Talk:Audiogram

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First, "dbSPL" is wrong (more on that below, including authoritative reference excluding that term). Second, audiograms are also used in reference to species, including non-human species, so "for a person" is wrong in two ways. The correct way to report decibels is with the "dB re" formalism, with the reference effective pressure noted in the measurement.

Other sites using the "dB re" formalism: Oceans of Noise (explicit in defining SPL and SIL in terms of "dB re"), SURTASS LFA, NIST listing SPL in terms of "dB re", and Acoustic Impacts on Marine Mammals. But the best thing I've found has to be ASACOS Rules for Preparation of American National Standards in ACOUSTICS, MECHANICAL VIBRATION AND SHOCK, BIOACOUSTICS, and NOISE, which states:

3.16 Unit symbols 3.16.1 When to use unit symbols In the text of the standard, the unit symbol for a quantity shall be used only when the unit is preceded by a numeral. When the unit is not preceded by a numeral, spell out the name of the unit. In text, even when a numerical value is given, it is desirable to spell out the name of the unit. Moreover, the name shall be spelled out when it first appears in the text, and more often if the text is lengthy. Thus, in text write "...a sound pressure level of 73 dB; or "...a sound pressure level of 73 decibels." Do not write "sound pressure level in dB"; the correct form is "sound pressure level in decibels." Do not write "dB levels", "dB readings", or "dB SPL." Levels or readings are not of decibels; they are of sound pressure levels or some other acoustical quantity. Write out the word "decibel" for such applications, and be sure that the word 'decibel' follows, not precedes the description of the relevant acoustical quantity.

The guidelines given for the National Standards clearly excludes the use of "dB SPL". Wesley R. Elsberry 17:13, 9 April 2006 (UTC)

[edit] Article revision

I can contribute the following text, which is modified and expanded from my page on testing the hearing of whales and dolphins. I'd like to get a little feedback before simply replacing the current text. I think the current text is problematic in several ways.

An audiogram is a graphical representation of how sensitive a subject is to acoustic stimuli across a range of frequencies. Frequency is placed on the X axis, usually with a logarithmic scale, and threshold values, usually in decibels, are plotted on the Y axis. For a behavioral audiogram, researchers obtain the needed threshold values by training subjects to respond to test tones with a specific behavior, which allows the tester to determine which tones have been heard and which were not heard (but see detection theory). For most humans, this may be accomplished by asking them to press a button or speak a word when they hear a test tone. From repeated trials, researchers estimate the threshold of hearing at each test frequency. Researchers do the same for a number of frequencies of test tones to find the audiogram of the subject.
For a behavioral audiogram, the subject is trained to make a response to an acoustic stimulus. The acoustic stimuli are given at many different frequencies and amplitudes, and an estimate is made of the threshold of hearing for each frequency. This approach contrasts with audiograms taken using electronics to pick up the faint signals of the brain's response to those stimuli, or neurophysiological audiograms. A common approach to obtain a neurophysiological audiogram is to monitor the auditory brainstem response (ABR).[1] While a neurophysiological audiogram by ABR has the advantage of not being dependent on having trained subjects, it has the disadvantage of requiring even more sophisticated equipment and impeccable technique in order to carry it off. Also, neurophysiological and behavioral audiograms do not usually agree precisely, even when taken on the same subject. A neurophysiological audiogram tends to indicate several decibels better sensitivity across the tested frequencies than does a behavioral audiogram.
A neurophysiological method for human subjects that is not as precise as ABR, but which can be accomplished with less complex equipment, relies upon otoacoustic emission. The healthy human ear not only transduces received sound energy, but also produces evoked otoacoustic emission of sound in response to acoustic stimuli. A small microphone placed in the external ear canal can pick up these small signals and indicate that the ear can react to a particular stimulus, or indicate a hearing deficit if no response occurs to a normally audible test tone. Such a technique is useful for constructing an audiogram of a human subject who cannot complete a behavioral audiogram, as in severe cases of autism.
As anthropogenic noise becomes more widespread, concerns about impacts of noise on animal populations grows. Audiograms for species become important tools for researchers and policy makers to take into account when dealing with anthropogenic noise. Unfortunately, relatively few species of birds or marine mammals have had audiograms constructed for them. For example, there is no audiogram of any type available for any mysticete cetacean.[2]
A problem with audiograms of non-human subjects is that there is often a tendency to use an audiogram obtained from a single subject and treat that as a representative audiogram for an entire species. This famously led to many years of confusion, from 1972 to 1999, as researchers believed that killer whales could not hear frequencies above about 32 kilohertz, based upon an audiogram of one subject. Later, audiograms taken on other killer whales revealed that their hearing was similar to that of other odontocete cetaceans, with ultrasound sensitivity up to about 120 kilohertz, indicating that the original subject had extensive high-frequency hearing loss.Szymanski et al. 1999
Another issue concerns the completeness of testing for an audiogram. For decades, shad were considered to have an ordinary audiogram for fish, with peak sensitivity under 1 kHz and an upper limit of hearing between 1 and 2 kHz. Further testing, however, demonstrated that shad actually could detect ultrasonic sound up to about 180 kHz.[3]

Wesley R. Elsberry 08:07, 12 April 2006 (UTC)