diff --git a/lib/synth-audio.js b/lib/synth-audio.js
index 63c2e48..73741ac 100644
--- a/lib/synth-audio.js
+++ b/lib/synth-audio.js
@@ -1316,6 +1316,7 @@ const synthCartesia = async(logger, {
     if (embedding) params += `,embedding=${embedding}`;
     if (opts.speed) params += `,speed=${opts.speed}`;
     if (opts.emotion) params += `,emotion=${opts.emotion}`;
+    if (opts.volume) params += `,volume=${opts.volume}`;
     params += '}';
 
     return {