diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4f349a8c6..bc8ffb27f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -73,9 +73,11 @@ set(WITH_RENDER_OPENGL_DEFAULT ON)
 if (WIN32)
   set(WITH_RENDER_DX11_DEFAULT ON)
   set(WITH_RENDER_DX9_DEFAULT ON)
+  set(WITH_ASIO_DEFAULT ON)
 else()
   set(WITH_RENDER_DX11_DEFAULT OFF)
   set(WITH_RENDER_DX9_DEFAULT OFF)
+  set(WITH_ASIO_DEFAULT OFF)
 endif()
 if (APPLE)
   set(WITH_RENDER_METAL_DEFAULT ON)
@@ -116,6 +118,7 @@ option(USE_MOMO "Build a libintl implementation instead of using the system one.
 option(WITH_OGG "Whether to build with Ogg and Vorbis support." ${WITH_OGG_DEFAULT})
 option(WITH_MPEG "Whether to build with MPEG audio support (including MP3)." ${WITH_MPEG_DEFAULT})
 option(WITH_JACK "Whether to build with JACK support. Auto-detects if JACK is available" ${WITH_JACK_DEFAULT})
+option(WITH_ASIO "Whether to build with ASIO support. Upgrades Furnace license to GPLv3." ${WITH_ASIO_DEFAULT})
 option(WITH_PORTAUDIO "Whether to build with PortAudio for audio output." ${WITH_PORTAUDIO_DEFAULT})
 option(WITH_RENDER_SDL "Whether to build with the SDL_Renderer render backend." ${WITH_RENDER_SDL_DEFAULT})
 option(WITH_RENDER_OPENGL "Whether to build with the OpenGL render backend." ${WITH_RENDER_OPENGL_DEFAULT})
@@ -508,6 +511,25 @@ else()
   message(STATUS "Building without JACK support")
 endif()
 
+if (WITH_ASIO)
+  if (NOT WIN32)
+    message(FATAL_ERROR "ASIO is only available on Windows!")
+  endif()
+  add_subdirectory(extern/asio)
+  list(APPEND DEPENDENCIES_DEFINES HAVE_ASIO)
+  list(APPEND DEPENDENCIES_DEFINES FURNACE_GPL3)
+  list(APPEND AUDIO_SOURCES src/audio/asio.cpp)
+  list(APPEND DEPENDENCIES_INCLUDE_DIRS extern/asio/common extern/asio/host)
+  list(APPEND DEPENDENCIES_LIBRARIES ASIO)
+  message(STATUS "Building with ASIO support")
+  set(FURNACE_LICENSE "GPLv3")
+else()
+  if (WIN32)
+    message(STATUS "Building without ASIO support")
+  endif()
+  set(FURNACE_LICENSE "GPLv2")
+endif()
+
 if (WITH_PORTAUDIO)
   list(APPEND AUDIO_SOURCES src/audio/pa.cpp)
   message(STATUS "Building with PortAudio")
@@ -1365,3 +1387,5 @@ if (NOT ANDROID OR TERMUX)
 endif()
 
 target_compile_definitions(${FURNACE} PRIVATE ${DEPENDENCIES_DEFINES})
+
+message(STATUS "License: ${FURNACE_LICENSE}")
diff --git a/README.md b/README.md
index 7841b8cd3..43df88555 100644
--- a/README.md
+++ b/README.md
@@ -148,7 +148,7 @@ for other operating systems, you may [build the source](#developer-info).
   - built-in sample editor
   - chip mixing settings
   - built-in visualizer in pattern view
-- open-source under GPLv2 or later.
+- open-source under GPLv2 or later/GPLv3. see [LICENSE](LICENSE).
 
 ---
 
diff --git a/src/audio/asio.cpp b/src/audio/asio.cpp
new file mode 100644
index 000000000..e9379dc3a
--- /dev/null
+++ b/src/audio/asio.cpp
@@ -0,0 +1,278 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2025 tildearrow and contributors
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <string.h>
+#include "asio.h"
+#include "../ta-log.h"
+
+static TAAudioASIO* callbackInstance=NULL;
+
+static void _onBufferSwitch(long index, ASIOBool isDirect) {
+  if (callbackInstance==NULL) return;
+  callbackInstance->onProcess(index);
+}
+
+static void _onSampleRate(ASIOSampleRate rate) {
+  if (callbackInstance==NULL) return;
+  callbackInstance->onSampleRate(*(double*)(&rate));
+}
+
+static long _onMessage(long type, long value, void* msg, double* opt) {
+  return 0;
+}
+
+void TAAudioASIO::onSampleRate(double rate) {
+  sampleRateChanged(SampleRateChangeEvent(rate));
+}
+
+void TAAudioASIO::onBufferSize(int bufsize) {
+  bufferSizeChanged(BufferSizeChangeEvent(bufsize));
+}
+
+void TAAudioASIO::onProcess(int index) {
+  if (audioProcCallback!=NULL) {
+    if (midiIn!=NULL) midiIn->gather();
+    audioProcCallback(audioProcCallbackUser,inBufs,outBufs,desc.inChans,desc.outChans,desc.bufsize);
+  }
+
+  // upload here...
