The M4U 8 model allows you to listen to music wirelessly with Bluetooth® aptX™ HD - the latest 24-bit high definition version of the most universal wireless technology - the high fidelity version of Bluetooth. There are also two different wired modes of operation; 3.5mm wired connection, or via USB from the computer, which recharges the batteries for wireless operation. Active Noise Cancellation (ANC) is remarkably sophisticated and effective, utilizing 4 microphones (others use only 2) which offer 'Transparency Mode' allowing you to momentarily listen to the outside world as well as the ability to answer your connected phone. There is also an Active Mode, and Passive Mode (without batteries). Listen all day and all night with up to 15 hours of run time in Bluetooth or Active modes. When you're out of batteries, switch to Passive Mode without missing a beat.