diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index a5de550f..d14ea8f1 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -31,4 +31,17 @@ target_link_libraries(sfizz_tests PRIVATE sfizz::sfizz)
 sfizz_enable_lto_if_needed(sfizz_tests)
 # target_link_libraries(sfizz_tests PRIVATE absl::strings absl::str_format absl::flat_hash_map cnpy absl::span absl::algorithm)
 
+find_package(PkgConfig)
+if(PKGCONFIG_FOUND)
+    pkg_check_modules(JACK "jack")
+endif()
+find_package(Qt5 COMPONENTS Widgets)
+
+if(JACK_FOUND AND TARGET Qt5::Widgets)
+    add_executable(sfizz_demo_filters DemoFilters.cpp)
+    target_include_directories(sfizz_demo_filters PRIVATE ${JACK_INCLUDE_DIRS})
+    target_link_libraries(sfizz_demo_filters PRIVATE sfizz::sfizz Qt5::Widgets ${JACK_LIBRARIES})
+    set_target_properties(sfizz_demo_filters PROPERTIES AUTOUIC ON)
+endif()
+
 file(COPY "." DESTINATION ${CMAKE_BINARY_DIR}/tests)
diff --git a/tests/DemoFilters.cpp b/tests/DemoFilters.cpp
new file mode 100644
index 00000000..9bbf5900
--- /dev/null
+++ b/tests/DemoFilters.cpp
@@ -0,0 +1,325 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#include "sfizz/SfzFilter.h"
+#include "ui_DemoFilters.h"
+#include <QApplication>
+#include <QMainWindow>
+#include <QMessageBox>
+#include <QButtonGroup>
+#include <QDebug>
+#include <jack/jack.h>
+#include <memory>
+
+///
+struct jack_delete {
+    void operator()(jack_client_t *x) const noexcept { jack_client_close(x); }
+};
+
+typedef std::unique_ptr<jack_client_t, jack_delete> jack_client_u;
+
+///
+class DemoApp : public QApplication {
+public:
+    DemoApp(int &argc, char **argv);
+    bool initSound();
+    void initWindow();
+
+private:
+    static int processAudio(jack_nframes_t nframes, void *cbdata);
+
+private:
+    void valueChangedType(int value);
+    void valueChangedCutoff(int value);
+    void valueChangedResonance(int value);
+    void valueChangedPkShGain(int value);
+    void valueChangedBandwidth(int value);
+    void valueChangedFilterMode(int value);
+
+private:
+    QMainWindow *fWindow = nullptr;
+    Ui::DemoFiltersWindow fUi;
+
+    static constexpr int cutoffMin = 10.0;
+    static constexpr int cutoffMax = 20000.0;
+
+    static constexpr int resoMin = 0.0;
+    static constexpr int resoMax = 40.0;
+
+    static constexpr int pkshMin = -40.0;
+    static constexpr int pkshMax = 40.0;
+
+    static constexpr int bwMin = 1.0;
+    static constexpr int bwMax = 10.0;
+
+    int fType = sfz::kFilterNone;
+    int fCutoff = 500.0;
+    int fReso = 0.0;
+    int fPksh = 20.0;
+    int fBw = 1.0;
+
+    sfz::Filter fFilter;
+    sfz::FilterEq fFilterEq;
+
+    enum FilterMode {
+        kFilterModeMulti,
+        kFilterModeEq,
+    };
+    FilterMode fFilterMode = kFilterModeMulti;
+
+    jack_client_u fClient;
+    jack_port_t *fPorts[4] = {};
+};
+
+DemoApp::DemoApp(int &argc, char **argv)
+    : QApplication(argc, argv)
+{
+    setApplicationName(tr("Sfizz Filters"));
+}
+
+bool DemoApp::initSound()
+{
+    jack_client_t *client = jack_client_open(
+        applicationName().toUtf8().data(), JackNoStartServer, nullptr);
+    if (!client) {
+        QMessageBox::critical(nullptr, tr("Error"), tr("Cannot open JACK audio."));
+        return false;
+    }
+
+    fClient.reset(client);
+
+    double sampleRate = jack_get_sample_rate(client);
+
+    fFilter.init(sampleRate);
+    fFilter.setChannels(2);
+
+    fFilterEq.init(sampleRate);
+    fFilterEq.setChannels(2);
+
+    fPorts[0] = jack_port_register(client, "in_left", JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
+    fPorts[1] = jack_port_register(client, "in_right", JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