+
+  /*if (nframes!=desc.bufsize) {
+    desc.bufsize=nframes;
+  }*/
+}
+
+void* TAAudioASIO::getContext() {
+  return (void*)&driverInfo;
+}
+
+bool TAAudioASIO::quit() {
+  if (!initialized) return false;
+
+  if (running) {
+    ASIOStop();
+    running=false;
+  }
+
+  ASIODisposeBuffers();
+  
+  for (int i=0; i<desc.inChans; i++) {
+    delete[] inBufs[i];
+    inBufs[i]=NULL;
+  }
+  for (int i=0; i<desc.outChans; i++) {
+    delete[] outBufs[i];
+    outBufs[i]=NULL;
+  }
+
+  delete[] inBufs;
+  delete[] outBufs;
+  inBufs=NULL;
+  outBufs=NULL;
+
+  ASIOExit();
+  drivers.removeCurrentDriver();
+
+  callbackInstance=NULL;
+  initialized=false;
+
+  return true;
+}
+
+bool TAAudioASIO::setRun(bool run) {
+  if (!initialized) return false;
+  if (running==run) {
+    return running;
+  }
+  if (run) {
+    if (ASIOStart()!=ASE_OK) return false;
+    running=true;
+  } else {
+    // does it matter whether stop was successful?
+    ASIOStop();
+    running=false;
+  }
+  return running;
+}
+
+bool TAAudioASIO::init(TAAudioDesc& request, TAAudioDesc& response) {
+  if (initialized) return false;
+  if (callbackInstance) {
+    logE("can't initialize more than one output!");
+    return false;
+  }
+
+  desc=request;
+  desc.outFormat=TA_AUDIO_FORMAT_F32;
+
+  if (desc.deviceName.empty()) {
+    // load first driver if not specified
+    logV("getting driver names...");
+    driverCount=drivers.getDriverNames(driverNames,ASIO_DRIVER_MAX);
+
+    // quit if we couldn't find any drivers
+    if (driverCount<1) {
+      logE("no ASIO drivers available");
+      return false;
+    }
+
+    desc.deviceName=driverNames[0];
+  }
+
+  // load driver
+  logV("loading ASIO driver...");
+  strncpy(deviceNameCopy,desc.deviceName.c_str(),63);
+  if (!drivers.loadDriver(deviceNameCopy)) {
+    logE("failed to load ASIO driver!");
+    return false;
+  }
+
+  // init
+  memset(&driverInfo,0,sizeof(driverInfo));
+  memset(bufInfo,0,sizeof(ASIOBufferInfo)*ASIO_CHANNEL_MAX*2);
+  memset(chanInfo,0,sizeof(ASIOChannelInfo)*ASIO_CHANNEL_MAX*2);
+  driverInfo.asioVersion=2;
+  driverInfo.sysRef=NULL;
+  ASIOError result=ASIOInit(&driverInfo);
+
+  if (result!=ASE_OK) {
+    logE("could not init device!");
+    drivers.removeCurrentDriver();
+    return false;
+  }
+
+  // setup callbacks
+  // unfortunately, only one TAAudio instance may exist at a time when using ASIO...
