Development of the Canadian Digit Triplet Test in English and French.

The Canadian Digit Triplet Test was developed in English and French, the official languages of Canada. Four versions were developed on a common software platform using recordings produced by two fluent bilinguals, one male and one female, following procedures recommended by international guidelines. Phase I of test development focused on homogenizing digit recognition across tokens and positions within the triplets for young adults with normal hearing (n = 48). In phase II, normative data were collected for young adults with normal hearing (n = 64). Statistical properties were found to be uniform across test versions and comparable to digit triplet tests in other languages.

An indirect calculation method for estimating occupational sound exposure from communication headsets.

Measurement of noise exposure from communication headsets is challenging due to the need for specialized equipment, methods, and training. Canadian standard Z107.56-13 [(2013). Measurement of Noise Exposure (Canadian Standards Association, Mississauga, Canada)] introduced a calculation procedure to promote a simpler method that stakeholders in hearing loss prevention could readily apply using widely accessible sound level equipment. The original procedure specified a fixed signal-to-noise ratio (SNR) of 15 dB above the protected background noise when estimating the speech listening level through the headset communication channel. The relationship between background noise level, noise type, headset noise reduction (NR), and speech listening level is revisited in this study. In a noise simulation room, 24 participants were asked to adjust the headset volume while listening to speech and executing a visual reaction task. Results indicate that the growth in speech listening levels with noise is not adequately represented by a fixed SNR, and that one-sided listening increases speech levels by about 5-7 dB in quiet and in noise compared to two-sided listening. Moreover, use of an octave-band procedure with derating to estimate headset NR best captured the speech listening level data. A revised calculation procedure based on linear regression modeling is described with parameters adjusted separately for one-sided and two-sided headsets.

Detection and reaction thresholds for reverse alarms in noise with and without passive hearing protection.

OBJECTIVE: To measure masked detection and reaction thresholds for two reverse alarms (tonal and broadband) and compare results to available standards and psychoacoustic criteria for setting alarm levels. DESIGN: Alarm detection and reaction thresholds were adaptively measured in 80-dBA background noises without hearing protection (Experiment 1), and with a passive earmuff-style hearing protection device (HPD) (Experiment 2). STUDY SAMPLE: Twenty-four young adults with normal hearing in each experimental group. RESULTS: Reverse alarms remained audible at levels well-below background noises [thresholds: -11 to -25 dB signal-to-noise ratio (SNR)], with and without the selected HPD. Detection was more influenced by alarm and noise type, while reaction was more susceptible to HPD use. HPD use resulted in lower detection thresholds by up to 2.5 dB compared to unprotected listening but increased reaction thresholds by 5-10 dB depending on the alarm. CONCLUSIONS: Since noise type appears to have a more limited effect on reaction thresholds, adjusting alarms based on a global dBA method appears preferable to methods based on masked detection thresholds. However, while the >0 dB SNR recommended in ISO 9533 seems adequate for unprotected listening, an additional 5-10 dB may be warranted to elicit the same reaction when the selected HPD is used.

Comparison of direct measurement methods for headset noise exposure in the workplace.

The measurement of noise exposure from communication headsets poses a methodological challenge. Although several standards describe methods for general noise measurements in occupational settings, these are not directly applicable to noise assessments under communication headsets. For measurements under occluded ears, specialized methods have been specified by the International Standards Organization (ISO 11904) such as the microphone in a real ear and manikin techniques. Simpler methods have also been proposed in some national standards such as the use of general purpose artificial ears and simulators in conjunction with single number corrections to convert measurements to the equivalent diffuse field. However, little is known about the measurement agreement between these various methods and the acoustic manikin technique. Twelve experts positioned circum-aural, supra-aural and insert communication headsets on four different measurement setups (Type 1, Type 2, Type 3.3 artificial ears, and acoustic manikin). Fit-refit measurements of four audio communication signals were taken under quiet laboratory conditions. Data were transformed into equivalent diffuse-field sound levels using third-octave procedures. Results indicate that the Type 1 artificial ear is not suited for the measurement of sound exposure under communication headsets, while Type 2 and Type 3.3 artificial ears are in good agreement with the acoustic manikin technique. Single number corrections were found to introduce a large measurement uncertainty, making the use of the third-octave transformation preferable.