Frequency Importance Function Research Articles

Frequency importance functions in simulated bimodal cochlear-implant users with spectral holes.

Frequency importance functions (FIFs) for simulated bimodal hearing were derived using sentence perception scores measured in quiet and noise. Acoustic hearing was simulated using low-pass filtering. Electric hearing was simulated using a six-channel vocoder with three input frequency ranges, resulting in overlap, meet, and gap maps, relative to the acoustic cutoff frequency. Spectral holes present in the speech spectra were created within electric stimulation by setting amplitude(s) of channels to zero. FIFs were significantly different between frequency maps. In quiet, the three FIFs were similar with gradually increasing weights with channels 5 and 6 compared to the first three channels. However, the most and least weighted channels slightly varied depending on the maps. In noise, the patterns of the three FIFs were similar to those in quiet, with steeper increasing weights with channels 5 and 6 compared to the first four channels. Thus, channels 5 and 6 contributed to speech perception the most, while channels 1 and 2 contributed the least, regardless of frequency maps. Results suggest that the contribution of cochlear implant frequency bands for bimodal speech perception depends on the degree of frequency overlap between acoustic and electric stimulation and if noise is absent or present.

Determining Frequency Importance Function for Speech Intelligibility of Persian Monosyllabic Words and the List of Quick Speech in Noise in Persian Language

Background and Aim: The Frequency Importance Function (FIF) is the main component of the Speech Intelligibility Index (SII) for a certain language. The FIF indicates the relative importance of each frequency band as it contributes to speech intelligibility. This study was conducted to determine the FIF for the Persian monosyllabic words and the list of Quick Speech in Noise (QSIN) in Persian language.
 Methods: In this exploration study, 34 monolingual Persian-speaking subjects aged 25–40 years with normal hearing (17 males) were included. The FIF was evaluated for 100 monosyllabic words and 30 sentences of Persian QSIN under 180 different auditory conditions. The speech recognition scores were calculated and crossover frequencies were determined. Then, the relative transfer function was extracted and FIFs were calculated.
 Results: The findings showed that for monosyllabic word material, the FIF had three peaks at 178, 1787, and 4467 Hz and for Persian QSIN, the FIF had an initial peak at about 141 Hz followed by a peak at about 1800 Hz. According to the results, the frequency range 891–8913 Hz is very important for recognition of the Persian words. Moreover, the mean crossover frequencies for the Persian sentences was 1446 Hz.
 Conclusion: For monosyllabic word material in the Persian language, the FIF at 708–1778 Hz is very important for recognition of the Persian monosyllabic words. For sentence material in the Persian Language, the FIF at 708–4467 Hz has the highest importance for recognition of Persian sentences.
 Keywords: Frequency importance function; speech intelligibility index; monosyllabic word; quick speech in noise list; Persian language

Speech Intelligibility Index: A Literature Review

Background and Aim: Speech is known as the most important auditory signal that humans deal with it. Noise can mask speech and prevent spoken information from reaching us. Researchers have been trying to develop indexes to assess speech intelligibility. Speech Intelligibility Index (SII) is one of these indicators and we intend to introduce its nature and applications.
 Recent Findings: SII is a method that numerically demonstrates the ability to hear speech in difficult listening situations. The number 1.0 indicates that all spoken information is available, while 0.0 indicates that the person does not have access to any information. Hearing loss changes a person’s scores on this index, so we need to use corrective factors to more accurately estimate speech intelligibility. In children, the SII score is different from adults. This indicator can be used in the improvement of hearing aid fitting and more accurate adjustment of cochlear implants. The frequency importance function used to calculate SII has a unique shape in each language. Therefore, SII will also differ in different languages, depending on the nature of each language.
 Conclusion: SII has emerged as a practical indicator among objective assessments of speech intelligibility. Many have tried to extend and prepare it for use in different groups. Therefore, care should be taken about the use of this index in hearing-impaired people, children, with hearing aids or cochlear implant patients, etc. Evaluation of this index in other languages can help to better adjust the hearing aid based on the characteristics of each language.
 