+  callbackInstance=this;
+  memset(&callbacks,0,sizeof(ASIOCallbacks));
+  callbacks.bufferSwitch=_onBufferSwitch;
+  callbacks.sampleRateDidChange=_onSampleRate;
+  callbacks.asioMessage=_onMessage;
+
+  // get driver information
+  long maxInChans=0;
+  long maxOutChans=0;
+
+  result=ASIOGetChannels(&maxInChans,&maxOutChans);
+  if (result!=ASE_OK) {
+    logE("could not get channel count!");
+    ASIOExit();
+    drivers.removeCurrentDriver();
+    return false;
+  }
+
+  if (maxInChans>ASIO_CHANNEL_MAX) maxInChans=ASIO_CHANNEL_MAX;
+  if (maxOutChans>ASIO_CHANNEL_MAX) maxOutChans=ASIO_CHANNEL_MAX;
+
+  if (desc.inChans>maxInChans) desc.inChans=maxInChans;
+  if (desc.outChans>maxOutChans) desc.outChans=maxOutChans;
+
+  long minBufSize=0;
+  long maxBufSize=0;
+  long actualBufSize=0;
+  long bufSizeGranularity=0;
+  result=ASIOGetBufferSize(&minBufSize,&maxBufSize,&actualBufSize,&bufSizeGranularity);
+  if (result!=ASE_OK) {
+    logE("could not get buffer size!");
+    ASIOExit();
+    drivers.removeCurrentDriver();
+    return false;
+  }
+
+  ASIOSampleRate outRate;
+  result=ASIOGetSampleRate(&outRate);
+  if (result!=ASE_OK) {
+    logE("could not get sample rate!");
+    ASIOExit();
+    drivers.removeCurrentDriver();
+    return false;
+  }
+  desc.rate=*(double*)(&outRate);
+
+  totalChans=0;
+
+  if (desc.inChans>0) {
+    inBufs=new float*[desc.inChans];
+    for (int i=0; i<desc.inChans; i++) {
+      chanInfo[totalChans].channel=i;
+      chanInfo[totalChans].isInput=ASIOTrue;
+      ASIOGetChannelInfo(&chanInfo[totalChans]);
+      bufInfo[totalChans].channelNum=i;
+      bufInfo[totalChans++].isInput=ASIOTrue;
+      inBufs[i]=new float[actualBufSize];
+    }
+  }
+  if (desc.outChans>0) {
+    outBufs=new float*[desc.outChans];
+    for (int i=0; i<desc.outChans; i++) {
+      chanInfo[totalChans].channel=i;
+      chanInfo[totalChans].isInput=ASIOFalse;
+      ASIOGetChannelInfo(&chanInfo[totalChans]);
+      bufInfo[totalChans].channelNum=i;
+      bufInfo[totalChans++].isInput=ASIOTrue;
+      outBufs[i]=new float[actualBufSize];
+    }
+  }
+
+  result=ASIOCreateBuffers(bufInfo,totalChans,actualBufSize,&callbacks);
+  if (result!=ASE_OK) {
+    logE("could not create buffers!");
+    if (inBufs!=NULL) {
+      for (int i=0; i<desc.inChans; i++) {
+        if (inBufs[i]!=NULL) {
+          delete[] inBufs[i];
+          inBufs[i]=NULL;
+        }
+      }
+      delete[] inBufs;
+      inBufs=NULL;
+    }
+    if (outBufs!=NULL) {
+      for (int i=0; i<desc.outChans; i++) {
+        if (outBufs[i]!=NULL) {
+          delete[] outBufs[i];
+          outBufs[i]=NULL;
+        }
+      }
+      delete[] outBufs;
+      outBufs=NULL;
+    }
+    ASIOExit();
+    drivers.removeCurrentDriver();
+    return false;
+  }
+
+  desc.bufsize=actualBufSize;
+  desc.fragments=2;
+
+  response=desc;
+  initialized=true;
+  return true;
+}
+
+std::vector<String> TAAudioASIO::listAudioDevices() {
+  std::vector<String> ret;
+  memset(driverNames,0,sizeof(void*)*ASIO_DRIVER_MAX);
+  driverCount=drivers.getDriverNames(driverNames,ASIO_DRIVER_MAX);
+  for (int i=0; i<driverCount; i++) {
+    ret.push_back(driverNames[i]);
+  }
+
+  return ret;
+}
diff --git a/src/audio/asio.h b/src/audio/asio.h
new file mode 100644
index 000000000..4e46effcd
--- /dev/null
+++ b/src/audio/asio.h
@@ -0,0 +1,55 @@
+/**
+ * Furnace Tracker - multi-system chiptune tracker
+ * Copyright (C) 2021-2025 tildearrow and contributors
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "taAudio.h"
+#include <asiodrivers.h>
+#include <asio.h>
+
+#define ASIO_DRIVER_MAX 64
+#define ASIO_CHANNEL_MAX 16
+
+class TAAudioASIO: public TAAudio {
+  AsioDrivers drivers;
+  ASIODriverInfo driverInfo;
+  ASIOBufferInfo bufInfo[ASIO_CHANNEL_MAX*2];
+  ASIOChannelInfo chanInfo[ASIO_CHANNEL_MAX*2];
+  ASIOCallbacks callbacks;
+  int totalChans;
+
+  char* driverNames[ASIO_DRIVER_MAX];
+  int driverCount;
+
+  char deviceNameCopy[64];
+
+  public:
+    void onSampleRate(double rate);
+    void onBufferSize(int bufsize);
+    void onProcess(int nframes);
+
+    void* getContext();
