Absolute hearing threshold (ATH) is the minimum sound level of a pure tone that the average human ear with normal hearing can hear without the presence of another voice. The absolute threshold is related to sounds that only organisms can hear. The absolute threshold is not a discrete point, and is therefore classed as the point at which the sound generates a certain percentage response of time. This is also known as the threshold of hearing.
The auditory threshold is generally reported as a 20 micropascal RMS sound pressure, corresponding to the sound intensity of 0.98 pW/m 2 at 1 atmosphere and 25 Ã, Â ° C. This is approximately the quietest sound of a young child with undamaged hearing can detect at 1,000 Hz. The auditory threshold depends on the frequency and it has been shown that ear sensitivity is best at frequencies between 2 kHz and 5 kHz, where the threshold reaches as low as -9 dB SPL.
Video Absolute threshold of hearing
Metode psikofisik untuk mengukur ambang
The measurement of the absolute hearing threshold provides some basic information about our hearing system. The tools used to gather such information are called psychophysical methods. Through this, the perception of our physical stimulus (sound) and our psychological response to sound is measured.
Some psychophysical methods can measure absolute thresholds. It varies, but certain aspects are identical. First, the tests define the stimulus and determine the way in which the subject should respond. The test presents the voice to the listener and manipulates the stimulus level in a predetermined pattern. The absolute threshold is defined statistically, often as the average of all auditory thresholds obtained.
Some procedures use a series of trials, with each experiment using a 'single interval' yes'/"no" paradigm.This means that the sound can be present or absent in a single interval, and the listener must say whether he thinks the stimulus is there. does not contain any stimulus, it's called a "trial."
Classic method
Two intervals are presented to the listener, one with a tone and one without tone. The listener must decide which interval has the tone in it. The number of intervals can be increased, but this can cause problems for the listener to remember which interval contains the tone.
Adaptive methods
In contrast to the classical method, where the pattern for altering stimuli is preset, in adaptive methods the subject's response to previous stimuli determines the rate at which the next stimulus is presented.
A simple '1-down-1-up' method consists of a series of up and down and reversal trials (reversal). The stimulus rate increases if the subject does not respond and decreases when the response occurs.
- Similarly, as in the boundary method, the stimuli are adjusted in a given step. After obtaining six to eight reversals, the first is discarded and the threshold is defined as the mean midpoint of the rest of the run. Experiments show that this method only gives 50% accuracy.
- To produce more accurate results, this simple method can be further modified by increasing step size in the descending process, e.g. 'Method 2-down-1-up', '3-down-1-up'.
Tracking method Bekesy
The Bekesi method contains several aspects of classical methods and ladder methods. The stimulus rate automatically varies at a fixed rate. Subjects are required to press a button when a stimulus is detected.
- After the button is pressed, the level is automatically lowered by the motor-driven attenuator and increases when the button is not pressed. The threshold is tracked by the listener, and is calculated as the mean of the midpoint of the run as recorded by the automaton.
Maps Absolute threshold of hearing
Hysteresis effect
Hysteresis can be defined roughly as 'lagging of a effect behind the cause'. When measuring the threshold of hearing, it is always easier for the subject to follow the audible tone and decrease the amplitude than to detect a previously unheard tone.
This is because a 'top-down' effect means that subjects expect to hear sound and, therefore, are more motivated with higher concentration levels.
The 'bottom-up' theory explains that unwanted externals (from the environment) and internal noise (eg heartbeat) on the subject respond only to sounds if the signal to noise ratio is above a certain point.
In practice this means that when measuring the threshold with noise decreases in amplitude, the point at which the sound becomes inaudible is always lower than the point where it returns to the audibility. This phenomenon is known as 'hysteresis effect'.
Psychometric function of absolute hearing threshold
The psychometric function 'represents the likelihood of a particular listener's response as a function of the magnitude of certain sound characteristics being studied'.
To give an example, this could be the probability curve of a subject that detects the sound presented as a function of the sound level. When the stimulus is presented to the listener, one will hope that the sound will be audible or inaudible, resulting in a 'doorstep' function. In reality there is a gray area where listeners are not sure if they really hear a sound or not, so their responses are inconsistent, resulting in a psychometric function.
