diff --git a/README.md b/README.md
index 36b0750..31d2d4f 100644
--- a/README.md
+++ b/README.md
@@ -313,6 +313,20 @@ New features since fork
   - **A bytecode interpreter written in pure go**. It's slightly slower than the
     hand-written assembly code by sointu compiler, but with this, the tracker is
     ultraportable and does not need cgo calls.
+  - **Using Sointu as a sync-tracker**. Similar to [GNU
+    Rocket](https://github.com/yupferris/gnurocket), but (ab)using the tracker
+    we already have for music. We use the Go "rpc" package to send current sync
+    values from the new "sync" opcode + optionally the current fractional row
+    the song is on. The syncs are saved every 256th sample (approximately 172
+    Hz). For 4k intro development, the idea is to write a debug version of the
+    intro that merely loads the shader and listens to the RPC messages, and then
+    draws the shader with those as the uniforms. Then, during the actual 4k
+    intro, one can get sync the data from Sointu: when using syncs,
+    su_render_song takes two buffer parameters, one for sound, another for
+    syncs. These can then be sent to the shader as a uniform float array. A
+    track with two voices, triggering an instrument with a single envelope and a
+    slow filter can even be used as a cheap smooth interpolation mechanism,
+    provided the syncs are added to each other in the shader.
 
 Future goals
 ------------
@@ -327,15 +341,6 @@ Future goals
       bit flag in the existing filter
     - Arbitrary envelopes; for easier automation.
   - **MIDI support for the tracker**.
-  - **Reintroduce the sync mechanism**. 4klang could export the envelopes of all
-    instruments at a 256 times lower frequency, with the purpose of using them
-    as sync data. This feature was removed at some point, but should be
-    reintroduced at some point. Need to investigate the best way to implement
-    this; maybe a "sync" opcode that save the current signal from the stack? Or
-    reusing sends/outs and having special sync output ports, allowing easily
-    combining multiple signals into one sync. Oh, and we probably should dump
-    the whole thing also as a texture to the shader; to fly through the song, in
-    a very literal way.
   - **Find a solution for denormalized signals**. Denormalized floating point
     numbers (floating point numbers that are very very small) can result in 100x
     CPU slow down. We got hit by this already: the damp filters in delay units
@@ -347,16 +352,6 @@ Future goals
 
 Crazy ideas
 -----------
-  - **Using Sointu as a sync-tracker**. Similar to [GNU
-    Rocket](https://github.com/yupferris/gnurocket), but (ab)using the tracker
-    we already have for music. We could define a generic RPC protocol for Sointu
-    tracker send current sync values and time; one could then write a debug
-    version of a 4k intro that merely loads the shader and listens to the RPC
-    messages, and then draws the shader with those as the uniforms. Then, during
-    the actual 4k intro, just render song, get sync data from Sointu and send as
-    uniforms to shader. A track with two voices, triggering an instrument with a
-    single envelope and a slow filter can even be used as a cheap smooth
-    interpolation mechanism.
   - **Hack deeper into audio sources from the OS**. Speech synthesis, I'm eyeing
     at you.
 
diff --git a/cmd/sointu-compile/main.go b/cmd/sointu-compile/main.go
index 817de48..4b801fc 100644
--- a/cmd/sointu-compile/main.go
+++ b/cmd/sointu-compile/main.go
@@ -33,6 +33,7 @@ func main() {
 	list := flag.Bool("l", false, "Do not write files; just list files that would change instead.")
 	stdout := flag.Bool("s", false, "Do not write files; write to standard output instead.")
 	help := flag.Bool("h", false, "Show help.")
+	rowsync := flag.Bool("r", false, "Write the current fractional row as sync #0")
 	library := flag.Bool("a", false, "Compile Sointu into a library. Input files are not needed.")
 	jsonOut := flag.Bool("j", false, "Output the song as .json file instead of compiling.")
 	yamlOut := flag.Bool("y", false, "Output the song as .yml file instead of compiling.")
@@ -53,9 +54,9 @@ func main() {
 	if compile || *library {
 		var err error
 		if *tmplDir != "" {
-			comp, err = compiler.NewFromTemplates(*targetOs, *targetArch, *output16bit, *tmplDir)
+			comp, err = compiler.NewFromTemplates(*targetOs, *targetArch, *output16bit, *rowsync, *tmplDir)
 		} else {
-			comp, err = compiler.New(*targetOs, *targetArch, *output16bit)
+			comp, err = compiler.New(*targetOs, *targetArch, *output16bit, *rowsync)
 		}
 		if err != nil {
 			fmt.Fprintf(os.Stderr, `error creating compiler: %v`, err)
diff --git a/cmd/sointu-nativetrack/main.go b/cmd/sointu-nativetrack/main.go
index 9920acd..78c7223 100644
--- a/cmd/sointu-nativetrack/main.go
+++ b/cmd/sointu-nativetrack/main.go
@@ -17,5 +17,7 @@ func main() {
 	}
 	defer audioContext.Close()
 	synthService := bridge.BridgeService{}
-	gioui.Main(audioContext, synthService)
+	// TODO: native track does not support syncing at the moment (which is why
+	// we pass nil), as the native bridge does not support sync data
+	gioui.Main(audioContext, synthService, nil)
 }
diff --git a/cmd/sointu-play/main.go b/cmd/sointu-play/main.go
index 2a05079..da00820 100644
--- a/cmd/sointu-play/main.go
+++ b/cmd/sointu-play/main.go
@@ -92,7 +92,7 @@ func main() {
 				synth.Release(i)
 			}
 		}
-		buffer, err := sointu.Play(synth, song) // render the song to calculate its length
+		buffer, _, err := sointu.Play(synth, song) // render the song to calculate its length
 		if err != nil {
 			return fmt.Errorf("sointu.Play failed: %v", err)
 		}
diff --git a/cmd/sointu-track/main.go b/cmd/sointu-track/main.go
index ffbfdb0..433f2bf 100644
--- a/cmd/sointu-track/main.go
+++ b/cmd/sointu-track/main.go
@@ -1,21 +1,33 @@
 package main
 
 import (
+	"flag"
 	"fmt"
 	"os"
 
