Material culture refers to the touchable, material 'things'--physical objects that can be seen, held, felt, used--that a culture produces. Examining a culture's tools and technology can tell us about the group's history and way of life. Similarly, research into the material culture of music can help us to understand the music-culture. The most vivid body of 'things' in it, of course, are musical instruments. We cannot hear for ourselves the actual sound of any musical performance before the 1870s when the phonograph (留声机) was invented, so we rely on instruments for important information about music-cultures in the remote past and their development. Here we have two kinds of evidence: instruments well preserved and instruments pictured in art. Through the study of instruments, as well as paintings, written documents, and so on, we can explore the movement of music from the Near East to China over a thousand years ago, or we can outline the spread of Near Eastern influence to Europe that resulted in the development of most of the instruments in the symphony orchestra. Sheet music or printed music, too, is material culture. Scholars once defined folk music-cultures as those in which people learn and sing music by ear rather than from print, but research shows mutual influence among oral and written sources during the past few centuries in Europe, Britain, and America, Printed versions limit variety because they tend to standardize any song, yet they stimulate people to create new and different songs. Besides, the ability to read music notation (乐谱) has a far-reaching effect on musicians and, when it becomes widespread, on the music-culture as a whole. One more important part of music's material culture should be singled out: the influence of the electronic media--radio, record player, tape recorder, television, and videocassette recorder, with the future promising talking and singing computers and other developments. This is all part of the 'information revolution'', a twentieth-century phenomenon as important as the industrial revolution was in the nineteenth. These electronic media are not just limited to modern nations, they have affected music-cultures all over the globe. Research into the material culture of a nation is of great importance because ______.