Psychometric function is a sigmoid function characterized by its shape in its graphical representation.
Minimum audible field (MAF) vs. minimum pressure can be heard (MAP)
Two methods can be used to measure the minimal stimulus that can be heard and therefore the absolute hearing threshold. Fields that can be heard at least involve the subject sitting in the field of sound and the stimulus presented through the loudspeaker. The sound level is then measured at the head of the subject with the subject not in the sound field. Minimal audible pressure involves providing stimulation through headphones or earphones and measuring sound pressure in the subject's ear canals using a very small probe microphone. Two different methods produce different thresholds and the audible field threshold is often often 6 to 10 dB better than the minimal sound pressure threshold. It is estimated that this difference is due to:
- monaural vs binaural hearing. With a minimal audible field, both ears are capable of detecting stimuli but with minimal sound pressure only one ear is capable of detecting stimuli. Binaural hearing is more sensitive than monaural hearing/
- Physiological sounds are heard when the ear is clogged by earphones during the audible minimum pressure measurement. When the ears are closed, the subject hears a body sound, like a heartbeat, and this may have a masking effect.
Minimal hearing areas and minimal sound pressure are important when considering calibration issues and they also illustrate that human hearing is most sensitive in the 2-5 kHz range.
Temporary addition
The temporal summation is the relationship between the duration of the stimulus and the intensity when the presentation time is less than 1 second. Hearing sensitivity changes when the sound duration becomes less than 1 second. The threshold intensity decreases by about 10 dB when the duration of the tone explosion increases from 20 to 200 ms.
For example, suppose that the quietest sound the subject can hear is 16 dB SPL if sound is presented at 200 ms. If the same sound is then presented for a duration of only 20 ms, the quietest sound that the subject can now hear rises up to 26 dB SPL. In other words, if the signal is shortened by a factor of 10 then the signal level must be increased by 10dB to be heard by the subject.
The ear operates as an energy detector that shows the amount of energy that exists within a given time range. A certain amount of energy is required within a period of time to reach the threshold. This can be done using higher intensity for less time or by using lower intensity for more time. The sensitivity to sound increases with increasing signal duration to about 200 to 300 ms, after which the threshold remains constant.
The ear timpani operate more as a sound pressure sensor. Also the microphone works the same way and is insensitive to the sound intensity.
See also
- dB (A)
- Contour loudness
- Hearing range
- Loudness
- Phon
- Psychoacoustics
- Psychophysics
- The signal detection theory
- Sone
References
- Fechner, G., 1860. Psychophysical elements . New York: Holt, Rinehart, and Winston. Excerpts from the book are available at: http://psychclassics.yorku.ca/Fechner/.
- Katz J. (Ed). United States: Lippencott, Williams & amp; Wilkins
- Levitt H., 1971. "Changing up-down methods in psychoacoustics". J. Acoust. Soc. Amer. 49, 467-477. Available for download from: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JASMAN00004900002B000467000001&idtype=cvips&gifs=yes. (Retrieved 1 March 2007).
- www.thefreedictionary.com. Retrieved 28 February 2007
External links
- Comparison of threshold estimation methods for children ages 6-11 years
- Comprehensive Audiology Vocabulary and related topics
- The fundamental aspect of listening
- Lighter contours and the same audiometry - Your own auditory test
- Hearing Threshold Online Test - Alternative audiometric test, with calibrated levels and results expressed in dBHL
- Psychoacoustics basics
- Minimizes boredom by maximizing efficient possibilities from masked thresholds
- In Minimum Sound Sound Fields
- Psychometric Functions for Noise Detection on Noise in Children
- Psychophysical methods
- The reference level for objective audiometry
- Responsive bias in psychophysics
- Human Ear Sensitivity
- Psychoacoustics from multichannel audio
- Three Models of Temporal Summation are Evaluated Using Subjects Hearing Normal Hearing Loss and Hearing Loss
- Threshold
- Threshold Threshold - equations and graphics
Source of the article : Wikipedia
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