+    fPorts[2] = jack_port_register(client, "out_left", JACK_DEFAULT_AUDIO_TYPE, JackPortIsOutput, 0);
+    fPorts[3] = jack_port_register(client, "out_right", JACK_DEFAULT_AUDIO_TYPE, JackPortIsOutput, 0);
+
+    if (!(fPorts[0] && fPorts[1] && fPorts[2] && fPorts[3])) {
+        QMessageBox::critical(nullptr, tr("Error"), tr("Cannot register JACK ports."));
+        return false;
+    }
+
+    jack_set_process_callback(client, &processAudio, this);
+
+    if (jack_activate(client) != 0) {
+        QMessageBox::critical(nullptr, tr("Error"), tr("Cannot activate JACK client."));
+        return false;
+    }
+
+    return true;
+}
+
+void DemoApp::initWindow()
+{
+    QMainWindow *window = new QMainWindow;
+    fWindow = window;
+    fUi.setupUi(window);
+    window->setWindowTitle(applicationDisplayName());
+
+    QComboBox *cbTypes = fUi.comboBox;
+    cbTypes->addItem("None", static_cast<int>(sfz::kFilterNone));
+    cbTypes->addItem("Apf1p", static_cast<int>(sfz::kFilterApf1p));
+    cbTypes->addItem("Bpf1p", static_cast<int>(sfz::kFilterBpf1p));
+    cbTypes->addItem("Bpf2p", static_cast<int>(sfz::kFilterBpf2p));
+    cbTypes->addItem("Bpf4p", static_cast<int>(sfz::kFilterBpf4p));
+    cbTypes->addItem("Bpf6p", static_cast<int>(sfz::kFilterBpf6p));
+    cbTypes->addItem("Brf1p", static_cast<int>(sfz::kFilterBrf1p));
+    cbTypes->addItem("Brf2p", static_cast<int>(sfz::kFilterBrf2p));
+    cbTypes->addItem("Hpf1p", static_cast<int>(sfz::kFilterHpf1p));
+    cbTypes->addItem("Hpf2p", static_cast<int>(sfz::kFilterHpf2p));
+    cbTypes->addItem("Hpf4p", static_cast<int>(sfz::kFilterHpf4p));
+    cbTypes->addItem("Hpf6p", static_cast<int>(sfz::kFilterHpf6p));
+    cbTypes->addItem("Lpf1p", static_cast<int>(sfz::kFilterLpf1p));
+    cbTypes->addItem("Lpf2p", static_cast<int>(sfz::kFilterLpf2p));
+    cbTypes->addItem("Lpf4p", static_cast<int>(sfz::kFilterLpf4p));
+    cbTypes->addItem("Lpf6p", static_cast<int>(sfz::kFilterLpf6p));
+    cbTypes->addItem("Pink", static_cast<int>(sfz::kFilterPink));
+    cbTypes->addItem("Lpf2pSv", static_cast<int>(sfz::kFilterLpf2pSv));
+    cbTypes->addItem("Hpf2pSv", static_cast<int>(sfz::kFilterHpf2pSv));
+    cbTypes->addItem("Bpf2pSv", static_cast<int>(sfz::kFilterBpf2pSv));
+    cbTypes->addItem("Brf2pSv", static_cast<int>(sfz::kFilterBrf2pSv));
+    cbTypes->addItem("Lsh", static_cast<int>(sfz::kFilterLsh));
+    cbTypes->addItem("Hsh", static_cast<int>(sfz::kFilterHsh));
+    cbTypes->addItem("Peq", static_cast<int>(sfz::kFilterPeq));
+
+    cbTypes->setCurrentIndex(cbTypes->findData(fType));
+    fUi.lcdType->display(fType);
+
+    connect(
+        cbTypes, QOverload<int>::of(&QComboBox::currentIndexChanged),
+        this, [this, cbTypes](int index) { valueChangedType(cbTypes->itemData(index).toInt()); });
+
+    fUi.dialCutoff->setRange(cutoffMin, cutoffMax);
+    fUi.dialResonance->setRange(resoMin, resoMax);
+    fUi.dialPkShGain->setRange(pkshMin, pkshMax);
+    fUi.dialBandwidth->setRange(bwMin, bwMax);
+    fUi.spinCutoff->setRange(cutoffMin, cutoffMax);
+    fUi.spinResonance->setRange(resoMin, resoMax);
+    fUi.spinPkShGain->setRange(pkshMin, pkshMax);
+    fUi.spinBandwidth->setRange(bwMin, bwMax);
+
+    fUi.dialCutoff->setValue(fCutoff);
+    fUi.dialResonance->setValue(fReso);
+    fUi.dialPkShGain->setValue(fPksh);
+    fUi.dialBandwidth->setValue(fBw);
+    fUi.spinCutoff->setValue(fCutoff);
+    fUi.spinResonance->setValue(fReso);
+    fUi.spinPkShGain->setValue(fPksh);
+    fUi.spinBandwidth->setValue(fBw);
+
+    connect(
+        fUi.dialCutoff, &QDial::valueChanged,
+        this, [this](int value) { valueChangedCutoff(value); });
