Digital Object Identifier 10.1109/MSP.2014.2369191 Date of publication: 12 February 2015 IEEE SIGNAL PROCESSING MAGAZINE [92] MARCH 2015 1053-5888/15©2015IEEE H istorically, headphones have mainly been used for analytic listening in music production and in homes. During the last decade, with the boom of dedicated music players and mobile phones, the everyday use of light headphones has become highly popular. Current headphones are also paving the way for more sophisticated assisted listening devices. Today, active noise con- trol (ANC), equalization techniques, and a hear-through function are already a standard part of many headphones that people com- monly use while traveling. It is not difficult to predict that, in the near future, a headset will be a “hearing aid for those with normal hearing,” which can improve listening conditions for example in a noisy environment. Additionally, mobile augmented reality has become a hot topic [1], and new products such as the Google Glass will make it more common. On the audio side of augmented reality systems, mixing of the ambient and reproduced sounds will be an essential fea- ture. Augmented reality headsets may also serve as the main user interface for the disappearing computer in the future, when visual displays and tangible keyboards vanish. This article gives an overview of various signal processing techniques needed in assisted listening. The basic use case and various others are described in Figure 1, which shows how head- phone listening can be extended by incorporating external micro- phones and some signal processing. Assisted listening in heavy background noise environments, such as in an airplane, can be implemented using ANC [2]. HEADPHONE LISTENING IN A NOISY ENVIRONMENT When headphones are used in a noisy environment, their design goals are somewhat different than those of a conventional pair of high-fidelity (hi-fi) headphones. The most important feature of mobile headphones is the noise isolation capability, which can be passive or enhanced with ANC. Furthermore, the headphone fre- quency response can be designed to manage noisy environments, typically by boosting the bass end of the response, as natural ambient sounds have most of their energy at low frequencies (such as bus or airplane noise) and headphones usually attenuate low frequencies the least. EAR PHOTO—©ISTOCKPHOTO.COM/XRENDER ASSISTED LISTENING SIGN—© ISTOCKPHOTO.COM/NCANDRE EARPHONES—IMAGE LICENSED BY INGRAM PUBLISHING [ Vesa Välimäki, Andreas Franck, Jussi Rämö, Hannes Gamper, and Lauri Savioja ] [ Enhancing audio perception in real, augmented, and virtual environments ] Assisted Listening Using a Headset