 	"github.com/vsariola/sointu/oto"
+	"github.com/vsariola/sointu/rpc"
 	"github.com/vsariola/sointu/tracker/gioui"
 	"github.com/vsariola/sointu/vm"
 )
 
 func main() {
+	syncAddress := flag.String("address", "", "remote RPC server where to send sync data")
+	flag.Parse()
 	audioContext, err := oto.NewContext()
 	if err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
 	defer audioContext.Close()
+	var syncChannel chan<- []float32
+	if *syncAddress != "" {
+		syncChannel, err = rpc.Sender(*syncAddress)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(1)
+		}
+	}
 	synthService := vm.SynthService{}
-	gioui.Main(audioContext, synthService)
+	gioui.Main(audioContext, synthService, syncChannel)
 }
diff --git a/patch.go b/patch.go
index 5bb901d..5fd14ff 100644
--- a/patch.go
+++ b/patch.go
@@ -37,6 +37,18 @@ func (p Patch) NumDelayLines() int {
 	return total
 }
 
+func (p Patch) NumSyncs() int {
+	total := 0
+	for _, instr := range p {
+		for _, unit := range instr.Units {
+			if unit.Type == "sync" {
+				total += instr.NumVoices
+			}
+		}
+	}
+	return total
+}
+
 func (p Patch) FirstVoiceForInstrument(instrIndex int) int {
 	ret := 0
 	for _, t := range p[:instrIndex] {
diff --git a/rpc/rpc.go b/rpc/rpc.go
new file mode 100644
index 0000000..a6dad65
--- /dev/null
+++ b/rpc/rpc.go
@@ -0,0 +1,57 @@
+package rpc
+
+import (
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"net/rpc"
+)
+
+type SyncServer struct {
+	channel chan []float32
+}
+
+func (s *SyncServer) Sync(syncData []float32, reply *int) error {
+	select {
+	case s.channel <- syncData:
+	default:
+	}
+	return nil
+}
+
+func Receiver() (<-chan []float32, error) {
+	c := make(chan []float32, 1)
+	server := &SyncServer{channel: c}
+	rpc.Register(server)
+	rpc.HandleHTTP()
+	l, e := net.Listen("tcp", ":31337")
+	if e != nil {
+		log.Fatal("listen error:", e)
+		return nil, fmt.Errorf("net.listen failed: %v", e)
+	}
+	go func() {
+		defer close(c)
+		http.Serve(l, nil)
+	}()
+	return c, nil
+}
+
+func Sender(serverAddress string) (chan<- []float32, error) {
+	c := make(chan []float32, 256)
+	client, err := rpc.DialHTTP("tcp", serverAddress+":31337")
+	if err != nil {
+		log.Fatal("dialing:", err)
+		return nil, fmt.Errorf("rpc.DialHTTP failed: %v", err)
+	}
+	go func() {
+		for msg := range c {
+			var reply int
+			err = client.Call("SyncServer.Sync", msg, &reply)
+			if err != nil {
+				log.Fatal("SyncServer.Sync error:", err)
+			}
+		}
+	}()
+	return c, nil
+}
diff --git a/rpc/rpc_test.go b/rpc/rpc_test.go
new file mode 100644
index 0000000..44918f6
--- /dev/null
+++ b/rpc/rpc_test.go
@@ -0,0 +1,24 @@
+package rpc_test
+
+import (
+	"testing"
+
+	"github.com/vsariola/sointu/rpc"
+)
+
+func TestSendReceive(t *testing.T) {
+	receiver, err := rpc.Receiver()
+	if err != nil {
+		t.Fatalf("rpc.Receiver error: %v", err)
+	}
+	sender, err := rpc.Sender("127.0.0.1")
+	if err != nil {
+		t.Fatalf("rpc.Sender error: %v", err)
+	}
+	value := []float32{42}
+	sender <- value
+	valueGot := <-receiver
+	if valueGot[0] != value[0] {
+		t.Fatalf("rpc.Sender error: %v", err)
+	}
+}
diff --git a/synth.go b/synth.go
index 219993b..3093805 100644
--- a/synth.go
+++ b/synth.go
@@ -7,7 +7,7 @@ import (
 )
 
 type Synth interface {
-	Render(buffer []float32, maxtime int) (int, int, error)
+	Render(buffer []float32, syncBuffer []float32, maxtime int) (sample int, syncs int, time int, err error)
 	Update(patch Patch) error
 	Trigger(voice int, note byte)
 	Release(voice int)
@@ -18,7 +18,7 @@ type SynthService interface {
 }
 
 func Render(synth Synth, buffer []float32) error {
-	s, _, err := synth.Render(buffer, math.MaxInt32)
+	s, _, _, err := synth.Render(buffer, nil, math.MaxInt32)
 	if err != nil {
 		return fmt.Errorf("sointu.Render failed: %v", err)
 	}
@@ -28,10 +28,10 @@ func Render(synth Synth, buffer []float32) error {
 	return nil
 }
 
