The MAA is smallest (the listener can best identify small changes in azimuth) when the sound sources are in front of the listener (0° azimuth), and is largest (poorer) when the sound sources are to the side of the listener. The minimum audible angle ( MAA) is the smallest change in the location (azimuth) of two sound sources that can be perceived by a listener. The WRS is a percentage correct score (from 0 to 100%) and is useful in differential diagnosis and counseling. The words are presented at a dB level at which the listener can hear clearly, which for most normal-hearing listeners is ~40 dB louder than the listener’s SRT (i.e., 40 dB SL or sensation level). The WRS is a speech discrimination measure in which the patient repeats a list of 50 common, one syllable (monosyllabic) words. Also, it should be clear that the dB HL associated with the SAT is lower than the dB HL associated with the SRT because one is a detection measure, whereas the other is a threshold measure.Īnother common measure used by audiologists is the word recognition score ( WRS). Therefore, the SAT is a detection measure, whereas the SRT is a threshold measure. Sometimes, an SRT cannot be measured and the audiologist is simply interested in measuring the level (dB HL) where the patient is aware that speech is present ( speech awareness threshold, or SAT). In this case, the words are increased and decreased in 5 dB steps until the audiologist finds the softest level in dB HL at which the patient can correctly repeat the word 50% of the time (hence the term speech recognition threshold). For example, during speech audiometry patients are asked to repeat spondee words (e.g., mushroom, baseball) until a speech recognition threshold ( SRT) is established. What Is the Difference between Detection and Discrimination?ĭetection is simply the ability to determine if a sound is present or absent, whereas discrimination is the ability to determine the difference between two stimuli or sounds. New York: Thieme Medical Publishers, Inc.) For example, at 125 Hz: 0 dB HL = 45 dB SPL, and at 1000 Hz: 0 dB HL = 7 dB SPL. 1.1 Average thresholds across frequency in dB SPL, corresponding to 0 dB HL. Note in Table 1.1 that the dB values are the same regardless of whether they were calculated from intensity (power) or pressure however, a 100-fold increase in intensity is equal to a 10-fold increase in pressure.įig. As a result, it is cumbersome to measure the incredibly small amounts of power associated with the enormous range of intensities that the human ear can hear. According to Gulick, Gescheider, and Frisina (1989), “a dangerously intense sound would represent a power of only about 0.0024 watt” ( p. The reference for dB IL is 10 –16 W/cm 2. A less common method to express sound intensity is in acoustic power by using decibels intensity level, or dB IL. What Is the Difference between dB IL and dB SPL?Īs stated in the previous section, a common method to express the magnitude of a sound is in decibels sound pressure level or dB SPL, for which the reference is 0.0002 dynes/cm 2. Because it is easy to measure dB SPL with a condenser or free-field microphone coupled to a sound level meter, sound measurements are often expressed in dB SPL. The reference for dB SPL is 20 micropascals (20 μPa) or 0.0002 dynes/cm 2. 1.1, is equal to 0 dB HL on the audiometer for the corresponding frequency.ĭecibels in sound pressure level, or dB SPL, refers to the magnitude of the displacement of molecules in the air. Each threshold in dB SPL, which is noted in the table at the bottom of Fig. 1.1, the solid black line represents the average auditory threshold in dB SPL at each audiometric frequency. The reference level for dB HL is “10,” which is related to the average threshold in decibels sound pressure level (dB SPL) for the average, normal-hearing listener. Decibels in hearing level, or dB HL, is commonly used in audiology because it refers to the decibel level on the audiometer. The decibel ( dB) is a logarithmic unit of measurement used to express the magnitude of a sound relative to some reference level. What Is the Difference between dB HL and dB SPL?
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