 Keywords: Speech intelligibility index; hearing loss; children; hearing aid; cochlear implant; language

Acoustic analysis of the effect of personal protective equipment on speech understanding: lessons for clinical environments

Objective The use of various types of filtering facepiece class 3 (FFP3) mask have become commonplace since the Covid-19 outbreak. These have been evaluated in terms of efficacy regarding aerosol filtration but less emphasis has been placed on the acoustic effects of such masks and their consequences for clinical communication. Design A microphone 65 cm from a sound-producing Head and Torso Simulator (wearing the masks) was used to measure attenuation via a tone sweep. Predicted impact on speech reception in noise was assessed by weighting the attenuations of cochlear excitation patterns by the frequency importance function of the Speech Intelligibility Index. Study sample We evaluated acoustic attenuation properties of seven FFP3 masks and a Type IIR surgical mask (as a comparator). Results The Type IIR mask had the smallest impact on SNR (2.6 dB with visor). Most FFP3s with an addition of a visor (if not already face covering) impacted SNR by approximately 6 dB. The 3 M 6000 was significantly worse (15.8 dB). Conclusions Mouth-and-nose covering FFP3s masks had similar effects on SNR (≈6.2 dB with visor). The Tecmen TM-H2 had several advantages over other masks evaluated. It was reusable, allowed lipreading clues and the attenuation was similar to other FFP3s.

Auditory and auditory-visual frequency-band importance functions for consonant recognition.

The relative importance of individual frequency regions for speech intelligibility has been firmly established for broadband auditory-only (AO) conditions. Yet, speech communication often takes place face-to-face. This study tested the hypothesis that under auditory-visual (AV) conditions, where visual information is redundant with high-frequency auditory cues, lower frequency regions will increase in relative importance compared to AO conditions. Frequency band-importance functions for consonants were measured for eight hearing-impaired and four normal-hearing listeners. Speech was filtered into four 1/3-octave bands each separated by an octave to minimize energetic masking. On each trial, the signal-to-noise ratio (SNR) in each band was selected randomly from a 10-dB range. AO and AV band-importance functions were estimated using three logistic-regression analyses: a primary model relating performance to the four independent SNRs; a control model that also included band-interaction terms; and a different set of four control models, each examining one band at a time. For both listener groups, the relative importance of the low-frequency bands increased under AV conditions, consistent with earlier studies using isolated speech bands. All three analyses showed similar results, indicating the absence of cross-band interactions. These results suggest that accurate prediction of AV speech intelligibility may require different frequency-importance functions than for AO conditions.

Individualized frequency importance functions for listeners with sensorineural hearing loss.

The Speech Intelligibility Index includes a series of frequency importance functions for calculating the estimated intelligibility of speech under various conditions. Until recently, techniques to derive frequency importance required averaging data over a group of listeners, thus hindering the ability to observe individual differences due to factors such as hearing loss. In the current study, the "random combination strategy" [Bosen and Chatterjee (2016). J. Acoust. Soc. Am. 140, 3718-3727] was used to derive frequency importance functions for individual hearing-impaired listeners, and normal-hearing participants for comparison. Functions were measured by filtering sentences to contain only random subsets of frequency bands on each trial, and regressing speech recognition against the presence or absence of bands across trials. Results show that the contribution of each band to speech recognition was inversely proportional to audiometric threshold in that frequency region, likely due to reduced audibility, even though stimuli were shaped to compensate for each individual's hearing loss. The results presented in this paper demonstrate that this method is sensitive to factors that alter the shape of frequency importance functions within individuals with hearing loss, which could be used to characterize the impact of audibility or other factors related to suprathreshold deficits or hearing aid processing strategies.