-func Play(synth Synth, song Song) ([]float32, error) {
+func Play(synth Synth, song Song) ([]float32, []float32, error) {
 	err := song.Validate()
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 	curVoices := make([]int, len(song.Score.Tracks))
 	for i := range curVoices {
@@ -39,7 +39,10 @@ func Play(synth Synth, song Song) ([]float32, error) {
 	}
 	initialCapacity := song.Score.LengthInRows() * song.SamplesPerRow() * 2
 	buffer := make([]float32, 0, initialCapacity)
+	syncBuffer := make([]float32, 0, initialCapacity)
 	rowbuffer := make([]float32, song.SamplesPerRow()*2)
+	numSyncs := song.Patch.NumSyncs()
+	syncRowBuffer := make([]float32, ((song.SamplesPerRow()+255)/256)*(1+numSyncs))
 	for row := 0; row < song.Score.LengthInRows(); row++ {
 		patternRow := row % song.Score.RowsPerPattern
 		pattern := row / song.Score.RowsPerPattern
@@ -73,16 +76,22 @@ func Play(synth Synth, song Song) ([]float32, error) {
 		}
 		tries := 0
 		for rowtime := 0; rowtime < song.SamplesPerRow(); {
-			samples, time, err := synth.Render(rowbuffer, song.SamplesPerRow()-rowtime)
+			samples, syncs, time, err := synth.Render(rowbuffer, syncRowBuffer, song.SamplesPerRow()-rowtime)
+			for i := 0; i < syncs; i++ {
+				t := syncRowBuffer[i*(1+numSyncs)]
+				t = (t+float32(rowtime))/(float32(song.SamplesPerRow())) + float32(row)
+				syncRowBuffer[i*(1+numSyncs)] = t
+			}
 			if err != nil {
-				return buffer, fmt.Errorf("render failed: %v", err)
+				return buffer, syncBuffer, fmt.Errorf("render failed: %v", err)
 			}
 			rowtime += time
 			buffer = append(buffer, rowbuffer[:samples*2]...)
+			syncBuffer = append(syncBuffer, syncRowBuffer[:syncs]...)
 			if tries > 100 {
-				return nil, fmt.Errorf("Song speed modulation likely so slow that row never advances; error at pattern %v, row %v", pattern, patternRow)
+				return nil, nil, fmt.Errorf("Song speed modulation likely so slow that row never advances; error at pattern %v, row %v", pattern, patternRow)
 			}
 		}
 	}
-	return buffer, nil
+	return buffer, syncBuffer, nil
 }
diff --git a/templates/amd64-386/flowcontrol.asm b/templates/amd64-386/flowcontrol.asm
index 12c4980..6e34e66 100644
--- a/templates/amd64-386/flowcontrol.asm
+++ b/templates/amd64-386/flowcontrol.asm
@@ -21,3 +21,24 @@
     fstp    dword [{{.WRK}}] ; save the remainder for future
     ret
 {{end}}
+
+
+{{- if or .RowSync (.HasOp "sync")}}
+;-------------------------------------------------------------------------------
+;   SYNC opcode: save the stack top to sync buffer
+;-------------------------------------------------------------------------------
+{{.Func "su_op_sync" "Opcode"}}
+{{- if not .Library}}
+    ; TODO: syncs are NOPs when compiling as library, should figure out a way to
+    ; make them work when compiling to use the native track also
+    mov     {{.AX}}, [{{.Stack "GlobalTick"}}]
+    test    al, al
+    jne     su_op_sync_skip
+    xchg    {{.AX}}, [{{.Stack "SyncBufPtr"}}]
+    fst     dword [{{.AX}}]
+    add     {{.AX}}, 4
+    xchg    {{.AX}}, [{{.Stack "SyncBufPtr"}}]
+su_op_sync_skip:
+{{- end}}
+    ret
+{{end}}
diff --git a/templates/amd64-386/patch.asm b/templates/amd64-386/patch.asm
index edcc490..a287292 100644
--- a/templates/amd64-386/patch.asm
+++ b/templates/amd64-386/patch.asm
@@ -14,6 +14,14 @@
 ;-------------------------------------------------------------------------------
 {{.Func "su_run_vm"}}
     {{- .PushRegs .CX "DelayWorkSpace" .DX "Synth" .COM "CommandStream" .WRK "Voice" .VAL "ValueStream" | indent 4}}
+    {{- if .RowSync}}
+    fild    dword [{{.Stack "Sample"}}]
+    {{.Int .Song.SamplesPerRow | .Prepare | indent 8}}
+    fidiv   dword [{{.Int .Song.SamplesPerRow | .Use}}]
+    fiadd   dword [{{.Stack "Row"}}]
+    {{.Call "su_op_sync"}}
+    fstp    st0
+    {{- end}}
 su_run_vm_loop:                                     ; loop until all voices done
     movzx   edi, byte [{{.COM}}]                         ; edi = command byte
     inc     {{.COM}}                                     ; move to next instruction
diff --git a/templates/amd64-386/player.asm b/templates/amd64-386/player.asm
index de73750..27442b0 100644
--- a/templates/amd64-386/player.asm
+++ b/templates/amd64-386/player.asm
@@ -14,12 +14,22 @@ su_synth_obj:
 ;   the output buffer. Renders the compile time hard-coded song to the buffer.
 ;   Stack:  output_ptr
 ;-------------------------------------------------------------------------------
+{{- if or .RowSync (.HasOp "sync")}}
+{{.ExportFunc "su_render_song" "OutputBufPtr" "SyncBufPtr"}}
+{{- else}}
 {{.ExportFunc "su_render_song" "OutputBufPtr"}}
+{{- end}}
     {{-  if .Amd64}}
     {{- if eq .OS "windows"}}
     {{- .PushRegs "rcx" "OutputBufPtr" "rdi" "NonVolatileRsi" "rsi" "NonVolatile" "rbx" "NonVolatileRbx" "rbp" "NonVolatileRbp" | indent 4}} ; rcx = ptr to buf. rdi,rsi,rbx,rbp  nonvolatile
+    {{- if or .RowSync (.HasOp "sync")}}
+    {{- .PushRegs "rdx" "SyncBufPtr" | indent 4}}
+    {{- end}}
     {{- else}} ; SystemV amd64 ABI, linux mac or hopefully something similar
     {{- .PushRegs "rdi" "OutputBufPtr" "rbx" "NonVolatileRbx" "rbp" "NonVolatileRbp" | indent 4}}
+    {{- if or .RowSync (.HasOp "sync")}}
+    {{- .PushRegs "rsi" "SyncBufPtr" | indent 4}}
+    {{- end}}
     {{- end}}
     {{- else}}
     {{- .PushRegs | indent 4}}
@@ -68,6 +78,9 @@ su_render_sampleloop:                   ; loop through every sample in the row
     {{$.Pop $.AX}}
     {{- end}}
     {{-  if .Amd64}}
+    {{- if or .RowSync (.HasOp "sync")}}
+    {{.Pop .AX}} ; pop the sync buf ptr away
+    {{- end}}
     {{- if eq .OS "windows"}}
     ; Windows64 ABI, rdi rsi rbx rbp non-volatile
     {{- .PopRegs "rcx" "rdi" "rsi" "rbx" "rbp" | indent 4}}
@@ -78,8 +91,12 @@ su_render_sampleloop:                   ; loop through every sample in the row
     ret
     {{- else}}
     {{- .PopRegs | indent 4}}
+    {{- if or .RowSync (.HasOp "sync")}}
+    ret     8
+    {{- else}}
     ret     4
     {{- end}}
+    {{- end}}
 
