Characteristics of Real-World Signal to Noise Ratios and Speech Listening Situations of Older Adults With Mild to Moderate Hearing Loss

Abstract

Objectives: The first objective was to determine the relationship between speech level, noise level, and signal to noise ratio (SNR), as well as the distribution of SNR, in real-world situations wherein older adults with hearing loss are listening to speech. The second objective was to develop a set of prototype listening situations (PLSs) that describe the speech level, noise level, SNR, availability of visual cues, and locations of speech and noise sources of typical speech listening situations experienced by these individuals.

Design: Twenty older adults with mild to moderate hearing loss carried digital recorders for 5 to 6 weeks to record sounds for 10 hours per day. They also repeatedly completed in situ surveys on smartphones several times per day to report the characteristics of their current environments, including the locations of the primary talker (if they were listening to speech) and noise source (if it was noisy) and the availability of visual cues. For surveys where speech listening was indicated, the corresponding audio recording was examined. Speech-plus-noise and noise-only segments were extracted, and the SNR was estimated using a power subtraction technique. SNRs and the associated survey data were subjected to cluster analysis to develop PLSs.

Results: The speech level, noise level, and SNR of 894 listening situations were analyzed to address the first objective. Results suggested that as noise levels increased from 40 to 74 dBA, speech levels systematically increased from 60 to 74 dBA, and SNR decreased from 20 to 0 dB. Most SNRs (62.9%) of the collected recordings were between 2 and 14 dB. Very noisy situations that had SNRs below 0 dB comprised 7.5% of the listening situations. To address the second objective, recordings and survey data from 718 observations were analyzed. Cluster analysis suggested that the participants' daily listening situations could be grouped into 12 clusters (i.e., 12 PLSs). The most frequently occurring PLSs were characterized as having the talker in front of the listener with visual cues available, either in quiet or in diffuse noise. The mean speech level of the PLSs that described quiet situations was 62.8 dBA, and the mean SNR of the PLSs that represented noisy environments was 7.4 dB (speech = 67.9 dBA). A subset of observations (n = 280), which was obtained by excluding the data collected from quiet environments, was further used to develop PLSs that represent noisier situations. From this subset, two PLSs were identified. These two PLSs had lower SNRs (mean = 4.2 dB), but the most frequent situations still involved speech from in front of the listener in diffuse noise with visual cues available.

Conclusions: The present study indicated that visual cues and diffuse noise were exceedingly common in real-world speech listening situations, while environments with negative SNRs were relatively rare. The characteristics of speech level, noise level, and SNR, together with the PLS information reported by the present study, can be useful for researchers aiming to design ecologically valid assessment procedures to estimate real-world speech communicative functions for older adults with hearing loss.

Figure 1

Average audiograms for left and right ears of twenty study participants. Error bars = 1 SD.

Figure 2

Frequency response (2A) and the relationship between the measured and actual level (2B) of the digital audio recorder.

Figure 3

3A. Speech level as a function of noise level reported in the current study (circles and thick black solid curve), Smeds et al. (2015), and Pearsons et al. (1977). Chest-level microphones were used in the current study while ear-level microphones were used in Smeds et al., and Pearson et al. Diagonal light gray line represents where the speech level is equal to the noise level. 3B. Signal-to-noise ratio as a function of noise level reported in the current study.

Figure 4

Distribution of signal-to-noise ratios (SNRs) measured using chest-level microphone. Gray bars represent a histogram (refer to the left y-axis). Dashed curve (refer to the left y-axis) represents an asymmetric peak function that fits the histogram data of occurrence frequency and bin center value. Open circles represent the frequency of occurrence of the SNRs that are lower than a given SNR (i.e., the cumulative frequency; refer to the right y-axis).

Figure 5

Boxplots of speech level, noise level (refer to the left y-axis), and signal-to-noise ratio (SNR; refer to the right y-axis) as a function of self-reported listening environment. The boundaries of the boxes represent the 25th and 75th percentile and the line within the boxes marks the median. Error bars indicate the 10th and 90th percentiles.

Figure 6

Boxplot of signal-to-noise ratio as a function of self-reported noisiness. The boundaries of the box represent the 25th and 75th percentile and the line within the box marks the median. Error bars indicate the 10th and 90th percentiles.

Figure 7

Signal-to-noise ratio (SNR) distribution curve of the current study and histograms of SNRs reported by Pearsons et al. (1977) (7A) and Smeds et al. (2015) (7B). The light gray shade and dark gray shade in Figure 7B represent the histograms of the better SNR ear and worse SNR ear, respectively. Chest-level microphones were used in the current study while ear-level microphones were used in Smeds et al., and Pearson et al.