+    bool quit();
+    bool setRun(bool run);
+    bool init(TAAudioDesc& request, TAAudioDesc& response);
+
+    std::vector<String> listAudioDevices();
+
+    TAAudioASIO():
+      totalChans(0),
+      driverCount(0) {}
+};
diff --git a/src/gui/about.cpp b/src/gui/about.cpp
index 2032a9a7d..3e7d77799 100644
--- a/src/gui/about.cpp
+++ b/src/gui/about.cpp
@@ -196,8 +196,13 @@ const char* aboutLine[]={
   "",
   _N("copyright © 2021-2025 tildearrow"),
   _N("(and contributors)."),
+#ifdef FURNACE_GPL3
+  _N("licensed under GPLv3! see"),
+  _N("LICENSE for more information."),
+#else
   _N("licensed under GPLv2+! see"),
   _N("LICENSE for more information."),
+#endif
   "",
   _N("help Furnace grow:"),
   "https://github.com/tildearrow/furnace",
@@ -213,6 +218,10 @@ const char* aboutLine[]={
   _N("the original program."),
   "",
   _N("it also comes with ABSOLUTELY NO WARRANTY."),
+#ifdef HAVE_ASIO
+  "",
+  _N("ASIO is a registered trademark of Steinberg Media Technologies GmbH."),
+#endif
   "",
   _N("thanks to all contributors/bug reporters!")
 };
diff --git a/src/main.cpp b/src/main.cpp
index 35c8be5e4..371ecec49 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -274,8 +274,13 @@ TAParamResult pLogLevel(String val) {
 TAParamResult pVersion(String) {
   printf("Furnace version " DIV_VERSION ".\n\n");
   printf("copyright (C) 2021-2025 tildearrow and contributors.\n");
+#ifdef FURNACE_GPL3
+  printf("licensed under the GNU General Public License version 3\n");
+  printf("<https://www.gnu.org/licenses/gpl-3.0.en.html>.\n\n");
+#else
   printf("licensed under the GNU General Public License version 2 or later\n");
   printf("<https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>.\n\n");
+#endif
   printf("this is free software with ABSOLUTELY NO WARRANTY.\n");
   printf("pass the -warranty parameter for more information.\n\n");
   printf("DISCLAIMER: this program is not affiliated with Delek in any form.\n");
@@ -296,6 +301,9 @@ TAParamResult pVersion(String) {
   printf("- zlib by Jean-loup Gailly and Mark Adler (zlib license)\n");
   printf("- PortAudio (PortAudio license)\n");
   printf("- Weak-JACK by x42 (GPLv2)\n");
+#ifdef HAVE_ASIO
+  printf("- ASIO® by Steinberg (GPLv3)\n");
+#endif
   printf("- RtMidi by Gary P. Scavone (RtMidi license)\n");
   printf("- backward-cpp by Google (MIT)\n");
   printf("- Dear ImGui by Omar Cornut (MIT)\n");
@@ -360,10 +368,26 @@ TAParamResult pVersion(String) {
   printf("- SID2 emulator by LTVA (GPLv2, modification of reSID emulator)\n");
   printf("- SID3 emulator by LTVA (MIT)\n");
   printf("- openMSX YMF278 emulator (modified version) by the openMSX developers (GPLv2)\n");
+#ifdef HAVE_ASIO
+  printf("\nASIO is a registered trademark of Steinberg Media Technologies GmbH.\n");
+#endif
   return TA_PARAM_QUIT;
 }
 
 TAParamResult pWarranty(String) {
+#ifdef FURNACE_GPL3
+  printf("This program is free software: you can redistribute it and/or modify\n"
+         "it under the terms of the GNU General Public License as published by\n"
+         "the Free Software Foundation, version 3.\n\n"
+
+         "This program is distributed in the hope that it will be useful,\n"
+         "but WITHOUT ANY WARRANTY; without even the implied warranty of\n"
+         "MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the\n"
+         "GNU General Public License for more details.\n\n"
+
+         "You should have received a copy of the GNU General Public License\n"
+         "along with this program.  If not, see <https://www.gnu.org/licenses/>.\n");
+#else
   printf("This program is free software; you can redistribute it and/or\n"
          "modify it under the terms of the GNU General Public License\n"
          "as published by the Free Software Foundation; either version 2\n"
@@ -377,6 +401,7 @@ TAParamResult pWarranty(String) {
          "You should have received a copy of the GNU General Public License\n"
          "along with this program; if not, write to the Free Software\n"
          "Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.\n");
+#endif
   return TA_PARAM_QUIT;
 }