 ;-------------------------------------------------------------------------------
 ;   su_update_voices function: polyphonic & chord implementation
diff --git a/templates/amd64-386/player.h b/templates/amd64-386/player.h
index 23e23a5..a78431a 100644
--- a/templates/amd64-386/player.h
+++ b/templates/amd64-386/player.h
@@ -13,6 +13,15 @@
 #define SU_LENGTH_IN_ROWS       (SU_LENGTH_IN_PATTERNS*SU_PATTERN_SIZE)
 #define SU_SAMPLES_PER_ROW      (SU_SAMPLE_RATE*60/(SU_BPM*SU_ROWS_PER_BEAT))
 
+{{- if or .RowSync (.HasOp "sync")}}
+{{- if .RowSync}}
+#define SU_NUMSYNCS             {{add1 .Song.Patch.NumSyncs}}
+{{- else}}
+#define SU_NUMSYNCS             {{.Song.Patch.NumSyncs}}
+{{- end}}
+#define SU_SYNCBUFFER_LENGTH    ((SU_LENGTH_IN_SAMPLES+255)>>8)*SU_NUMSYNCS
+{{- end}}
+
 #include <stdint.h>
 #if UINTPTR_MAX == 0xffffffff
     #if defined(__clang__) || defined(__GNUC__)
@@ -39,7 +48,12 @@ typedef float SUsample;
 extern "C" {
 #endif
 
+{{- if or .RowSync (.HasOp "sync")}}
+void SU_CALLCONV su_render_song(SUsample *buffer,float *syncBuffer);
+#define SU_SYNC
+{{- else}}
 void SU_CALLCONV su_render_song(SUsample *buffer);
+{{- end}}
 {{- if gt (.SampleOffsets | len) 0}}
 void SU_CALLCONV su_load_gmdls();
 #define SU_LOAD_GMDLS
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 6617c50..eb0adea 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -1,10 +1,13 @@
 function(regression_test testname)
 
-    if(${ARGC} LESS 6)
-        if(${ARGC} LESS 4)
+    if(ARGV5)
+        set(source ${ARGV5})
+        add_executable(${testname} ${source} test_renderer.c)
+    else()
+        if(ARGV3)
+            set(source ${ARGV3}.yml)            
+        else()           
             set(source ${testname}.yml)
-        else()
-            set(source ${ARGV3}.yml)
         endif()
 
         set(asmfile ${testname}.asm)
@@ -19,7 +22,7 @@ function(regression_test testname)
         add_executable(${testname} test_renderer.c ${asmfile})
         target_compile_definitions(${testname} PUBLIC TEST_HEADER=<${testname}.h>)
 
-        if (NODE AND WAT2WASM AND NOT ${testname} MATCHES "sample")
+        if (NODE AND WAT2WASM AND NOT ${testname} MATCHES "sample" AND NOT ${testname} MATCHES "sync")
             set(wasmfile ${CMAKE_CURRENT_BINARY_DIR}/${testname}.wasm)
             set(watfile ${CMAKE_CURRENT_BINARY_DIR}/${testname}.wat)
             set(wasmtarget wasm_${testname})
@@ -29,31 +32,29 @@ function(regression_test testname)
                 DEPENDS sointu-compiler
             )
             add_test(${wasmtarget} ${NODE} ${CMAKE_CURRENT_SOURCE_DIR}/wasm_test_renderer.es6 ${wasmfile} ${CMAKE_CURRENT_SOURCE_DIR}/expected_output/${testname}.raw)
-        endif()
-    else()
-        set(source ${ARGV5})
-        add_executable(${testname} ${source} test_renderer.c)
+        endif()    
     endif()
 
-    add_test(${testname} ${testname} ${CMAKE_CURRENT_SOURCE_DIR}/expected_output/${testname}.raw)
+    if (${testname} MATCHES "sync")
+        add_test(${testname} ${testname} ${CMAKE_CURRENT_SOURCE_DIR}/expected_output/${testname}.raw ${CMAKE_CURRENT_SOURCE_DIR}/expected_output/${testname}_syncbuf.raw)
+    else()
+        add_test(${testname} ${testname} ${CMAKE_CURRENT_SOURCE_DIR}/expected_output/${testname}.raw)
+    endif()
     target_link_libraries(${testname} ${HEADERLIB})
 
     target_include_directories(${testname} PUBLIC ${CMAKE_CURRENT_BINARY_DIR})
     target_compile_definitions(${testname} PUBLIC TEST_NAME="${testname}")
-
-    if(ARGC GREATER 1)
-        if (ARGV1)
-            message("${testname} requires ${ARGV1}")
-            set_tests_properties(${testname} PROPERTIES FIXTURES_REQUIRED "${ARGV1}")
-        endif()
+    
+    if (ARGV1)
+        message("${testname} requires ${ARGV1}")
+        set_tests_properties(${testname} PROPERTIES FIXTURES_REQUIRED "${ARGV1}")
+    endif()
+  
+    if (ARGV2)
+        message("${testname} setups ${ARGV2}")
+        set_tests_properties(${testname} PROPERTIES FIXTURES_SETUP "${ARGV2}")
     endif()
 
