Hearing and other senses Sound Sound: sensed variations in air - - PowerPoint PPT Presentation

Hearing

and other senses

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Sound

• Sound: sensed variations in air pressure
• Frequency: number of peaks that pass a point per

second (Hz)

• Pitch

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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

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Sound Measurement

• Range: p < 0.001 bar (normal breathing)

p > 1000 bar (jet plane)

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Sound Pressure Level (SPL)

SPL = Lp = 20 log10 ( p/pr)

p = RMS sound pressure of target sound pr = RMS sound pressure of reference sound (e.g. 0.0002 bar) SPL units: decibels (dB)

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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

• n the right is a previous-generation sound

level meter.

Sound Measurement Devices

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A, B, and C Scales

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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.

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Hearing Anatomy & Physiology

Pinna Auditory Canal Tympanic Membrane Ossicles Oval Window Cochlea Auditory Nerve Auditory Cortex Malleus (hammer) Incus (anvil) Stapes (stirrup) Ligaments Muscles Amplitude reduction Pressure amplification Attenuation reflex (protection, low frequency masking)

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Cochlea

(“unrolled” from actual spiral shape)

Stapes Round Window Oval Window Scala Vestibuli & Scala Media Scala Tympani Basilar Membrane Organ of corti Hair cells Helicotrema High Frequency Low Frequency

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Auditory Experience

• Sound intensity/SPL  Loudness
• Frequency  Pitch

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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

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Sensitivity

Range of Hearing: 20 - 20,000 Hz Highest Sensitivity: 1,000 - 3,000 Hz Lowest Detectable Intensity: 0 dB

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Limits

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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.

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Absolute Discrimination

Dimension (s) # of Levels Intensity 4 - 5 Frequency 4 - 7 Duration 2 - 3 Intensity & Frequency 9

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Masking

• Sound A (masking sound) reduces

sensitivity of ear to Sound B (masked sound).

• Raised threshold for B (masked

threshold).

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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.

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Masking by Wideband Noise

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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

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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

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Designing Auditory Alarms

• do task analysis
• stay within limits of absolute judgment
• capitalize on the dimensions

– pitch – envelope – rhythm – timbre – design sound specifics

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False Alarms

• false alarms 

– loss of trust – disabling of alarms – missed signals

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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

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Masking Effects

• female voice more vulnerable
• consonant sounds (esp. s, ch) more

susceptible to masking than vowels

• “climb to” vs “climb through”

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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

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Speech Distortions

• Examples

– clipping (beginnings, ends of words) – reduced bandwidth – echoes – reverberations – low quality synthesized speech

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Temporary Hearing Loss

• Continuous noise leads to hearing loss
• Temporary threshold shift at 2 min (TTS2)

– 70 - 75 dBA : no TTS2 – 80 - 105 dBA: TTS2 proportional to exposure

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Performance vs. Safety: Permanent Hearing Loss

• Continuous noise may lead to permanent

hearing loss

• Begins at 4000 Hz
• Generally restricted to 3000 - 6000 Hz

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Hearing Loss

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Noise - Induced Hearing Loss

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OSHA Standards: Continuous Noise

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OSHA Standards: Impulse Noise

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Noise Dosage

• total (daily) dose = sum of partial doses
• Requirement: total dose < 1.00

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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

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Noise Control

Source Path Receiver Design

Barriers Ear plugs

Maintenance Enclosures

Ear muffs Mountings Baffles Mufflers

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Hearing Protectors

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Human Senses and the Energies That Stimulate Them

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

Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering, New York: Wiley, 212.

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Human Senses and the Energies That Stimulate Them

Sensation Sense Organ Stimulation Origin Touch Pressure Skin Skin & underlying tissue Surface deformation On contact Temperature Skin & underlying tissue Temperature change, friction, chemicals External on contact Pain Free nerve endings (?) Pressure, heat, cold, shock, chemicals Internal or external on contact Position & movement (kinesthesis) Nerve endings in muscle, tendons, joints Muscle stretching, contraction, joint movement Internal Mechanical vibration No specific organ Variations of skin pressure External on contact

Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering, New York: Wiley, 212.