Good question! From our friend Anoop at Sennheiser, please, read on! Sennheiser has updated the MB 660 series to include below improvement. The firmware will be available for download from the Sennheiser Updater Jan 26, 2017! New features - User configurable sidetone FAQ Q: What is sidetone? A: Sidetone is the audible feedback of your own voice while speaking. It helps you modulate your voice, speaking neither too loudly nor too quietly and gives a more pleasant user experience. Q: How to change the sidetone with the new firmware? A: The sidetone level can be changed in the Windows audio mixer by following below instructions. When you have updated the headset you keep the USB cable connected and go into the audio settings in Windows to change the sidetone. When you have increased the sidetone you can disconnect the USB cable and the headset will remember the new sidetone setting and will work with both USB and Bluetooth connections. Changing sidetone through USB interface is a tempora…