-    if(ARGC GREATER 2)
-        if (ARGV2)
-            message("${testname} setups ${ARGV2}")
-            set_tests_properties(${testname} PROPERTIES FIXTURES_SETUP "${ARGV2}")
-        endif()
-    endif()
 endfunction(regression_test)
 
 regression_test(test_envelope "" ENVELOPE)
@@ -157,6 +158,7 @@ regression_test(test_envelope_16bit ENVELOPE "" test_envelope "-i")
 regression_test(test_polyphony "ENVELOPE;VCO_SINE")
 regression_test(test_chords "ENVELOPE;VCO_SINE")
 regression_test(test_speed "ENVELOPE;VCO_SINE")
+regression_test(test_sync "ENVELOPE" "" "" "-r")
 
 regression_test(test_render_samples ENVELOPE "" "" "" test_render_samples.c)
 target_link_libraries(test_render_samples ${STATICLIB})
diff --git a/tests/expected_output/test_sync.raw b/tests/expected_output/test_sync.raw
new file mode 100644
index 0000000..5b81d2f
Binary files /dev/null and b/tests/expected_output/test_sync.raw differ
diff --git a/tests/expected_output/test_sync_syncbuf.raw b/tests/expected_output/test_sync_syncbuf.raw
new file mode 100644
index 0000000..d7e9033
Binary files /dev/null and b/tests/expected_output/test_sync_syncbuf.raw differ
diff --git a/tests/test_renderer.c b/tests/test_renderer.c
index 997cc5b..40fe45e 100644
--- a/tests/test_renderer.c
+++ b/tests/test_renderer.c
@@ -16,6 +16,11 @@
 #include TEST_HEADER
 SUsample buf[SU_BUFFER_LENGTH];
 SUsample filebuf[SU_BUFFER_LENGTH];
+#ifdef SU_SYNC
+float syncBuf[SU_SYNCBUFFER_LENGTH];
+float fileSyncBuf[SU_BUFFER_LENGTH];
+#endif
+
 
 int main(int argc, char* argv[]) {
     FILE* f;
@@ -36,7 +41,11 @@ int main(int argc, char* argv[]) {
     su_load_gmdls();
     #endif
 
+    #ifdef SU_SYNC
+    su_render_song(buf, syncBuf);
+    #else
     su_render_song(buf);
+    #endif
 
 #if defined (_WIN32)
     CreateDirectory(actual_output_folder, NULL);
@@ -49,6 +58,13 @@ int main(int argc, char* argv[]) {
     fwrite((void*)buf, sizeof(SUsample), SU_BUFFER_LENGTH, f);
     fclose(f);
 
+    #ifdef SU_SYNC
+    snprintf(filename, sizeof filename, "%s%s%s", actual_output_folder, test_name, "_syncbuf.raw");
+    f = fopen(filename, "wb");
+    fwrite((void*)syncBuf, sizeof(float), SU_SYNCBUFFER_LENGTH, f);
+    fclose(f);
+    #endif
+
     f = fopen(argv[1], "rb");
 
     if (f == NULL) {
@@ -92,6 +108,42 @@ int main(int argc, char* argv[]) {
         printf("Warning: Sointu rendered almost correct wave, but a small maximum error of %f\n",max_diff);        
     }
 
+#ifdef SU_SYNC
+    f = fopen(argv[2], "rb");
+
+    if (f == NULL) {
+        printf("No expected sync waveform found!\n");
+        goto fail;
+    }
+
+    fseek(f, 0, SEEK_END);
+    fsize = ftell(f);
+    fseek(f, 0, SEEK_SET);
+
+    if (SU_SYNCBUFFER_LENGTH * sizeof(float) < fsize) {
+        printf("Sointu rendered shorter sync wave than expected\n");
+        goto fail;
+    }
+
+    if (SU_SYNCBUFFER_LENGTH * sizeof(float) > fsize) {
+        printf("Sointu rendered longer sync wave than expected\n");
+        goto fail;
+    }
+
+    fread((void*)fileSyncBuf, fsize, 1, f);
+    fclose(f);
+    f = NULL;
+
+    max_diff = 0.0f;
+
+    for (n = 0; n < SU_SYNCBUFFER_LENGTH; n++) {
+        diff = (float)fabs(syncBuf[n] - fileSyncBuf[n]);
+        if (diff > 1e-3f || isnan(diff)) {
+            printf("Sointu rendered different sync wave than expected\n");
+            goto fail;
+        }
+    }
+#endif
     return 0;
 
 fail:
diff --git a/tests/test_sync.yml b/tests/test_sync.yml
new file mode 100644
index 0000000..92da414
--- /dev/null
+++ b/tests/test_sync.yml
@@ -0,0 +1,20 @@
+bpm: 100
+rowsperbeat: 4
+score:
+    rowsperpattern: 16
+    length: 2
+    tracks:
+        - numvoices: 1
+          order: [0, 0]
+          patterns: [[64, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0]]
+patch:
+    - numvoices: 1
+      units:
+        - type: envelope
+          parameters: {attack: 64, decay: 64, gain: 128, release: 80, stereo: 0, sustain: 64}
+        - type: sync
+        - type: envelope
+          parameters: {attack: 95, decay: 64, gain: 128, release: 80, stereo: 0, sustain: 64}
+        - type: sync
+        - type: out
+          parameters: {gain: 128, stereo: 1}
diff --git a/tracker/defaultsong.go b/tracker/defaultsong.go
index 1ea0ef7..eec10b1 100644
--- a/tracker/defaultsong.go
+++ b/tracker/defaultsong.go
@@ -40,6 +40,7 @@ var defaultUnits = map[string]sointu.Unit{
 	"speed":      {Type: "speed", Parameters: map[string]int{}},
 	"compressor": {Type: "compressor", Parameters: map[string]int{"stereo": 0, "attack": 64, "release": 64, "invgain": 64, "threshold": 64, "ratio": 64}},
 	"send":       {Type: "send", Parameters: map[string]int{"stereo": 0, "amount": 128, "voice": 0, "unit": 0, "port": 0, "sendpop": 1}},
+	"sync":       {Type: "sync", Parameters: map[string]int{}},
 }
 
 var defaultInstrument = sointu.Instrument{
diff --git a/tracker/gioui/run.go b/tracker/gioui/run.go
index 0c05990..c6b8caa 100644
--- a/tracker/gioui/run.go
+++ b/tracker/gioui/run.go
@@ -51,13 +51,13 @@ func (t *Tracker) Run(w *app.Window) error {
 	}
 }
 
