What is the absolute threshold of hearing?

The threshold of hearing is the Sound pressure level SPL of 20 µPa (micropascals) = 2 × 10−5 pascal (Pa). This low threshold of amplitude (strength or sound pressure level) is frequency dependent. See the frequency curve in Fig. 2 below

The absolute threshold of hearing (ATH) is the minimum amplitude (level or strength) of a pure tone that the average ear with normal hearing can hear in a noiseless environment.

The threshold of pain is the SPL beyond which sound becomes unbearable for a human listener. This threshold varies only slightly with frequency. Prolonged exposure to sound pressure levels in excess of the threshold of pain can cause physical damage, potentially leading to hearing impairment.

Different values for the threshold of pain:

Threshold of painSPLsound pressure120 dBSPL20 Pa130 dBSPL63 Pa134 dBSPL100 Pa137.5 dBSPL150 Pa140 dBSPL200 Pa

The Threshold of hearing is frequency dependent, and typically shows a minimum (indicating the ear's maximum sensitivity) at frequencies between 1 kHz and 5 kHz. A typical ATH curve is pictured in Fig. 1. The absolute threshold of hearing represents the lowest curve amongst the set of equal-loudness contours, with the highest curve representing the threshold of pain.

In psychoacoustic audio compression, the ATH is used, often in combination with masking curves, to calculate which spectral components are inaudible and may thus be ignored in the coding process; any part of an audio spectrum which has an amplitude (level or strength) below the ATH may be removed from an audio signal without any audible change to the signal.

The ATH curve rises with age as the human ear becomes more insensitive to sound, with the greatest changes occurring at frequencies higher than 2 kHz. Curves for subjects of various age groups are illustrated in Fig. 2. The data is from the United States Occupational Health and Environment Control, Standard Number:1910.95 App F

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The simplest property to exploit is the ATH (Absolute Threshold of Hearing). We simply cannot hear sounds which are too weak. The ATH varies a lot with the frequency of the test sound, which can be seen in Fig. 2. The curve is approximated from experiments on a number of subjects (see [1]).

Figure 2: The absolute threshold of hearing. The numbers indicate the age of the test subjects.

What is the absolute threshold of hearing?


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``An Experimental High Fidelity Perceptual Audio Coder'', by Bosse Lincoln, (Final Project, Music 420, Winter '97-'98).
Copyright © 2006-01-03 by Bosse Lincoln
Center for Computer Research in Music and Acoustics (CCRMA),   Stanford University
What is the absolute threshold of hearing?
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The INTENSITY LEVEL where a sound becomes just audible. For a continuous tone of between 2000 and 4000 Hertz, heard by a person with good hearing acuity under laboratory conditions, this is 0.0002 dyne/cm2 SOUND PRESSURE and is given the reference level of 0 dB.

In terms of AMPLITUDE, the EARDRUM moves about 0.000000001 cm, much less than the wavelength of light. If the ear were any more sensitive it would detect the random movements of air molecules. While 0 dB is the reference employed, the threshold of hearing varies considerably with lower and higher frequencies (see graph of EQUAL LOUDNESS CONTOURS or PHON). Also called minimum audible field (MAF).

See: AUDIOGRAM, BONE CONDUCTION HEARING LEVEL, DECIBEL, DYNAMIC RANGE, HEARING LEVEL, MASKING, SOUND INTENSITY, SOUND PRESSURE LEVEL, THRESHOLD SHIFT. Compare: THRESHOLD OF PAIN, VU METER, ZERO LEVEL VU.

Alternate units for this reference level are: 2 x 10-4 microbar (µbar); 2 x 10-5 Newton/m2 (N/m2); 2 x 10-5 Pascal (Pa); 20 micropascal (µPa).

The hearing threshold is defined as the lowest threshold of acoustic pressure sensation , possible to perceive by an organism. It is a subjective value which may differ individually. The hearing threshold forms the lowest limit of the hearing range ( the highest limit is formed by the threshold of pain). only

Explanation and background information[edit | edit source]

Sound itself is a mechanical wave propagating longitudinally through a medium.

To understand the unit and the value of the hearing threshold we should summarize some important related information :


Sound pressure, or P , refers to pressure variations in a compressible transfer medium (e.g. air), resulting from the propagation of the sound. The sound pressure caused by vibrations is converted in our eardrum into movements of the ossicles and ,after transmission, formed in the inner ear to auditory sensations. It´s unit is Pascal.

So to say it is a force F acting on an area A (our eardrum in this example).

What is the absolute threshold of hearing?

Formula for sound pressure


The lowest value for audible sound pressure is 2·10-5 Pascal.