+    connect(
+        fUi.spinCutoff, QOverload<int>::of(&QSpinBox::valueChanged),
+        this, [this](int value) { valueChangedCutoff(value); });
+    connect(
+        fUi.dialResonance, &QDial::valueChanged,
+        this, [this](int value) { valueChangedResonance(value); });
+    connect(
+        fUi.spinResonance, QOverload<int>::of(&QSpinBox::valueChanged),
+        this, [this](int value) { valueChangedResonance(value); });
+    connect(
+        fUi.dialPkShGain, &QDial::valueChanged,
+        this, [this](int value) { valueChangedPkShGain(value); });
+    connect(
+        fUi.spinPkShGain, QOverload<int>::of(&QSpinBox::valueChanged),
+        this, [this](int value) { valueChangedPkShGain(value); });
+    connect(
+        fUi.dialBandwidth, &QDial::valueChanged,
+        this, [this](int value) { valueChangedBandwidth(value); });
+    connect(
+        fUi.spinBandwidth, QOverload<int>::of(&QSpinBox::valueChanged),
+        this, [this](int value) { valueChangedBandwidth(value); });
+
+    QButtonGroup *grpMode = new QButtonGroup(this);
+    grpMode->addButton(fUi.btnMultiMode, kFilterModeMulti);
+    grpMode->addButton(fUi.btnEqMode, kFilterModeEq);
+    fUi.btnMultiMode->setChecked(true);
+    grpMode->setExclusive(true);
+
+    connect(
+        grpMode, QOverload<int, bool>::of(&QButtonGroup::buttonToggled), this,
+        [this](int id, bool toggled) {
+            if (toggled)
+                valueChangedFilterMode(id);
+        });
+
+    window->adjustSize();
+    window->setFixedSize(window->size());
+
+    window->show();
+}
+
+int DemoApp::processAudio(jack_nframes_t nframes, void *cbdata)
+{
+    DemoApp *self = reinterpret_cast<DemoApp *>(cbdata);
+
+    const float *ins[2];
+    float *outs[2];
+
+    ins[0] = reinterpret_cast<float *>(jack_port_get_buffer(self->fPorts[0], nframes));
+    ins[1] = reinterpret_cast<float *>(jack_port_get_buffer(self->fPorts[1], nframes));
+    outs[0] = reinterpret_cast<float *>(jack_port_get_buffer(self->fPorts[2], nframes));
+    outs[1] = reinterpret_cast<float *>(jack_port_get_buffer(self->fPorts[3], nframes));
+
+    switch (self->fFilterMode) {
+    default:
+    case kFilterModeMulti:
+        self->fFilter.setType(static_cast<sfz::FilterType>(self->fType));
+        self->fFilter.process(ins, outs, self->fCutoff, self->fReso, self->fPksh, nframes);
+        break;
+    case kFilterModeEq:
+        self->fFilterEq.process(ins, outs, self->fCutoff, self->fBw, self->fPksh, nframes);
+        break;
+    }
+
+    return 0;
+}
+
+void DemoApp::valueChangedType(int value)
+{
+    fType = value;
+    fUi.lcdType->display(value);
+}
+
+void DemoApp::valueChangedCutoff(int value)
+{
+    fUi.dialCutoff->blockSignals(true);
+    fUi.dialCutoff->setValue(value);
+    fUi.dialCutoff->blockSignals(false);
+
+    fUi.spinCutoff->blockSignals(true);
+    fUi.spinCutoff->setValue(value);
+    fUi.spinCutoff->blockSignals(false);
+
+    fCutoff = value;
+}
+
+void DemoApp::valueChangedResonance(int value)
+{
+    fUi.dialResonance->blockSignals(true);
+    fUi.dialResonance->setValue(value);
+    fUi.dialResonance->blockSignals(false);
+
+    fUi.spinResonance->blockSignals(true);
+    fUi.spinResonance->setValue(value);
+    fUi.spinResonance->blockSignals(false);
+
+    fReso = value;
+}
+
+void DemoApp::valueChangedPkShGain(int value)
+{
+    fUi.dialPkShGain->blockSignals(true);
+    fUi.dialPkShGain->setValue(value);
+    fUi.dialPkShGain->blockSignals(false);
+
+    fUi.spinPkShGain->blockSignals(true);
+    fUi.spinPkShGain->setValue(value);
+    fUi.spinPkShGain->blockSignals(false);
+
+    fPksh = value;
+}
+
