Research Resources

This section shares benchmarking and related research information from inside Starkey Hearing Technologies, including detailed methodology used in data collection.

Acceptable Noise Level (ANL)

The Acceptable Noise Level (ANL) test is a measure of the amount of background noise that a person is willing to tolerate1. In recent years it has gained interest among researchers and hearing-care professionals because of its ability to predict, with 85% accuracy, who will be successful with hearing aids2. This statistic is not only useful for counseling purposes, but it implies that if one could understand why different people are able to tolerate different amounts of background noise, then one could gain insight into what makes a patient successful (or unsuccessful) with hearing aids. This knowledge could be used to target hearing-aid solutions for an individual to improve her prognosis with hearing aids.

Performing the ANL test is relatively quick and simple. First, running speech is presented to a listener over headphones or via sound field. Often the Arizona Travelogue is used as the speech stimulus (Cosmos, Inc.). This passage consists of continuous discourse by a male talker discussing his travels in Arizona. Using an adaptive procedure, the listener is first instructed to adjust the level of the speech to a level that is "too loud" then "too soft" then "most comfortable to you." Next, background noise is added, usually multi-talker babble, and the listener is instructed to adjust its level, first to a level that is “too loud to understand the speech” then to a level that is “soft enough for the speech to be very clear” and finally to the highest level that she is “willing to put up with” while following the speech. The difference between the listener’s most comfortable listening level (MCL) and her maximum tolerated background noise level (BNL) is her ANL. The test takes about 2-3 minutes to administer.

A lower ANL score reflects a higher tolerance for background noise. According to Nabelek et al.2, there are three different ANL categories — low, mid and high. Individuals who have “low” ANLs (less than 7 dB) are generally successful hearing-aid wearers, whereas individuals who have “high” ANLs (greater than 13 dB) are generally unsuccessful hearing-aid wearers. People with “mid” ANLs (7 to 13 dB) may or may not be successful with hearing aids. Nabelek et al. showed that most hearing-impaired people had ANLs between 0 and 25 dB; the most frequently-occurring ANLs were around 10-11 dB.

ANLs do not appear to be related to an individual’s age1, 2, gender2, 3, hearing sensitivity1, 2 or preference for the existence of background sound4. At present, it is ambiguous whether ANLs are related to an individual’s speech understanding abilities — some researchers5, 6 suggest that ANLs and speech intelligibility are uncorrelated while other researchers7 suggest that people with better speech intelligibility skills also have lower ANLs. Similarly, studies examining aided and unaided ANLs have produced conflicting results, with Nabelek et al.6 showing that ANLs are the same regardless of the test condition and Ahlstrom et al.7 showing that aided ANLs are lower than unaided ANLs.

In addition to these findings, both directional microphones and noise reduction technology have been shown to improve (lower) listeners’ ANLs by about 2.5-4 dB over the aided condition without these features active8-10. These results are exciting because they suggest that hearing-aid features and hearing-aid signal processing allow people to tolerate higher levels of background noise, which may in turn improve listeners’ success rates with hearing aids. Moreover, if we could understand the cues that individuals are using to determine their tolerance of background noise, this information could be used to better counsel patients and to customize hearing solutions for them. Knowledge of this information could also benefit hearing-aid manufacturers, as it would allow them to predict when, where and for whom certain hearing-aid features would provide benefit. Ideally, this would result in a better first fit, less fine-tuning adjustments, and happier, more satisfied, hearing-aid wearers.

References

  1. Nabelek AK, et al. Toleration of background noises: relationship with patterns of hearing aid use by elderly persons. J Speech Hear Res 1991; 34(3): 679-85.
  2. Nabelek AK, et al. Acceptable noise level as a predictor of hearing aid use. J Am Acad Audiol 2006; 17(9): 626-39.
  3. Rogers DS, et al. The influence of listener's gender on the acceptance of background noise. J Am Acad Audiol 2003; 14(7): 372-82; quiz 401.
  4. Freyaldenhoven MC, et al. Acceptable noise level: reliability measures and comparison to preference for background sounds. J Am Acad Audiol 2006; 17(9): 640-8.
  5. Crowley HJ and Nabelek IV Estimation of client-assessed hearing aid performance based upon unaided variables. J Speech Hear Res 1996; 39(1): 19-27.
  6. Nabelek AK, et al. Comparison of speech perception in background noise with acceptance of background noise in aided and unaided conditions. J Speech Lang Hear Res 2004; 47(5): 1001-11.
  7. Ahlstrom JB, et al. Spatial benefit of bilateral hearing AIDS. Ear Hear 2009; 30(2): 203-18.
  8. Freyaldenhoven MC, et al. Acceptable noise level as a measure of directional hearing aid benefit. J Am Acad Audiol 2005; 16(4): 228-36.
  9. Mueller HG, et al. The effects of digital noise reduction on the acceptance of background noise. Trends Amplif 2006; 10(2): 83-93.
  10. Peeters H, et al. Subjective and objective evaluation of noise management algorithms. J Am Acad Audiol 2009; 20(2): 89-98.

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