Open-source speech-processing platforms: An application example

Speedy assessment of frequency-importance functions for a variety of speech materials is possible with an Open-source Speech-Processing (OSP) platform. One such platform is that developed at the University of California San Diego. It provides real-time, six-band, processing of microphone input from ear-level transducer assemblies. This platform was used to provide normative data on a new consonant-contrast test developed for use in studies of hearing-aid self-fitting. Performance of young normally hearing adults was measured under various conditions of low-pass filtering. Because the UCSD system includes two sets of filters whose center and crossover frequencies differ by half an octave, it was possible to test with cut-off frequencies at half-octave intervals from 250 through 8000 Hz. Group mean composite contrast score, after correction for chance, fell to around 50% at a (6 dB) cut-off frequency of 660 Hz. With a cut-off frequency of 1 kHz, group-mean contrast scores were in the region of 30 to 35% for place and clustering, 70% for continuance, and over 90% for voicing. Determining the frequency-importance functions of various speech materials and speech features is just one example of the potential value of OSPs in hearing-science and hearing-aid research.Speedy assessment of frequency-importance functions for a variety of speech materials is possible with an Open-source Speech-Processing (OSP) platform. One such platform is that developed at the University of California San Diego. It provides real-time, six-band, processing of microphone input from ear-level transducer assemblies. This platform was used to provide normative data on a new consonant-contrast test developed for use in studies of hearing-aid self-fitting. Performance of young normally hearing adults was measured under various conditions of low-pass filtering. Because the UCSD system includes two sets of filters whose center and crossover frequencies differ by half an octave, it was possible to test with cut-off frequencies at half-octave intervals from 250 through 8000 Hz. Group mean composite contrast score, after correction for chance, fell to around 50% at a (6 dB) cut-off frequency of 660 Hz. With a cut-off frequency of 1 kHz, group-mean contrast scores were in the region of 30 to 35% for...

Derivation of frequency importance functions for the AzBio sentences.

Although the AzBio test is well validated, has effective standardization data available, and is highly recommended for Cochlear Implant (CI) evaluation, no attempt has been made to derive a Frequency Importance Function (FIF) for its stimuli. This study derived FIFs for the AzBio sentence lists using listeners with normal hearing. Traditional procedures described in studies by Studebaker and Sherbecoe [(1991). J. Speech. Lang. Hear. Res. 34, 427-438] were applied for this purpose. Participants with normal hearing listened to a large number of AzBio sentences that were high- and low-pass filtered under speech-spectrum shaped noise at various signal-to-noise ratios. Frequency weights for the AzBio sentences were greatest in the 1.5 to 2 kHz frequency regions as is the case with other speech materials. A cross-procedure comparison was conducted between the traditional procedure [Studebaker and Sherbecoe (1991). J. Speech. Lang. Hear. Res. 34, 427-438] and the nonlinear optimization procedure [Kates (2013). J. Acoust. Soc. Am. 134, EL459-EL464]. Consecutive data analyses provided speech recognition scores for the AzBio sentences in relation to the Speech Intelligibility Index (SII). The findings of the authors provide empirically derived FIFs for the AzBio test that can be used for future studies. It is anticipated that the accuracy of predicting SIIs for CI patients will be improved when using these derived FIFs for the AzBio test.

Linguistic contributions to frequency importance functions in children with normal hearing

Frequency-importance functions represent the contribution of an individual frequency band to speech recognition and are used to generate weighted estimates of audibility in the Speech Intelligibility Index (SII). To date, nearly all frequency-importance functions have been derived from adult speech perception data. Estimates of audibility based on these functions are increasingly being applied to children who wear hearing aids. Frequency-importance functions based on perceptual data from children and adults do not differ on average (McCreery & Stelmachowicz, 2011), but importance functions derived from children are more variable than those obtained from adults. Numerous factors could influence individual variability in frequency-importance functions for children. The purpose of this study was to examine the influence of language abilities on individual differences in importance functions obtained from children. We hypothesized that children with stronger vocabulary knowledge would have importance-functions that were more adult-like than peers with more limited vocabulary abilities. Frequency-importance functions were derived from a group of 105 children with normal hearing who were between 5-12 years of age and a group of 20 adults with normal hearing. Children with higher vocabulary abilities had frequency-importance functions that were more adult-like than peers with lower vocabulary abilities, after controlling for age.