+void DemoApp::valueChangedBandwidth(int value)
+{
+    fUi.dialBandwidth->blockSignals(true);
+    fUi.dialBandwidth->setValue(value);
+    fUi.dialBandwidth->blockSignals(false);
+
+    fUi.spinBandwidth->blockSignals(true);
+    fUi.spinBandwidth->setValue(value);
+    fUi.spinBandwidth->blockSignals(false);
+
+    fBw = value;
+}
+
+void DemoApp::valueChangedFilterMode(int value)
+{
+    fUi.stackedWidget->setCurrentIndex(value);
+
+    fFilterMode = static_cast<FilterMode>(value);
+}
+
+int main(int argc, char *argv[])
+{
+    DemoApp app(argc, argv);
+
+    if (!app.initSound())
+        return 1;
+
+    app.initWindow();
+
+    return app.exec();
+}
diff --git a/tests/DemoFilters.ui b/tests/DemoFilters.ui
new file mode 100644
index 00000000..36281d1f
--- /dev/null
+++ b/tests/DemoFilters.ui
@@ -0,0 +1,239 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>DemoFiltersWindow</class>
+ <widget class="QMainWindow" name="DemoFiltersWindow">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>415</width>
+    <height>216</height>
+   </rect>
+  </property>
+  <widget class="QWidget" name="centralwidget">
+   <layout class="QGridLayout" name="gridLayout_2">
+    <item row="0" column="0">
+     <widget class="QDial" name="dialCutoff"/>
+    </item>
+    <item row="0" column="1">
+     <widget class="QDial" name="dialPkShGain"/>
+    </item>
+    <item row="0" column="2" rowspan="3">
+     <widget class="QStackedWidget" name="stackedWidget">
+      <property name="currentIndex">
+       <number>0</number>
+      </property>
+      <widget class="QWidget" name="widget">
+       <layout class="QGridLayout" name="gridLayout">
+        <property name="leftMargin">
+         <number>0</number>
+        </property>
+        <property name="topMargin">
+         <number>0</number>
+        </property>
+        <property name="rightMargin">
+         <number>0</number>
+        </property>
+        <property name="bottomMargin">
+         <number>0</number>
+        </property>
+        <item row="0" column="0">
+         <widget class="QDial" name="dialResonance"/>
+        </item>
+        <item row="0" column="1">
+         <widget class="QLCDNumber" name="lcdType">
+          <property name="digitCount">
+           <number>2</number>
+          </property>
+         </widget>
+        </item>
+        <item row="1" column="0">
+         <widget class="QSpinBox" name="spinResonance">
+          <property name="alignment">
+           <set>Qt::AlignCenter</set>
+          </property>
+          <property name="suffix">
+           <string> dB</string>
+          </property>
+         </widget>
+        </item>
+        <item row="1" column="1">
+         <widget class="QComboBox" name="comboBox"/>
+        </item>
+        <item row="2" column="0">
+         <widget class="QLabel" name="label_2">
+          <property name="text">
+           <string>Resonance</string>
+          </property>
+          <property name="alignment">
+           <set>Qt::AlignCenter</set>
+          </property>
+         </widget>
+        </item>
+        <item row="2" column="1">
+         <widget class="QLabel" name="label_3">
+          <property name="text">
+           <string>Type</string>
+          </property>
+          <property name="alignment">
+           <set>Qt::AlignCenter</set>
+          </property>
+         </widget>
+        </item>
+       </layout>
+      </widget>
+      <widget class="QWidget" name="widget">
+       <layout class="QGridLayout" name="gridLayout_3">
+        <property name="leftMargin">
+         <number>0</number>
+        </property>
+        <property name="topMargin">
+         <number>0</number>