-func Main(audioContext sointu.AudioContext, synthService sointu.SynthService) {
+func Main(audioContext sointu.AudioContext, synthService sointu.SynthService, syncChannel chan<- []float32) {
 	go func() {
 		w := app.NewWindow(
 			app.Size(unit.Dp(800), unit.Dp(600)),
 			app.Title("Sointu Tracker"),
 		)
-		t := New(audioContext, synthService)
+		t := New(audioContext, synthService, syncChannel)
 		defer t.Close()
 		if err := t.Run(w); err != nil {
 			fmt.Println(err)
diff --git a/tracker/gioui/tracker.go b/tracker/gioui/tracker.go
index be9d967..4bc7b80 100644
--- a/tracker/gioui/tracker.go
+++ b/tracker/gioui/tracker.go
@@ -99,7 +99,7 @@ func (t *Tracker) Close() {
 	t.audioContext.Close()
 }
 
-func New(audioContext sointu.AudioContext, synthService sointu.SynthService) *Tracker {
+func New(audioContext sointu.AudioContext, synthService sointu.SynthService, syncChannel chan<- []float32) *Tracker {
 	t := &Tracker{
 		Theme:                 material.NewTheme(gofont.Collection()),
 		audioContext:          audioContext,
@@ -160,7 +160,7 @@ func New(audioContext sointu.AudioContext, synthService sointu.SynthService) *Tr
 	sprObserver := make(chan int, 16)
 	t.AddSamplesPerRowObserver(sprObserver)
 	audioChannel := make(chan []float32)
-	t.player = tracker.NewPlayer(synthService, t.playerCloser, patchObserver, scoreObserver, sprObserver, t.refresh, audioChannel, vuBufferObserver)
+	t.player = tracker.NewPlayer(synthService, t.playerCloser, patchObserver, scoreObserver, sprObserver, t.refresh, syncChannel, audioChannel, vuBufferObserver)
 	audioOut := audioContext.Output()
 	go func() {
 		for buf := range audioChannel {
diff --git a/tracker/player.go b/tracker/player.go
index ddec090..192b1a2 100644
--- a/tracker/player.go
+++ b/tracker/player.go
@@ -66,13 +66,16 @@ func (p *Player) Enabled() bool {
 	return atomic.LoadInt32(&p.synthNotNil) == 1
 }
 
-func NewPlayer(service sointu.SynthService, closer <-chan struct{}, patchs <-chan sointu.Patch, scores <-chan sointu.Score, samplesPerRows <-chan int, posChanged chan<- struct{}, outputs ...chan<- []float32) *Player {
+func NewPlayer(service sointu.SynthService, closer <-chan struct{}, patchs <-chan sointu.Patch, scores <-chan sointu.Score, samplesPerRows <-chan int, posChanged chan<- struct{}, syncOutput chan<- []float32, outputs ...chan<- []float32) *Player {
 	p := &Player{playCmds: make(chan uint64, 16)}
 	go func() {
 		var score sointu.Score
 		buffer := make([]float32, 2048)
 		buffer2 := make([]float32, 2048)
 		zeros := make([]float32, 2048)
+		totalSyncs := 1 // just the beat
+		syncBuffer := make([]float32, (2048+255)/256*totalSyncs)
+		syncBuffer2 := make([]float32, (2048+255)/256*totalSyncs)
 		rowTime := 0
 		samplesPerRow := math.MaxInt32
 		var trackIDs []uint32
@@ -103,6 +106,9 @@ func NewPlayer(service sointu.SynthService, closer <-chan struct{}, patchs <-cha
 						}
 					}
 				}
+				totalSyncs = 1 + p.patch.NumSyncs()
+				syncBuffer = make([]float32, ((2048+255)/256)*totalSyncs)
+				syncBuffer2 = make([]float32, ((2048+255)/256)*totalSyncs)
 				p.mutex.Unlock()
 			case score = <-scores:
 				if row, playing := p.Position(); playing {
@@ -165,17 +171,29 @@ func NewPlayer(service sointu.SynthService, closer <-chan struct{}, patchs <-cha
 						renderTime = math.MaxInt32
 					}
 					p.mutex.Lock()
-					rendered, timeAdvanced, err := p.synth.Render(buffer, renderTime)
+					rendered, syncs, timeAdvanced, err := p.synth.Render(buffer, syncBuffer, renderTime)
 					if err != nil {
 						p.synth = nil
 						atomic.StoreInt32(&p.synthNotNil, 0)
 					}
 					p.mutex.Unlock()
+					for i := 0; i < syncs; i++ {
+						a := syncBuffer[i*totalSyncs]
+						b := (a+float32(rowTime))/float32(samplesPerRow) + float32(row.Pattern*score.RowsPerPattern+row.Row)
+						syncBuffer[i*totalSyncs] = b
+					}
 					rowTime += timeAdvanced
+					for window := syncBuffer[:totalSyncs*syncs]; len(window) > 0; window = window[totalSyncs:] {
+						select {
+						case syncOutput <- window[:totalSyncs]:
+						default:
+						}
+					}
 					for _, o := range outputs {
 						o <- buffer[:rendered*2]
 					}
 					buffer2, buffer = buffer, buffer2
+					syncBuffer2, syncBuffer = syncBuffer, syncBuffer2
 				} else {
 					rowTime += len(zeros) / 2
 					for _, o := range outputs {
diff --git a/unittype.go b/unittype.go
index 818e322..424f11a 100644
--- a/unittype.go
+++ b/unittype.go
@@ -131,6 +131,7 @@ var UnitTypes = map[string]([]UnitParameter){
 	"in": []UnitParameter{
 		{Name: "stereo", MinValue: 0, MaxValue: 1, CanSet: true, CanModulate: false},
 		{Name: "channel", MinValue: 0, MaxValue: 6, CanSet: true, CanModulate: false}},
+	"sync": []UnitParameter{},
 }
 
