effectVal}},
       {0x14, {DIV_CMD_NES_SWEEP, "14xy: Sweep down (x: time; y: shift)",constVal<1>,effectVal}},
+      {0x15, {DIV_CMD_NES_ENV_MODE, "15xx: Set envelope mode (0: envelope, 1: length, 2: looping, 3: constant)"}},
+      {0x16, {DIV_CMD_NES_LENGTH, "16xx: Set length counter (refer to manual for a list of values)"}},
+      {0x17, {DIV_CMD_NES_COUNT_MODE, "17xx: Set frame counter mode (0: 4-step, 1: 5-step)"}},
       {0x18, {DIV_CMD_SAMPLE_MODE, "18xx: Select PCM/DPCM mode (0: PCM; 1: DPCM)"}}
     }
   );