Improving hearing aids through listening tests in a virtual sound environment

Simulating the real world in the lab OCTOBER 2010 • VOL. 63 • NO. 10 Complex acoustic environments are encountered frequently in everyday life, including, for example, in train stations, supermarkets, and busy restaurants. People with normal hearing can usually communicate without effort in these environments, but people with a hearing impairment often have difficulties, even when wearing hearing aids. Digital hearing aids are gradually becoming more powerful, though, and more advanced signal processing can be provided to help those who wear them. However, to develop these new processing methods it is important to perform listening tests in these difficult listening situations. Traditional hearing aid testing in the laboratory normally focuses on how well speech is understood in noise. However, there is much more to the experience of sound in everyday life. Specifically, the spatial aspects of sound, such as from which direction a sound comes or how far away a sound object is, are also important. This spatial awareness is used, for example, when switching attention from one person to another during a meeting or a dinner conversation. It also plays a major role when trying to understand what someone is saying in a very reverberant room. These aspects of hearing have to be taken into account to ensure that hearing aids maintain the full richness of the acoustical information available to listeners and to help them extract meaning from it. Therefore, there is a need to develop and test future hearing aids in a variety of real-life sound environments. Recent developments in room acoustics modeling and sound reproduction have made it possible to create complex listening situations in the laboratory by creating a so-called virtual sound environment (VSE). 1,2 In a VSE, sound scenes are constructed in a computer by modeling sound sources in a simulated (or virtual) room. The sound of these virtual sources is then played through a large array of loudspeakers. A VSE can include many virtual sound sources around the listening position (in different directions and at different distances), and the dimensions and wall properties of the room can be changed. When placed in the middle of the loudspeaker array, the listener perceives all attributes of the sound as in a real physical environment. Thus, the listener can be “transported” to different listening environments, bridging the gap between the laboratory and real life. Oticon recently constructed a VSE system at its head office in Denmark. The physical setup consists of 29 loudspeakers placed on a sphere around the listening position in a sound studio (see Figure 1). Many listening tests can be performed in this VSE system to gain insights into the perception of speech in complex acoustic environments. It also opens up the possibility of studying many other aspects of sound, such as sound localization, reverberation, and masking phenomena. The system allows for testing new advancements in hearing aid technology directly on users early in the development process. Thus, the needs of users can be clarified and the benefit of the hearing aids maximized.