 var Ports = make(map[string]([]string))
diff --git a/vm/compiler/bridge/bridge.go b/vm/compiler/bridge/bridge.go
index 71da140..fb77d5e 100644
--- a/vm/compiler/bridge/bridge.go
+++ b/vm/compiler/bridge/bridge.go
@@ -70,17 +70,18 @@ func Synth(patch sointu.Patch) (*C.Synth, error) {
 // time > maxtime, as it is modulated and the time could advance by 2 or more, so the loop
 // exit condition would fire when the time is already past maxtime.
 // Under no conditions, nsamples >= len(buffer)/2 i.e. guaranteed to never overwrite the buffer.
-func (synth *C.Synth) Render(buffer []float32, maxtime int) (int, int, error) {
+func (synth *C.Synth) Render(buffer []float32, syncBuffer []float32, maxtime int) (int, int, int, error) {
+	// TODO: syncBuffer is not getting passed to cgo; do we want to even try to support the syncing with the native bridge
 	if len(buffer)%1 == 1 {
-		return -1, -1, errors.New("RenderTime writes stereo signals, so buffer should have even length")
+		return -1, -1, -1, errors.New("RenderTime writes stereo signals, so buffer should have even length")
 	}
 	samples := C.int(len(buffer) / 2)
 	time := C.int(maxtime)
 	errcode := int(C.su_render(synth, (*C.float)(&buffer[0]), &samples, &time))
 	if errcode > 0 {
-		return int(samples), int(time), &RenderError{errcode: errcode}
+		return int(samples), 0, int(time), &RenderError{errcode: errcode}
 	}
-	return int(samples), int(time), nil
+	return int(samples), 0, int(time), nil
 }
 
 // Trigger is part of C.Synths' implementation of sointu.Synth interface
diff --git a/vm/compiler/bridge/bridge_test.go b/vm/compiler/bridge/bridge_test.go
index c4627b1..af01ddc 100644
--- a/vm/compiler/bridge/bridge_test.go
+++ b/vm/compiler/bridge/bridge_test.go
@@ -44,7 +44,7 @@ func TestOscillatSine(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Compiling patch failed: %v", err)
 	}
-	buffer, err := sointu.Play(synth, song)
+	buffer, _, err := sointu.Play(synth, song)
 	if err != nil {
 		t.Fatalf("Render failed: %v", err)
 	}
@@ -103,7 +103,7 @@ func TestAllRegressionTests(t *testing.T) {
 			if err != nil {
 				t.Fatalf("Compiling patch failed: %v", err)
 			}
-			buffer, err := sointu.Play(synth, song)
+			buffer, _, err := sointu.Play(synth, song)
 			buffer = buffer[:song.Score.LengthInRows()*song.SamplesPerRow()*2] // extend to the nominal length always.
 			if err != nil {
 				t.Fatalf("Play failed: %v", err)
diff --git a/vm/compiler/compiler.go b/vm/compiler/compiler.go
index f102061..8049c41 100644
--- a/vm/compiler/compiler.go
+++ b/vm/compiler/compiler.go
@@ -18,10 +18,11 @@ type Compiler struct {
 	OS          string
 	Arch        string
 	Output16Bit bool
+	RowSync     bool
 }
 
 // New returns a new compiler using the default .asm templates
-func New(os string, arch string, output16Bit bool) (*Compiler, error) {
+func New(os string, arch string, output16Bit bool, rowsync bool) (*Compiler, error) {
 	_, myname, _, _ := runtime.Caller(0)
 	var subdir string
 	if arch == "386" || arch == "amd64" {
@@ -32,17 +33,17 @@ func New(os string, arch string, output16Bit bool) (*Compiler, error) {
 		return nil, fmt.Errorf("compiler.New failed, because only amd64, 386 and wasm archs are supported (targeted architecture was %v)", arch)
 	}
 	templateDir := filepath.Join(path.Dir(myname), "..", "..", "templates", subdir)
-	compiler, err := NewFromTemplates(os, arch, output16Bit, templateDir)
+	compiler, err := NewFromTemplates(os, arch, output16Bit, rowsync, templateDir)
 	return compiler, err
 }
 
-func NewFromTemplates(os string, arch string, output16Bit bool, templateDirectory string) (*Compiler, error) {
+func NewFromTemplates(os string, arch string, output16Bit bool, rowsync bool, templateDirectory string) (*Compiler, error) {
 	globPtrn := filepath.Join(templateDirectory, "*.*")
 	tmpl, err := template.New("base").Funcs(sprig.TxtFuncMap()).ParseGlob(globPtrn)
 	if err != nil {
 		return nil, fmt.Errorf(`could not create template based on directory "%v": %v`, templateDirectory, err)
 	}
-	return &Compiler{Template: tmpl, OS: os, Arch: arch, Output16Bit: output16Bit}, nil
+	return &Compiler{Template: tmpl, OS: os, Arch: arch, RowSync: rowsync, Output16Bit: output16Bit}, nil
 }
 
 func (com *Compiler) Library() (map[string]string, error) {
diff --git a/vm/compiler/x86_macros.go b/vm/compiler/x86_macros.go
index 88f0656..4175710 100644
--- a/vm/compiler/x86_macros.go
+++ b/vm/compiler/x86_macros.go
@@ -354,15 +354,25 @@ func (p *X86Macros) FmtStack() string {
 }
 
