Sidetone is by default enabled for the JBL Quantum Stream Studio. You can lower the sidetone volume or mute it by pressing the multifunction knob until you are at the audio/voice balance function. Turn the knob towards the voice (microphone icon) to increase the audio volume and lower down the sidetone volume at the same time. Turn the knob towards the headphone icon to increase the sidetone volume and reduce the audio volume.