diff --git a/diagnostic/index.html b/diagnostic/index.html
index 85ff06d..f1696cd 100644
--- a/diagnostic/index.html
+++ b/diagnostic/index.html
@@ -145,6 +145,15 @@
       </div>
       <textarea id="voice-preview-text" rows="4"
         style="background:#0D0D1A;border:1px solid #2A2A3E;border-radius:6px;padding:10px;color:#fff;font-size:13px;resize:vertical;"></textarea>
+
+      <div style="display:flex;align-items:center;gap:10px;font-size:12px;color:#8888AA;">
+        <span style="min-width:120px;">Geschwindigkeit:</span>
+        <button onclick="adjustPreviewSpeed(-0.1)" class="btn secondary" style="padding:4px 10px;font-size:12px;">−0.1</button>
+        <span id="voice-preview-speed-value" style="min-width:52px;text-align:center;color:#fff;font-weight:600;">1.0 x</span>
+        <button onclick="adjustPreviewSpeed(0.1)" class="btn secondary" style="padding:4px 10px;font-size:12px;">+0.1</button>
+        <span style="color:#555570;font-size:11px;">(nur fuer dieses Modal, wird nicht gespeichert)</span>
+      </div>
+
       <div style="display:flex;gap:8px;align-items:center;">
         <button id="voice-preview-play" onclick="playVoicePreview()" class="btn primary" style="padding:8px 16px;">
           ▶ Abspielen
@@ -1630,10 +1639,29 @@
 
     // ── Voice Preview Modal ─────────────────────────
     const VOICE_PREVIEW_DEFAULT = 'Hallo, ich bin ARIA. Das hier ist ein kleiner Test damit du meine Stimme beurteilen kannst.';
+    const PREVIEW_SPEED_DEFAULT = 1.0;
+    const PREVIEW_SPEED_MIN = 0.1;
+    const PREVIEW_SPEED_MAX = 5.0;
     let currentPreviewVoice = '';
+    let currentPreviewSpeed = PREVIEW_SPEED_DEFAULT;
+
+    function _refreshPreviewSpeedLabel() {
+      const el = document.getElementById('voice-preview-speed-value');
+      if (el) el.textContent = currentPreviewSpeed.toFixed(1) + ' x';
+    }
+
+    function adjustPreviewSpeed(delta) {
+      const next = Math.round((currentPreviewSpeed + delta) * 10) / 10;
+      if (next < PREVIEW_SPEED_MIN || next > PREVIEW_SPEED_MAX) return;
+      currentPreviewSpeed = next;
+      _refreshPreviewSpeedLabel();
+    }
 
     function openVoicePreview(name) {
       currentPreviewVoice = name;
+      // Speed bei jedem Oeffnen zuruecksetzen — bewusst kein persist
+      currentPreviewSpeed = PREVIEW_SPEED_DEFAULT;
+      _refreshPreviewSpeedLabel();
       document.getElementById('voice-preview-name').textContent = name;
       // Text bei jedem Oeffnen zuruecksetzen
       document.getElementById('voice-preview-text').value = VOICE_PREVIEW_DEFAULT;
@@ -1658,7 +1686,12 @@
       }
       document.getElementById('voice-preview-status').textContent = '⏳ Rendere...';
       document.getElementById('voice-preview-play').disabled = true;
-      send({ action: 'preview_voice', voice: currentPreviewVoice, text });
+      send({
+        action: 'preview_voice',
+        voice: currentPreviewVoice,
+        text,
+        speed: currentPreviewSpeed,
+      });
     }
 
     function deleteXttsVoice(name) {
diff --git a/diagnostic/server.js b/diagnostic/server.js
index 06f6b44..59b1911 100644
--- a/diagnostic/server.js
+++ b/diagnostic/server.js
@@ -1469,7 +1469,7 @@ wss.on("connection", (ws) => {
       } else if (msg.action === "test_tts") {
         handleTestTTS(ws, msg.text || "Test");
       } else if (msg.action === "preview_voice") {
-        handleVoicePreview(ws, msg.voice || "", msg.text || "Hallo.");
+        handleVoicePreview(ws, msg.voice || "", msg.text || "Hallo.", msg.speed);
       } else if (msg.action === "check_tts") {
         handleCheckTTS(ws);
       } else if (msg.action === "check_desktop") {
@@ -1704,8 +1704,11 @@ function _handlePreviewChunk(payload) {
   }
 }
 
-async function handleVoicePreview(clientWs, voice, text) {
+async function handleVoicePreview(clientWs, voice, text, speed) {
   try {
+    // Speed clampen — Browser-Slider ist 0.1-5.0
+    let spd = parseFloat(speed);
+    if (!isFinite(spd) || spd < 0.1 || spd > 5.0) spd = 1.0;
     const requestId = crypto.randomUUID();
     _previewPending.set(requestId, { clientWs, chunks: [], sampleRate: 0, channels: 0 });
     // Timeout safety net
@@ -1720,10 +1723,10 @@ async function handleVoicePreview(clientWs, voice, text) {
         }
       }
     }, 60000);
-    log("info", "server", `Voice-Preview: voice="${voice}" text="${text.slice(0, 60)}"`);
+    log("info", "server", `Voice-Preview: voice="${voice}" speed=${spd.toFixed(1)}x text="${text.slice(0, 60)}"`);
     sendToRVS_raw({
       type: "xtts_request",
-      payload: { text, language: "de", requestId, voice, speed: 1.0 },
+      payload: { text, language: "de", requestId, voice, speed: spd },
       timestamp: Date.now(),
     });
   } catch (err) {