Hearing and other senses
Sound Sound: sensed variations in air pressure Frequency: number of peaks that pass a point per second (Hz) Pitch 2
Some Sound and Hearing Links Useful (and moderately entertaining) websites: Online Tone Generator: http://onlinetonegenerator.com/ AudioNotch tone generator: https://www.audionotch.com/app/tune/ Szynalski's tone generator http://www.szynalski.com/tone-generator/ White (and other) noise generator: https://mynoise.net/noisemachines/whitenoisegenerator.php 3
Sound Measurement Range: p < 0.001 bar (normal breathing) p > 1000 bar (jet plane) 4
Sound Pressure Level (SPL) SPL = L p = 20 log 10 ( p/p r ) p = RMS sound pressure of target sound p r = RMS sound pressure of reference sound (e.g. 0.0002 bar) SPL units: decibels (db) 5
Sound Measurement Devices The device on the left is a sound level meter and is primarily used for noise abatement activities and acoustical work such as determining noise control criteria for an occupancy or for ambient noise analysis and control. The device in the center is a sound level meter/noise dosimeter which accumulates, or logs noise exposure for an entire work shift. This instrument is primarily used for OSHA hearing conservation activities. The device on the right is a previous-generation sound level meter. 6
A, B, and C Scales 7
Anatomy of the Ear Source: Wikimedia Commons, http://upload.wikimedia.org/wikipedia/commons/d/d2/anatomy_of_the_human_ear.svg, accessed 7 October 2010. 8
Hearing Anatomy & Physiology Pinna Auditory Canal Tympanic Membrane Ossicles Malleus (hammer) Incus (anvil) Stapes (stirrup) Ligaments Muscles Amplitude reduction Pressure amplification Attenuation reflex (protection, low frequency masking) Oval Window Cochlea Auditory Nerve Auditory Cortex 9
Cochlea ( unrolled from actual spiral shape) Stapes Oval Window Scala Vestibuli & Scala Media Helicotrema Round Window Scala Tympani Basilar Membrane Organ of corti Hair cells High Frequency Low Frequency 10
Auditory Experience Sound intensity/spl Loudness Frequency Pitch 11
Psychophysical Scaling loudness not directly proportional to intensity psychophysical (perceived loudness) scales Phons Equal loudness contours phons = db @ 1000 Hz Sones Relative subjective loudness 1 sone = 1000 Hz @ 40 db 2 sones = sound judged twice as loud as 1 sone sound 12
Sensitivity Range of Hearing: Highest Sensitivity: 20-20,000 Hz 1,000-3,000 Hz Lowest Detectable Intensity: 0 db 13
Limits 14
Discriminability Ability to distinguish between two simuli (e.g. sounds) Frequency - Pitch Intensity - Loudness Spectrum Phase (?) Just Noticable Difference (JND) Least change in a stimulus or the least difference between two stimuli that can be detected 50 % of time. 15
Absolute Discrimination Dimension (s) # of Levels Intensity 4-5 Frequency 4-7 Duration 2-3 Intensity & Frequency 9 16
Masking Sound A (masking sound) reduces sensitivity of ear to Sound B (masked sound). Raised threshold for B (masked threshold). 17
Masking by Pure Tones Explanation: A pure 1,000 Hz tone @ 30 db would be masked by a pure 200 Hz tone @ 60dB, but not by a pure 200 Hz tone @ 40 db and not by a pure 3,500 Hz tone even at 60 db. 18
Masking by Wideband Noise 19
Reducing Masking Signal Control Selection - distinction from noise Intensity - above masked threshold Noise Control Selection - distinct from signal Intensity - reduce Filter - alter spectrum to reduce masking 20
Alarms Rationale for auditory alarms sound omnidirectional can t close our ears Criteria for auditory alarms must be above background sound must not be above danger level should not be overly startling (longer rise time) should not interfere with other signals should be informative 21
Designing Auditory Alarms do task analysis stay within limits of absolute judgment capitalize on the dimensions pitch envelope rhythm timbre design sound specifics 22
False Alarms false alarms loss of trust disabling of alarms missed signals 23
Speech Issues Example: Tenerife Collision of two B-747s 27 Mar 1977 583 killed) bottom-up issues Language, accents Radio quality Squeal from simultaneous transmissions Non-standard terminology top-down issues KLM captain's expectations 24
Masking Effects female voice more vulnerable consonant sounds (esp. s, ch) more susceptible to masking than vowels climb to vs climb through 25
Measuring Speech Communication Bottom-Up: Articulation Index (AI) signal-to-noise ratio speech db / noise db weighted across frequency bands Top-Down: Speech Intelligibility Level (SIL) % items correctly heard 26
Speech Distortions Examples clipping (beginnings, ends of words) reduced bandwidth echoes reverberations low quality synthesized speech 27
Temporary Hearing Loss Continuous noise leads to hearing loss Temporary threshold shift at 2 min (TTS2 ) 70-75 dba : no TTS 2 80-105 dba: TTS 2 proportional to exposure 28
Performance vs. Safety: Permanent Hearing Loss Continuous noise may lead to permanent hearing loss Begins at 4000 Hz Generally restricted to 3000-6000 Hz 29
Hearing Loss 30
Noise - Induced Hearing Loss 31
OSHA Standards: Continuous Noise 32
OSHA Standards: Impulse Noise 33
Noise Dosage total (daily) dose = sum of partial doses Requirement: total dose < 1.00 34
Example Worker exposed to 90 dba for 4 hours, 105 dba for 30 minutes. Within dosage limits? 4 hr @ 90 dba = 4 / 8 = 0.5 0.5 hr @ 105 dba = 0.5 / 1 = 0.5 Total dosage = 0.5 + 0.5 = 1.0 Since 1.0 < 1.0, dosage is OK 35
Noise Control Source Path Receiver Design Barriers Ear plugs Maintenance Enclosures Ear muffs Mountings Baffles Mufflers 36
Hearing Protectors 37
Human Senses and the Energies That Stimulate Them Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering, New York: Wiley, 212. Sensation Sense Organ Stimulation Origin Sight (vision) Eye Some electromagnetic radiation External Hearing (audition) Ear Pressure variations External Rotation Semicircular canals Muscle receptors Fluid movement in inner ear Muscle stretching Internal Internal Falling, rectilinear movement Otoliths Position change of otoliths in inner ear Internal Taste Specialized cells in tongue & mouth Some chemical substances External on contact Smell Specialized cells in nasal cavity Some vaporized chemical substances external 38
Human Senses and the Energies That Stimulate Them Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering, New York: Wiley, 212. Sensation Sense Organ Stimulation Origin Touch Skin Surface deformation On contact Pressure Skin & underlying tissue Temperature Pain Position & movement (kinesthesis) Skin & underlying tissue Free nerve endings (?) Nerve endings in muscle, tendons, joints Temperature change, friction, chemicals Pressure, heat, cold, shock, chemicals Muscle stretching, contraction, joint movement External on contact Internal or external on contact Internal Mechanical vibration No specific organ Variations of skin pressure External on contact 39