Transcript Alarms
Chapter 5 Sound Intensity (db) = 20 log (P1/P2) Loudness (intensity) Pitch (frequency) Perceived Location Quality (set of frequencies and envelop) Timbre – what determines the sound of a trumpet from a flute Sounds can be masked by other sounds Principles of masking: The minimum intensity difference to make sure that a sound can be heard is around 15db above the mask Sounds tend to be masked most by sounds in a critical frequency band surrounding the sound that is being masked Low-pitch sounds mask high-pitch sounds more than the converse. e.g., a woman’s voice is more likely to be masked by other male voices than other female voices masking a man’s voice even if both are speaking at the same intensity Alarms are normally auditory because hearing is omnidirectional and it is much easier to close our eyes than our ears However auditory alarms have there drawbacks when not properly designed Must be heard above background noise Intensity should not be above the danger level for hearing when possible The alarm should not be over startling The alarm should not disrupt other the processing of other signals or other background speech communications Alarm should be informative to the listener on what action to take – fire alarm to cause building evacuation based on previous knowledge Perform environmental & task analysis to understand quality & intensity of other sounds (noise or communications) Try to stay within the limits of absolute judgments Design warning structure/rational To avoid confusion consider voice alarms – two concerns are masking by other voice communications and language of listener Make redundant with auditory alarm Consider consequences of missing a true warning condition versus a false alarm Too many false alarms can cause lack of appropriate response Try to improve sensitivity of alarm system Train users to inevitability of false alarms, but to always respond as if it were true Install multi-level alarm system – e.g., weather warning Speech Spectrograph Masking Effects of Noise: Potential for masking dependent intensity and frequency of the noise Potential Health Hazard Potential Environmental Irritant Loss of sensitivity while noise is present Permanent hearing loss Temporary threshold shift Signal Enhancement Noise Reduction The source: equipment and tool selection The environment The listener: ear protection Environmental Noise Is all noise bad? No (background music to mask irritating ticking or conversation distractions) Touch: touch (pressure) and haptic (shape) senses Problems – surface membranes, gloves, shapes, spatial/symbolic information, & virtual environments Proprioception (brain’s knowledge of finger position) & Kinesthesis (brain’s knowledge of joint motion) Three semicircular canals act like three gyros in early navigation systems