Frequency importance function for monosyllables in Malayalam

Objectives: The phonetic content of Malayalam is different from English and other Indian languages as it may contain more low frequency energy. The present study aimed to determine the frequency importance function (FIF) for monosyllables of Malayalam Language.Study design: Nineteen monosyllables spoken by a native female Malayalam speaker was used for the study. The speech stimuli were digitally filtered into 20 high pass and 20 low pass conditions. Speech noise was added to create nine conditions with SNRs of +8, +6, +4, +2, 0, −2, −4, −6 and −8 dB. The filtered stimuli were presented at these SNRs to 10 normal-hearing Malayalam speakers and were asked to identify the phonemes.Results: The FIF estimated in Malayalam language was compared with the FIF in English obtained from the published literature. The result shows that Malayalam has more weightage for low frequencies compared to English. The probable reason could be because of the inherent phonetic differences. The use of more nasalized speech which has low frequency content might have led to this result.Conclusions: The results of the study suggest that hearing aid fitting in Malayalam speakers should focus on providing more gain at low frequencies for better hearing aid benefit. The study needs to be performed on a larger population for better generalization of the results.

Frequency importance function of the speech intelligibility index for Mandarin Chinese

The speech intelligibility index (SII) is a widely used objective method of predicting speech intelligibility, in which the frequency importance function (FIF) is a key component. The FIF characterizes the relative contribution of different frequency bands to speech recognition. In this work, FIFs for Mandarin Chinese were derived for monosyllabic words spoken by male and female speakers. These words were phoneme balanced and selected from the word lists of a national standard, which have been used for measuring the articulation index in China since 1995. A pilot experiment was conducted to determine suitable signal-to-noise ratios (SNR) for measuring speech intelligibility. The main experiment was conducted to derive the FIFs using 288 test conditions (4 SNRs×36 filtering conditions×2 speaker genders). The noise was speech-spectrum shaped and it was generated separately for the male and female speech materials. The results show that, using 1/3 octave analysis bands: (1) The FIF averaged across genders has a peak in the frequency range between 1000 and 2500Hz, which is consistent with the FIF for English monosyllabic words; (2) The frequency bands centered at 160, 1600, and 2000Hz are slightly more important for Mandarin Chinese than for English; (3) Male speech is more intelligible than female speech, and the band centered at 160Hz is more important for female than male speech. The FIF differences between Mandarin and English and the effect of speaker gender are analyzed and discussed.

Frequency Importance Functions in Quiet and Noise for Adults With Cochlear Implants.

Several studies have been devoted to understanding the frequency information available to adult users of cochlear implants when listening in quiet. The objective of this study was to construct frequency importance functions for a group of adults with cochlear implants and a group of adults with normal hearing both in quiet and in a +10 dB signal-to-noise ratio. Two groups of adults, 1 with cochlear implants and 1 with normal hearing, were asked to identify nonsense syllables in quiet and in the presence of 6-talker babble while "holes" were systematically created in the speech spectrum. Frequency importance functions were constructed. Results showed that adults with normal hearing placed greater weight on bands 1, 3, and 4 than on bands 2, 5, and 6, whereas adults with cochlear implants placed equal weight on all bands. The frequency importance functions for each group did not differ between listening in quiet and listening in noise. Adults with cochlear implants assign perceptual weight toward different frequency bands, though the weight assignment does not differ between quiet and noisy conditions. Generalizing these results to the broader population of adults with implants is constrained by a small sample size.

Effects of envelope bandwidth on importance functions for cochlear implant simulations.

