High fidelity tape decks are usually built with switches or detectors for the different bias and equalization requirements for high performance tapes. The most common, iron oxide tapes (defined by an IEC standard as "Type I"), use 120 µs playback equalization, while chrome and cobalt-absorbed tapes (IEC Type II) require 70 µs playback equalization. The recording "bias" equalizations were also different (and had a much longer time constant). Sony tried a dual layer tape with both ferric oxide and chrome dioxide known as 'ferrichrome' (FeCr) (IEC Type III) but these were only available for a short time in the 1970s. Metal Cassettes (IEC Type IV), also use 70 µs playback equalization, and provide still further improvements in sound quality, as well as improved resistance to wear.[13]