Sony MDRNC500D Digital Noise-Canceling Headphone (Black) (Discontinued by Manufacturer) World'S First Headphone With Digital Technology For Precise Noise Canceling Up To 99.7% Noise Reduction At 160 Hz Artificial Intelligence (Ai) Noise Canceling With Automatic Selection Between 3 Different Environment Modes Internal Li-Ion Battery For Up To 16 Hours Of Use, Plus Allows For Use Of Aa Batteries For Even Longer Operation Built-In Monitor Switch Lets You Silence The Audio To Listen To Outside World's first digital noise canceling headphones Artificial Intelligence noise canceling Automatic selection between 3 different environments Digital EQ - accurate sound & wide frequency response Monitor switch to let surrounding sounds be heard