Frequency-importance functions (FIFs) quantify intelligibility contributions of spectral regions of speech. In previous work, FIFs were considered as instruments for characterizing intelligibility contributions of individual cochlear implant electrode channels. Comparisons of FIFs for natural speech and vocoder-simulated implant processed speech showed that vocoding shifted peak importance regions downward in frequency by 0.5 octaves. These shifts were attributed to voicing cue changes, and may reflect increased reliance on low-frequency information (apart from periodicity cues) for correct voicing perception. The purpose of this study was to determine whether increasing channel envelope bandwidth would reverse these shifts by improving access to voicing and pitch cues. Importance functions were measured for 48 subjects with normal hearing, who listened to vowel-consonant-vowel tokens either as recorded or as output from five different vocoders that simulated implant processing. Envelopes were constructed using filters that either included or excluded pitch information. Results indicate that vocoding-based shifts are only partially counteracted by including pitch information; moreover, a substantial baseline shift is present even for vocoders with high spectral resolution. The results also suggest that vocoded speech intelligibility is most sensitive to a loss of spectral resolution in high-importance regions, a finding with possible implications for cochlear implant electrode mapping.

Improved estimation of frequency importance functions

The Speech Intelligibility Index (SII) estimates speech intelligibility based on the audibility of speech cues across frequency. The frequency importance function gives the relative contribution to the SII of the speech audibility at different frequencies. The frequency importance function is usually estimated from the intelligibility data using a complicated multi-step procedure. This paper presents a new procedure for computing the frequency importance function directly from the intelligibility data based on nonlinear joint optimization of the frequency importance function and the SII curve-fitting parameters. An example of using the new approach is presented for previously published W-22 word list intelligibility data.

Use of a compound approach to derive auditory-filter-wide frequency-importance functions for vowels and consonants

Speech recognition in noise presumably relies on the number and spectral location of available auditory-filter outputs containing a relatively undistorted view of local target signal properties. The purpose of the present study was to estimate the relative weight of each of the 30 auditory-filter wide bands between 80 and 7563 Hz. Because previous approaches were not compatible with this goal, a technique was developed. Similar to the "hole" approach, the weight of a given band was assessed by comparing intelligibility in two conditions differing in only one aspect-the presence or absence of the band of interest. In contrast to the hole approach, however, random gaps were also created in the spectrum. These gaps were introduced to render the auditory system more sensitive to the removal of a single band and their location was randomized to provide a general view of the weight of each band, i.e., irrespective of the location of information elsewhere in the spectrum. Frequency-weighting functions derived using this technique confirmed the main contribution of the 400-2500 Hz frequency region. However, they revealed a complex microstructure, contrasting with the "bell curve" shape typically reported.

The Study of Frequency Importance Function of the Korean Monosyllabic Words

주파수중요기능(Frequency Importance Function, FIF) 은 언어를 인지하기 위한 공헌도를 1/3 또는 1 옥타브 주 파수대역(octave frequency band) 별로 0에서 1까지의 숫자 또는 백분율로 나타낸 것으로 어음명료지수(SpeechIntelligibility Index, SII)의 산출에 있어서 청력역치와 더불어 중요한 요소이다. 초기의 FIF 관련 연구는 다양한 전기음향적인 조건에서 어음 신호가 전화 등의 통신기기를 통하여 어떻게 전달되는지를 예측하기 위한 것으로 미국의 Bell Telephone Laboratories에서 개발하였으며(French & Steinberg, 1947; Fletcher & Galt, 1950), 미국국가 표준기구(American National Standard Institute, ANSI) 는 1969년에 FIF를 미국의 국가표준으로 제정하였다 (ANSI S3.5, 1969). 이후 ANSI는 1997년에 FIF와 관련 된 용어인 \'Articulation index\'를 \'Speech intelligibility index\'라는 용어로 개정하여 현재까지 사용하고 있다 (ANSI S3.5, 1997; ANSI S3.5, 2007). SII의 용도는 난청인의 청력 역치에 따른 어음이해능력을 예측하거나 보청기 착용 전후의 어음인지능력, 즉 보청기의 수행능력평 가(Hou & Thornton, 1994; Pavlovic, 1994; Amlani et al., 2002), 혹은 난청인의 보청기적합에 이용하거나 보청 기적합공식의 산출에도 유용하게 사용할 수 있다(Byrne & Dillon, 1986; Souza et al., 2000; Byrne et al., 2001).