+        </property>
+        <property name="rightMargin">
+         <number>0</number>
+        </property>
+        <property name="bottomMargin">
+         <number>0</number>
+        </property>
+        <item row="0" column="0">
+         <widget class="QDial" name="dialBandwidth"/>
+        </item>
+        <item row="2" column="0">
+         <widget class="QLabel" name="label_5">
+          <property name="text">
+           <string>Bandwidth</string>
+          </property>
+          <property name="alignment">
+           <set>Qt::AlignCenter</set>
+          </property>
+         </widget>
+        </item>
+        <item row="1" column="0">
+         <widget class="QSpinBox" name="spinBandwidth">
+          <property name="alignment">
+           <set>Qt::AlignCenter</set>
+          </property>
+          <property name="suffix">
+           <string> oct</string>
+          </property>
+         </widget>
+        </item>
+        <item row="0" column="1" rowspan="3">
+         <widget class="QWidget" name="widget" native="true"/>
+        </item>
+       </layout>
+      </widget>
+     </widget>
+    </item>
+    <item row="1" column="0">
+     <widget class="QSpinBox" name="spinCutoff">
+      <property name="alignment">
+       <set>Qt::AlignCenter</set>
+      </property>
+      <property name="suffix">
+       <string> Hz</string>
+      </property>
+     </widget>
+    </item>
+    <item row="1" column="1">
+     <widget class="QSpinBox" name="spinPkShGain">
+      <property name="alignment">
+       <set>Qt::AlignCenter</set>
+      </property>
+      <property name="suffix">
+       <string> dB</string>
+      </property>
+     </widget>
+    </item>
+    <item row="2" column="0">
+     <widget class="QLabel" name="label">
+      <property name="text">
+       <string>Cutoff</string>
+      </property>
+      <property name="alignment">
+       <set>Qt::AlignCenter</set>
+      </property>
+     </widget>
+    </item>
+    <item row="2" column="1">
+     <widget class="QLabel" name="label_4">
+      <property name="text">
+       <string>Peak/shelf gain</string>
+      </property>
+      <property name="alignment">
+       <set>Qt::AlignCenter</set>
+      </property>
+     </widget>
+    </item>
+    <item row="3" column="0" colspan="3">
+     <widget class="QFrame" name="frame">
+      <property name="frameShape">
+       <enum>QFrame::StyledPanel</enum>
+      </property>
+      <property name="frameShadow">
+       <enum>QFrame::Raised</enum>
+      </property>
+      <layout class="QHBoxLayout" name="horizontalLayout">
+       <item>
+        <spacer name="horizontalSpacer">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>20</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+       <item>
+        <widget class="QRadioButton" name="btnMultiMode">
+         <property name="text">
+          <string>Multi-mode</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <spacer name="horizontalSpacer_3">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>20</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+       <item>
+        <widget class="QRadioButton" name="btnEqMode">
+         <property name="text">
+          <string>Equalizer</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <spacer name="horizontalSpacer_2">
+         <property name="orientation">
+          <enum>Qt::Horizontal</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>40</width>
+           <height>20</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+      </layout>
+     </widget>
+    </item>
+   </layout>
+  </widget>
+ </widget>
+ <resources/>
+ <connections/>
+</ui>