diff --git a/src/index.css b/src/index.css
index 232fced..7c19cf8 100644
--- a/src/index.css
+++ b/src/index.css
@@ -38,6 +38,23 @@ button, .button {
 
   background: black;
   color: white;
+
+  &:disabled {
+    opacity: 0.7;
+  }
+}
+
+input[type="number"] {
+  background: transparent;
+  color: white;
+  border: 1px solid white;
+  border-radius: 4px;
+  padding: 0.2em;
+
+  &:disabled {
+    opacity: 0.7;
+    pointer-events: none;
+  }
 }
 
 select {
diff --git a/src/routes/audio/+page.svelte b/src/routes/audio/+page.svelte
index 1bb0fd7..2f42fe0 100644
--- a/src/routes/audio/+page.svelte
+++ b/src/routes/audio/+page.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
 	import StereoTest from './(channels)/stereo-test.svelte';
+	import PhaseTest from './phase.svelte';
 </script>
 
 <article>
@@ -15,6 +16,8 @@
 			<li><a class="button" href="channels-7.1">7.1 Surround</a></li>
 		</ul>
 	</section>
+	<h3>Phase test</h3>
+	<PhaseTest />
 </article>
 
 <style>
diff --git a/src/routes/audio/phase.svelte b/src/routes/audio/phase.svelte
new file mode 100644
index 0000000..87900cc
--- /dev/null
+++ b/src/routes/audio/phase.svelte
@@ -0,0 +1,91 @@
+<script lang="ts">
+	import { onMount } from 'svelte';
+
+	let frequency = 60;
+	let playing = false;
+
+	let audioCtx: AudioContext | undefined;
+	let oscillatorL: OscillatorNode | undefined;
+	let oscillatorR: OscillatorNode | undefined;
+
+	onMount(() => {
+		audioCtx = new window.AudioContext();
+	});
+
+	function start(mode: 'inPhase' | 'outOfPhase') {
+		if (!audioCtx) return;
+		oscillatorL?.stop();
+		oscillatorR?.stop();
+
+		oscillatorL = audioCtx.createOscillator();
+		oscillatorR = audioCtx.createOscillator();
+		const gainNode = audioCtx.createGain();
+
+		const stereoPannerL = audioCtx.createStereoPanner();
+		const stereoPannerR = audioCtx.createStereoPanner();
+
+		oscillatorL.frequency.setValueAtTime(frequency, audioCtx.currentTime);
+		oscillatorR.frequency.setValueAtTime(frequency, audioCtx.currentTime);
+
+		stereoPannerL.pan.setValueAtTime(-1, audioCtx.currentTime);
+		stereoPannerR.pan.setValueAtTime(1, audioCtx.currentTime);
+
+		oscillatorL.connect(stereoPannerL).connect(audioCtx.destination);
+		oscillatorR.connect(gainNode).connect(stereoPannerR).connect(audioCtx.destination);
+
+		if (mode === 'inPhase') {
+			gainNode?.gain.setValueAtTime(1, audioCtx.currentTime); // Normal phase
+		} else {
+			gainNode?.gain.setValueAtTime(-1, audioCtx.currentTime); // Invert phase
+		}
+
+		oscillatorL?.start();
+		oscillatorR?.start();
+		playing = true;
+	}
+
+	async function stop() {
+		oscillatorL?.stop();
+		oscillatorR?.stop();
+		playing = false;
+	}
+</script>
+
+<div class="test">
+	<label>
+		Frequency <input
+			type="number"
+			bind:value={frequency}
+			min="20"
+			max="20000"
+			disabled={playing}
+		/>Hz
+	</label>
+	<div class="controls">
+		<button on:click={() => start('inPhase')}>In Phase</button>
+		<button on:click={() => start('outOfPhase')}>Out of Phase</button>
+		<button class="stop" on:click={stop} disabled={!playing}>Stop</button>
+	</div>
+</div>
+
+<style>
+	.test {
+		margin: 1em 0;
+	}
+
+	.controls {
+		margin-top: 0.5em;
+	}
+
+	.stop {
+		margin-left: 1em;
+
+		&:not(:disabled) {
+			background: darkred;
+		}
+	}
+
+	input {
+		width: 5em;
+	}
+</style>