Use of an adaptive-bandwidth protocol to measure importance functions for simulated cochlear implant frequency channels

The Articulation Index and Speech Intelligibility Index predict intelligibility scores from measurements of speech and hearing parameters. One component in the prediction is the frequency-importance function, a weighting function that characterizes contributions of particular spectral regions of speech to speech intelligibility. The purpose of this study was to determine whether such importance functions could similarly characterize contributions of electrode channels in cochlear implant systems. Thirty-eight subjects with normal hearing listened to vowel-consonant-vowel tokens, either as recorded or as output from vocoders that simulated aspects of cochlear implant processing. Importance functions were measured using the method of Whitmal and DeRoy [J. Acoust. Soc. Am. 130, 4032-4043 (2011)], in which signal bandwidths were varied adaptively to produce specified token recognition scores in accordance with the transformed up-down rules of Levitt [J. Acoust. Soc. Am. 49, 467-477 (1971)]. Psychometric functions constructed from recognition scores were subsequently converted into importance functions. Comparisons of the resulting importance functions indicate that vocoder processing causes peak importance regions to shift downward in frequency. This shift is attributed to changes in strategy and capability for detecting voicing in speech, and is consistent with previously measured data.

Audibility-based predictions of speech recognition for children and adults with normal hearing

This study investigated the relationship between audibility and predictions of speech recognition for children and adults with normal hearing. The Speech Intelligibility Index (SII) is used to quantify the audibility of speech signals and can be applied to transfer functions to predict speech recognition scores. Although the SII is used clinically with children, relatively few studies have evaluated SII predictions of children's speech recognition directly. Children have required more audibility than adults to reach maximum levels of speech understanding in previous studies. Furthermore, children may require greater bandwidth than adults for optimal speech understanding, which could influence frequency-importance functions used to calculate the SII. Speech recognition was measured for 116 children and 19 adults with normal hearing. Stimulus bandwidth and background noise level were varied systematically in order to evaluate speech recognition as predicted by the SII and derive frequency-importance functions for children and adults. Results suggested that children required greater audibility to reach the same level of speech understanding as adults. However, differences in performance between adults and children did not vary across frequency bands.

Frequency importance function of Mandarin Chinese speech

The speech intelligibility index (SII) theory objectively assesses speech intelligibility, and the frequency-importance function (FIF), which reflects the relative importance of various frequency bands to speech intelligibility for various languages, occupies the central part of the theory. However, the FIF has not been examined for tonal Chinese Mandarin speech. In this study, considering the characteristics of Mandarin speech, 50 phonemically-balanced one-syllable words were selected as the speech stimuli from the speech corpus "A Method for Calculating Articulation Index (GB/T 15508-1995)", which meets the National Standards of China, and the 1/3 octave FIF was measured and computed with the Fletcher's method. The results show that spectrum regions with frequencies 2000-4000 Hz are more important in Chinese speech than those in English speech. The results predicted by SII model with the new FIF fit the result of human psychophysical studies well, which indicate that the new FIF model is effective and appropriate for assessing the intelligibility of Mandarin speech even when a steady-state noise masker is co-presented. [Supported by the NSFC 60435010; 60535030; 60605016; 30670704]

Development of the Cantonese speech intelligibility index

A Speech Intelligibility Index (SII) for the sentences in the Cantonese version of the Hearing In Noise Test (CHINT) was derived using conventional procedures described previously in studies such as Studebaker and Sherbecoe [J. Speech Hear. Res. 34, 427-438 (1991)]. Two studies were conducted to determine the signal-to-noise ratios and high- and low-pass filtering conditions that should be used and to measure speech intelligibility in these conditions. Normal hearing subjects listened to the sentences presented in speech-spectrum shaped noise. Compared to other English speech assessment materials such as the English Hearing In Noise Test [Nilsson et al., J. Acoust. Soc. Am. 95, 1085-1099 (1994)], the frequency importance function of the CHINT suggests that low-frequency information is more important for Cantonese speech understanding. The difference in ,frequency importance weight in Chinese, compared to English, was attributed to the redundancy of test material, tonal nature of the Cantonese language, or a combination of these factors.