diff --git a/Makefile b/Makefile
index f449fb8..2fb10fd 100644
--- a/Makefile
+++ b/Makefile
@@ -2,6 +2,7 @@ PROG=		sndlock
 SRCS=		imgui_impl_glfw.cpp imgui_impl_opengl3.cpp imgui_draw.cpp imgui_widgets.cpp imgui_tables.cpp imgui.cpp sndlock.cpp
 CXXOPTS=	`pkg-config --cflags glfw3 gl`
 LDFLAGS=	`pkg-config --libs glfw3 gl`
+LDADD=		-lsndio -lm
 
 BINDIR=		/usr/local/bin
 NOMAN=		noman
diff --git a/sndlock.cpp b/sndlock.cpp
index 23fa8dd..c4f3b77 100644
--- a/sndlock.cpp
+++ b/sndlock.cpp
@@ -1,11 +1,72 @@
 #include <iostream>
+#include <thread>
+#include <cstdint>
 
 #include <GLFW/glfw3.h>
+#include <sndio.h>
+#include <math.h>
 
 #include "imgui.h"
 #include "imgui_impl_glfw.h"
 #include "imgui_impl_opengl3.h"
 
+static std::atomic<bool> shutdown_threads;
+static std::atomic<float> frequency = 440.0f;
+
+#define SND_SIG 1
+#define SND_BITS 16
+#define SND_PCHAN 2
+#define SND_RATE 44100
+#define SND_BUFLEN 4096
+
+static void dsp_thread()
+{
+    struct sio_hdl *hdl;
+    struct sio_par par;
+
+    hdl = sio_open(SIO_DEVANY, SIO_PLAY, 0);
+    if(hdl == nullptr) {
+        std::cerr << "failed to open sound device" << std::endl;
+        return;
+    }
+    sio_initpar(&par);
+    par.sig = SND_SIG;
+    par.bits = SND_BITS;
+    par.pchan = SND_PCHAN;
+    par.rate = SND_RATE;
+    par.le = SIO_LE_NATIVE;
+    if(!sio_setpar(hdl, &par)) {
+        std::cerr << "failed to set sound device parameters" << std::endl;
+        sio_close(hdl);
+        return;
+    }
+
+    if(!sio_start(hdl)) {
+        std::cerr << "failed to start sound device" << std::endl;
+        sio_close(hdl);
+        return;
+    }
+
+    uint32_t phase = 0;
+    int16_t buf[SND_BUFLEN*SND_PCHAN];
+    while(!shutdown_threads) {
+        uint32_t ftw = frequency*(float)UINT32_MAX/SND_RATE;
+        for(int i=0;i<SND_BUFLEN;i++) {
+            buf[2*i] = buf[2*i+1] = (INT16_MAX-1)*sin(phase*2.0f*(float)M_PI/(float)UINT32_MAX);
+            phase += ftw;
+        }
+        if(!sio_write(hdl, buf, SND_BUFLEN*(SND_BITS/8)*SND_PCHAN)) {
+            std::cerr << "failed to write to sound device" << std::endl;
+            sio_stop(hdl);
+            sio_close(hdl);
+            return;
+        }
+    }
+
+    sio_stop(hdl);
+    sio_close(hdl);
+}
+
 int main(int argc, char* argv[])
 {
     if(!glfwInit()) {
@@ -41,6 +102,18 @@ int main(int argc, char* argv[])
     ImGui_ImplOpenGL3_Init("#version 130");
     std::atexit(ImGui_ImplOpenGL3_Shutdown);
 
+    static std::thread dsp_thread_h = std::thread(dsp_thread);
+    static auto JoinDSP = []() {
+        dsp_thread_h.join();
+    };
+    std::atexit(JoinDSP);
+
+    shutdown_threads = false;
+    static auto SetShutdown = []() {
+        shutdown_threads = true;
+    };
+    std::atexit(SetShutdown);
+
     bool exit = false;
     while(!exit && !glfwWindowShouldClose(window)) {
         glfwPollEvents();
@@ -56,6 +129,9 @@ int main(int argc, char* argv[])
         ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
         ImGui::Begin("sndlock", nullptr, ImGuiWindowFlags_NoDecoration | ImGuiWindowFlags_NoResize);
 
+        float frequency_l = frequency;
+        ImGui::SliderFloat("Frequency", &frequency_l, 50.0f, 8000.0f);
+        frequency = frequency_l;
         if(ImGui::Button("Exit"))
             exit = true;