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Fig. 6. St. Margaret’s Church, East Wellow, Hampshire, United Kingdom is an early 13th Century building with earlier foundations. The grave of Florence Nightingale can be seen in the foreground.
compensate for sound speed changes within the vocal tract while properly amending the larynx vibration frequency for fluid loading. For interest, the calculated result if the fluid loading stage is neglected is also included in the media files.
The sound files are based on the assumption that they are recorded using a microphone that has the same perform- ance characteristics on each planet as had the microphone used on Earth. Fluid loading and external conditions (pres- sure, temperature, etc.) would of course have to be taken into account in the design of the instrument, which includes use of the principles outlined in this paper (the same principles could of course be applied to examine to what extent the ear would be compromised, although we have some experience from this from tests of hearing underwater with and without
the intensity of the voice tracks cannot. While the predictions for the music tracks (involving as they do an inanimate organs and microphones) are meaningful with respect to the interpretation of future extraterrestrial signals in terms of source characteristics, and to the design of future micro- phones (for probes or helmets), the range of human factors involved in generating speech in alien environments means that the voice tracks are purely illustrative.
Conclusions
The purposes for which predictions have been made of the sounds of music are not grounded in the physical trans- position of an Earth-tuned organ to another world: organs are constructed very much for the specific location they will occupy, and tuned appropriately (for example, the reed will be tuned to the pipe, and not vice versa). However the exer- cise quantitatively illustrated the range of both physical and subjective ways in which the alien world affects sound pro- duction and propagation. The modeling of sound on other worlds can inform the design of future acoustic sensors, and affirm our ability to predict, analyze, and interpret extrater- restrial acoustic phenomena accurately, whether that inter- pretation takes the form of the subjective recognition of thunder, a splashdown, wind or seismic activity, or whether it encompasses a full quantitative inversion.
With specific application to music, the effect of the alien world is dependent on the mechanism by which the sound is generated. The effect depends very much on the instrument and the environment—the example of flue and reed pipes being affected differently by the gas was given (not forgetting other factors: for example some reeds rely on gravity to sup- ply the restoring force, while others do not). Indeed, changes of gas could be used to test the importance of components and their interactions in those instruments, where complex
an air bubble trapped in the ear). Furthermore, it is assumed that the organs have the same source level (intensity at the position of the organist). The actual source level consideration is more complicated than this, as such organ pipes are designed to speak when excited by a given pressure difference. Hence the source intensity considerations are not simply one of scaling but, as with many instruments, also incorporates
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thresholding effects.
The organ pipes are assumed to
act as flue pipes and the end-correc- tions in the pipe are negligible. For the voice tracks, the same assump- tion carries through the processing to imply that the acoustic intensity of the voice at the microphone, 1 m from the speaker, is constant, which is unrealistic. As such, while the intensity of the music tracks can be compared with the calibration tone that is provided with the audio files,
Fig. 7. The organ.
Sounds in Space 23