 func (p *X86Macros) ExportFunc(name string, params ...string) string {
-	if !p.Amd64 {
-		reverseParams := make([]string, len(params))
-		for i, param := range params {
-			reverseParams[len(params)-1-i] = param
-		}
-		p.Stacklocs = append(reverseParams, "retaddr_"+name) // in 32-bit, we use stdcall and parameters are in the stack
-		if p.OS == "windows" {
-			return fmt.Sprintf("%[1]v\nglobal _%[2]v@%[3]v\n_%[2]v@%[3]v:", p.SectText(name), name, len(params)*4)
-		}
+	numRegisters := 0 // in 32-bit systems, we use stdcall: everything in stack
+	switch {
+	case p.Amd64 && p.OS == "windows":
+		numRegisters = 4 // 64-bit windows has 4 parameters in registers, rest in stack
+	case p.Amd64:
+		numRegisters = 6 // System V ABI has 6 parameters in registers, rest in stack
+	}
+	if len(params) > numRegisters {
+		params = params[numRegisters:]
+	} else {
+		params = nil
+	}
+	reverseParams := make([]string, len(params))
+	for i, param := range params {
+		reverseParams[len(params)-1-i] = param
+	}
+	p.Stacklocs = append(reverseParams, "retaddr_"+name) // in 32-bit, we use stdcall and parameters are in the stack
+	if !p.Amd64 && p.OS == "windows" {
+		return fmt.Sprintf("%[1]v\nglobal _%[2]v@%[3]v\n_%[2]v@%[3]v:", p.SectText(name), name, len(params)*4)
 	}
 	if p.OS == "darwin" {
 		return fmt.Sprintf("%[1]v\nglobal _%[2]v\n_%[2]v:", p.SectText(name), name)
diff --git a/vm/interpreter.go b/vm/interpreter.go
index 3751ea5..a81285e 100644
--- a/vm/interpreter.go
+++ b/vm/interpreter.go
@@ -115,7 +115,7 @@ func (s *Interpreter) Update(patch sointu.Patch) error {
 	return nil
 }
 
-func (s *Interpreter) Render(buffer []float32, maxtime int) (samples int, time int, renderError error) {
+func (s *Interpreter) Render(buffer []float32, syncBuf []float32, maxtime int) (samples int, syncs int, time int, renderError error) {
 	defer func() {
 		if err := recover(); err != nil {
 			renderError = fmt.Errorf("render panicced: %v", err)
@@ -133,6 +133,10 @@ func (s *Interpreter) Render(buffer []float32, maxtime int) (samples int, time i
 		voicesRemaining := s.bytePatch.NumVoices
 		voices := s.synth.voices[:]
 		units := voices[0].units[:]
+		if byte(s.synth.globalTime) == 0 { // every 256 samples
+			syncBuf[0], syncBuf = float32(time), syncBuf[1:]
+			syncs++
+		}
 		for voicesRemaining > 0 {
 			op := commands[0]
 			commands = commands[1:]
@@ -152,7 +156,7 @@ func (s *Interpreter) Render(buffer []float32, maxtime int) (samples int, time i
 			}
 			tcount := transformCounts[opNoStereo-1]
 			if len(values) < tcount {
-				return samples, time, errors.New("value stream ended prematurely")
+				return samples, syncs, time, errors.New("value stream ended prematurely")
 			}
 			voice := &voices[0]
 			unit := &units[0]
@@ -523,16 +527,20 @@ func (s *Interpreter) Render(buffer []float32, maxtime int) (samples int, time i
 				if stereo {
 					stack = append(stack, gain)
 				}
+			case opSync:
+				if byte(s.synth.globalTime) == 0 { // every 256 samples
+					syncBuf[0], syncBuf = float32(stack[l-1]), syncBuf[1:]
+				}
 			default:
-				return samples, time, errors.New("invalid / unimplemented opcode")
+				return samples, syncs, time, errors.New("invalid / unimplemented opcode")
 			}
 			units = units[1:]
 		}
 		if len(stack) < 4 {
-			return samples, time, errors.New("stack underflow")
+			return samples, syncs, time, errors.New("stack underflow")
 		}
 		if len(stack) > 4 {
-			return samples, time, errors.New("stack not empty")
+			return samples, syncs, time, errors.New("stack not empty")
 		}
 		buffer[0] = synth.outputs[0]
 		buffer[1] = synth.outputs[1]
@@ -544,7 +552,7 @@ func (s *Interpreter) Render(buffer []float32, maxtime int) (samples int, time i
 		s.synth.globalTime++
 	}
 	s.stack = stack[:0]
-	return samples, time, nil
+	return samples, syncs, time, nil
 }
 
 func (s *synth) rand() float32 {
diff --git a/vm/interpreter_test.go b/vm/interpreter_test.go
index 20b97a0..591a8a8 100644
--- a/vm/interpreter_test.go
+++ b/vm/interpreter_test.go
@@ -45,7 +45,7 @@ func TestAllRegressionTests(t *testing.T) {
 			if err != nil {
 				t.Fatalf("Compiling patch failed: %v", err)
 			}
-			buffer, err := sointu.Play(synth, song)
+			buffer, _, err := sointu.Play(synth, song)
 			buffer = buffer[:song.Score.LengthInRows()*song.SamplesPerRow()*2] // extend to the nominal length always.
 			if err != nil {
 				t.Fatalf("Play failed: %v", err)
diff --git a/vm/opcodes.go b/vm/opcodes.go
index 8d14d10..4677386 100644
--- a/vm/opcodes.go
+++ b/vm/opcodes.go
@@ -30,7 +30,8 @@ const (
 	opReceive    = 26
 	opSend       = 27
 	opSpeed      = 28
-	opXch        = 29
+	opSync       = 29
+	opXch        = 30
 )
 
-var transformCounts = [...]int{0, 0, 1, 0, 5, 1, 4, 1, 5, 2, 1, 1, 0, 1, 0, 1, 0, 0, 2, 6, 1, 2, 1, 0, 0, 0, 1, 0, 0}
+var transformCounts = [...]int{0, 0, 1, 0, 5, 1, 4, 1, 5, 2, 1, 1, 0, 1, 0, 1, 0, 0, 2, 6, 1, 2, 1, 0, 0, 0, 1, 0, 0, 0}