At this point it is important to remember three facts about the human ear:

1.) Our sensitivity for acoustic sensation can be differentiated by the human being into a scale of 12 values for the sound intensity . For practical use we thus use a logarithmic scale (see also under the point "Phone" downwards)

2.) The human ear is rather a detector for energy transmission , than for sound itself. The signals are converted by special sensory cells in our ear.

3.) The sensitivity of hearing is directly dependent on the frequency .


The Sound level is formed by a sound intensity I , which is related to a fixed and determined Intensity I0 ( = 10-12 W/m2), which causes a barely perceptible sound sensation in the frequency 1000 Hz.

What is the absolute threshold of hearing?

Formula of sound intensity level

The value dB (Decibel) which is seen like a unit. It is though a dimensionless number because she reflects the relation between two (sound) intensities !


What is the absolute threshold of hearing?
Graph of the threhshold of hearing ( compared for different ages)

The more the threshold passes towards lower sound intensity , the more sensitive the ear responds to the corresponding frequency range. In this graph it is seen that the acoustic sensitivity is best at a frequencies of 3 kHz. This is clearly seen in the lowering of the threshold of hearing in "valley" formed by the graph. In this area, only a very low noise level is required to cause a hearing sensation.

For older people, the graph arises more sharply upwards around lowest value ( 0 dB for young, normal hearing people ), so it is necessary to increase the dB for the same frequent tone to hear something. This is why especially for older people or a person with problems of audibleness it is an important value, e.g. to adapt an supportive hearing aid devices.


To simplify things and to connect the sound intensity with the frequency, the unit Phone was introduced, which determined the loudness of a pure tone . It orientates at a fixed frequency of 1000 Hz for different Sound intensities in dB. So for example a tone with the sound intensity of 30 dB is 30 Phon loud.


What is the absolute threshold of hearing?


It is important to mention that the phon value is not proportional to the perceived volume. A sound with 80 phon is not twice as loud as a sound of 40 phon, but 16 times as loud!

Determination of the hearing threshold[edit | edit source]

Methods which are used to determine the individuals hearing threshold are called psychophysical methods. This name derived by the measurement, consisting of a physical signal (the sound) which is perceived by the individual through his sense-organs and changed in his nervous system into a psychological response , which he reflects to the outside by giving e.g. a hand signal to the examiner.

To determine your subjective audible sensitivity it is possible to make an audiogram. This measurement is frequency dependent and gives the test person tones in different loudness levels on a air countucted ear phone, and on a bone conducted ear phone afterwards (bone conductor for comparison with the vibration sensitivity in the ear canal). It is necessary for the examination that the test person is pressing a button in the moment he can perceive the signal to show the examiner/physician that he is able to hear the tone at a certain frequency/sound level.

What is the absolute threshold of hearing?
Example of an audiogram of a normal hearing person

What is the absolute threshold of hearing?
Example for a person who is hearing impaired.

The threshold of hearing can not only differ amongst people , but also due to pathological reasons differ among your left and your right ear. To determine this difference it is possible for example to use the Fowler Test, which is a audiometric procedure, using signal for both ears and compares the test results.

Pathologically the absolute threshold of hearing can be influenced by being exposed to loud noise over a long time (as an industrial construction worker e.g.) or by listening to very loud music over head speakers etc. The small, outer hair cells in the human ear are able to transfer received acoustic signals and to enhance quiet sounds or to lessen loud sounds. If those cells are damaged due to the mentioned factors , the absolute threshold is raised , the capability of enhancement of lower intensity acoustic signals is blocked. On the other hand very loud signals cant be reduced so they appear very uncomfortable and loud. This psychoacoustic phenomenon is called Recruitment effect.

What is the absolute threshold of hearing for humans?

The threshold of hearing is generally reported as the RMS sound pressure of 20 micropascals, i.e. 0 dB SPL, corresponding to a sound intensity of 0.98 pW/m2 at 1 atmosphere and 25 °C. It is approximately the quietest sound a young human with undamaged hearing can detect at 1,000 Hz.

What is meant by the threshold of hearing?

The hearing threshold is the sound level below which a person's ear is unable to detect any sound. For adults, 0 dB is the reference level. A threshold shift is an increase in the hearing threshold for a particular sound frequency.

What is threshold frequency of hearing?

Human hearing is sensitive to sounds from as low as 20 Hz to as high as 20,000 Hz in normal ears.

What is an example of absolute threshold?

Examples of Absolute Threshold Vision - A candle flame 30 miles away. Hearing - A watch ticking 20 feet away. Smell - A drop of perfume in a 6-room house. Taste - A teaspoon of sugar in a gallon of water.