154th ASA Meeting, New Orleans, LA

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Internet Acoustics and "Plucking the Internet"

Chris Chafe- cc@ccrma.stanford.edu

Center for Computer Research in Music and Acoustics, Stanford University
Stanford, CA 94305

Popular version of paper 4pMU5
Presented Friday afternoon, November 30, 2006
154th ASA Meeting, New Orleans, LA

We use sounds to learn about the state of our environment and objects in it. Just like in air, sound waves traveling across the Internet can bounce off edges, boundaries and obstacles. These reflections give rise to a configurable sound world of rooms with enclosing walls and other kinds of objects which can vibrate. This world is entered from anywhere in the physical world connecting with a high-enough speed Internet connection. The presentation will describe how music ensembles at Stanford and elsewhere are now coming together and making music in these Internet music halls, and how the relatively short time delays of the Internet can be used to constitute a new breed of synthetic, distributed musical instruments. Short-enough echoes (for example, between West Coast sites) are used to create instrument tones whose pitches are in the musical range. One can actually "play the network" as a guitar or flute stretching between San Francisco and Los Angeles. One application uses these tones to display the quality of the intervening Internet path.

Musicians and network engineers are probing the qualities of this new acoustical medium. Our group at Stanford creates "Sound waves on the Internet from real-time echoes" (SoundWIRE) by using special-purpose software. Employing Internet2 for reliable high-speed streaming, we can create network auditoriums with realistic room-like echoes. Musicians separated by a continent can enter the same acoustical space and rehearse together for jam sessions and concerts. Audio conferencing in these "acoustical chat rooms" achieves a sense of co-location and presence not possible in traditional teleconferencing.

Sound transmission in the medium has its differences from how sound propagates in air (which is itself different from how sound travels in water, through the earth or along stretched strings). The most unusual aspect is the slight non-uniformity of sound travel speed. Synthetically created rooms have slightly changing dimensions as a result, since the timing and symmetry of echoes depends on the speed of sound inside the room.

The SoundWIRE technique provides a means to gain an impression of the solidity of Internet connections. Just as someone might clap to get a sense of the size of a darkened room or knock on an object to know its rigidity, network users can tap on their Internet connections and listen to the vibrations that result. By plucking a "network guitar," the quality of service (QoS) becomes apparent. Using physical model synthesis we imitate a guitar string whose pitch is a function of the round-trip time of the network path between two sites. The longer the sound takes to make it back, the lower the resulting pitch. And the more constant the tone, the better the QoS and the closer it is to ideal. Because the speed of sound is non-uniform, the pitch of these synthetic instruments may have a wavering vibrato which is easily heard without musical training. An audio "ping" in this form serves as a kind of Internet SONAR to detect problems in real time.

The acoustics of the Internet has a number of other characteristics which will be described in the presentation. The analogy that comes closest is from underwater acoustics. Entering into these different sound worlds with our ears, the properties of water and Internet media give them a sonic imprint all their own. We know very well the sound of the former and may soon become familiar with the latter.

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