The Virtual Geiger-Counter is an interactive sonification designed for the VRGeo research consortium on Virtual Reality for Oil and Gas exploration [Barrass and Zehner, 2000]. The Geiger counter sound is familiar to most seismic interpreters who recognize the way the clicking varies with changes in radiation. One of the expert interpreters used this sonification to confirm expected changes in radiation in the 3D visualization of geological strata. The interpreters were also interested in the way that other variables, such as porosity, chemicals, and conductance vary at the same time. In short trials over a series of meetings the interpreters quickly understood the extension of the Virtual Geiger counter to other variables. The need to understand relative changes led to the suggestion to sonify more than one variable at the same time. In the next version the generic clicking noise was replaced with timbre samples that segregated at intertone onset intervals (IOI) of 200 ms when played in a Van Noorden gallop. This stream segregation increases at faster rates of clicking caused by higher levels of radiation and other variables. The data values were then used to control a filter that affected the spectral centroid of the timbre grains. Uncorrelated variables produce two distinctly separate Geiger counter streams with different timbres. Correlated values merge to produce a single Geiger stream with increased clicking density. This dynamic merging from two to one stream based on the relations in the data is significant because it distinguishes stream-based sonification from conventional channel-based sonifications that assume perceptual independence between auditory channels.
Further questions for empirical study arising from this case study relate to the accuracy of judgments with the Virtual Geiger-counter: How does it compare with visual scatterplots ? Can relations between more than two variables be understood in this way?
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