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 draw- backs 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