Foundations of Audiology Flashcards
Intensity
Influenced by magnitude of the sound and the medium in which it is transmitted (has an absolute magnitude)
BEL
Sound intensity measured in pressure of pascals
A force measured in Newtons (N) applied over an area (m2)
A Bel is a ratio
Decibel
The logarithm involving a power of 10 of the sound intensity as a multiple of the threshold sound intensitiy
Refers to intensity of a sound relative to the just noticable difference of a sound detection
Periodic signals
repeats pattern of vibration indefinitely (sinusoids-pure tones)
Aperiodic signal
Do not repeat in time These include: Noise Gaussian Noise Uniform Noise
Noise
Contains energy at every frequency over a specific range
Gaussian Noise
Amplitudes distributed normally
White noise: energy present as continuous function of frequency
Narrow band noise: contain energy only at the frequencies surrounding the test signal (speech noise: centered at 300-3000 Hz)
Uniform Noise
Amplitudes all the same
Pink Noise: energy present as continuous function of frequency
Relative amplitude is decreased 3dB/octave as frequency increases
Emphasizes low frequency energy
Phase
A pattern of activity (voltage or pressure changes over time) that repeats with every cycle 360 degrees.
Frequency of the signal is in cycles per second or Hz
Modulation: when sinusoids are added together, perceptible fluctuations may be noted in the amplitude, especially if the sinusoids are different frequencies (FM=frequency modulations)
Wavelength
Sound propagated through space over time and distance
Lower frequencies-larger wavelength so tend to go around objects in their path
Higher frequencies-smaller wavelengths tend to bounce off objects in their path
Inverse Square Law
As the distance increases, the intensity of the sound decreases proportionally (by approx. 1/2 when the distance is doubled). Halving the SPL results in a drop of 6 dB SPL, so a SPL of half of 30 dB SPL is 24 dB SPL
Dependent on room conditions: reverberant room- sound may not decrease at all b/c reflective sounds will add with directed sounds
Dead room: sound may dampen rapidly
Smallest pressure detected by the human ear at 1000 Hz
10^ -16watts/cm^2 or ^-12watts/m^2
Largest pressure: 1 watt/m^2
Psychoacoustics
Identifying gradual changes in perception
Threshold
Value between where signal detection is not possible and above where signal is detected 100% of the time (between 10-15dB variable range). Target of 50% correct.
Signal Detection Theory
Identifying when a signal is present
Minimize false alarm rate
Reinstruction
Retraining
Present signal at a louder intensity so the person is sure of what they are listening for
Present a variation of the signal for easier detection (pulsed, FM, narrow band-often 10dB louder than pure tone)
Methods to collect detection/discrimination data
Method of limits-tester controlled
Method of adjustment- listener controlled
Method of constant stimuli
Scaling
Acoustics vs Psychoacoustic
Intensity = Loudness Frequency = Pitch
Frequency Resolution
Sharp and full of detail
Temporal resolution
Detection of small changes in temporal envelope
Audiometers described in terms of
Signal-Pure tone/speech
Frequency range-Limited to extended high frequency
Method of Measurement-Manual to computer control
Purpose: Screening/Diagnostic/Clinical/Industrial
Number of independent channels
Portable
Free Field
Transducer Types
Supra-aural earphones: flat freq response with limited output above 8kHz Insert earphones: 12mm length Circumaural earphones Loudspeakers Bone Vibrators- B-71, B-72, KH-70
Calibration tools
Couplers, Sound level meter, Voltmeter, Electronic counter/timer, Oscilloscope
Parameters: Output levels, attenuator linearity, freq accuracy, harmonic distortion, signal switching, masking, unwanted noise, monitoring meters for speech, playback devices, ambient noise levels
