THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

19.5 Portable Audio Playback Equipment 581Institute of Digital Media in Germany who is known as the “father of MP3 describedin the next section, developed a spatial sound technology called Iosono r○ .It is intended to carry sound reproduction beyond the 5.1- and 7.1-channel systemsand is based on the principle that sound waves can be reproduced using secondarysources at the perimeter of the original sound field. This process is called wavefield synthesis (WFS).In the Iosono system, speaker arrays ring the listening area and function in acoordinated, phased fashion to reproduce each individual sound wave. An exampleof an acoustical illusion that can be created is that of a helicopter that slowlyapproaches the audience, flies through the middle of the theater, and disappearsinto the distance. The audience hears the helicopter noise that would be generatedif the helicopter were actually flying this path. It is also claimed for this system,aimed at cinemas and eventually the home theater, that the whole room can act asa listening “sweet spot.”An Iosono system consists of a continuous ring of speakers configured in panelsof 8 two-way speakers, mounted on the peripheral walls of the space and connectedvia fiber-optic cables to a central Iosono processing unit. The number of speakerpanels used depends on the size of the space. In February 2003, a 100-seat movietheater in Ilmenau, Germany, received the first commercial Iosono Cinema system.The installation used 198 speaker systems. Because of the fact that commercialmovie sound has yet to be mixed, the Iosono system is also capable of playback ofother formats, such as 5.1, DTS, SDDS as well as stereo. However, the audiencenoticed the enlargement of “sweet spot” and was treated to a 90-s trailer thatdemonstrated the effect of a full Iosono system.19.5 Portable Audio Playback EquipmentIn this section reference is made to handheld devices, not to playback units thatare transportable but too large to be held conveniently. The first units of this typewas the Sony Walkman r○ , a cassette player, which was to be joined by competingmodels, and subsequently the Sony Discman r○ that played compact disks. Thenewer units we describe here can download music from the Internet as well asfrom other sources and the storage is usually done on rewriteable nonvolatilememories.MP3MP3, developed by Germany’s Frauenhofer research institute, denotes MPEGAudio Layer 3. It is an audio compression technology that constitutes part of theMPEG-1 and MPEG-2 specifications. The company Thomson Media patented thistechnology in the United States and in Germany.Uncompressed audio, such as that found on audio compact disks store moredata than human hearing can process. Music on CDs has a bandwidth of 1.4 MB/s.This means that 1 min of music on a CD takes up to 10 MB of data. Through the