Typically background noise is of the low frequency variety in most retail and professional settings. The human brain is hardwired to listen to human voice which generates a higher proportion of its critical information content in the range above 1000 CPS. The range of human voice above 1000 CPS has reduced energy while higher energy exists in the range below 1000 CPS. This creates a perception of lower frequencies having a greater impact on the ability to focus on and understand human voice which is most often reported in people with a high frequency hearing change. The human brain is not hardwired to focus on individual pure tones only the combination of tones making up human voice. Asking a person to focus on a pure tone when a human voice or voices are present changes one perception of being able to hear. In fact only in rare cases are there any actual threshold change and this is in the range 500 and below and is usually in the 5 to 10 dB range.
Background noise that subjects being tested complain most often as affecting their tests is generated by human speech or sounds generated by human movement.
The other source is office equipment, heating and air conditioning units which are less often reported as having an impact. It is rare for any levels to exceed 65 for any significant time period especially human voice but its perception of duration is perceived to be much longer.
Background noise in the form of human speech causes distraction when one is attempting to listen to another person talking. Human nature usually means a focus on human voice over individual pure tones. It does not change a person’s actual threshold of hearing only their perceived ability to separate out the background speech sounds from the ones they are trying or want to hear.
Picking out an individual pure tone from background noise can be done with very little difficulty. The possible exception is in the low frequency range where background noise is most prevalent and steady state and that is at or below 500 Hz. (CPS). 500 Hz has it greatest influence if a person has hearing within the normal adult range at 500 Hz that is better than 20dB. The impact could shift this frequency by 10dB. This shift has minimal influence on the person’s test results and would only influence their classification and level in rare circumstance. The actual impact on the polynomials could be dealt with by calibration or modification of the classification system but neither is advisable because of its minor influence on the test. Using data mining of the confidence coefficients is the best tool for determining the influence of background noise on test results for any group of individuals or test location.
The most common reaction to background noise is one of frustration thinking their test results will be made worse by another person or persons talking. This in fact would be rare even at 500 and will not impact higher frequencies except in rare circumstances.
In the worst case the level shift at 500 would generate a classification that produced a false positive finding which would be addressed by a follow up test. False positive findings in a screening program are common while false negative findings are considered more serious in screening programs.
Errol Davis ©
Audiologist 2013
