The relationship between physical acoustic parameters and the subjective responses they evoke is important to assess in audio alarm design. While the perception of urgency has been thoroughly investigated, the perception of other variables such as pleasantness, negativeness and irritability has not. To characterize the psychological correlates of variables such as frequency, speed, rhythm and onset, twenty-six participants evaluated fifty-four audio warning signals according to six different semantic differential scales. Regression analysis showed that speed predicted mostly the perception of urgency, preoccupation and negativity; frequency predicted the perception of pleasantness and irritability; and rhythm affected the perception of urgency. No correlation was found with onset and offset times. These findings are important to human-centred design recommendations for auditory warning signals.

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An audio-guide prototype was developed which makes it possible to associate virtual sound sources to tourist route focal points. An augmented reality effect is created, as the (virtual) audio content presented through headphones seems to originate from the specified (real) points. A route management application allows specification of source positions (GPS coordinates), audio content (monophonic files) and route points where playback should be triggered. The binaural spatialisation effects depend on user pose relative to the focal points: position is detected by a GPS receiver; for head-tracking, an IMU is attached to the headphone strap. The main application, developed in C++, streams the audio content through a real-time auralisation engine. HRTF filters are selected according to the azimuth and elevation of the path from the virtual source, continuously updated based on user pose. Preliminary tests carried out with ten subjects confirmed the ability to provide the desired audio spatialisation effects and identified position detection accuracy as the main aspect to be improved in the future.

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