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R Plomp

Publications and source records attributed to R Plomp.

At least 19 recordsLinked to original sources
PubMed1996

[Hearing impairment in quietude and noise; 2 different forms of expression of presbyacusis].

Many elderly persons have problems in understanding speech in the presence of voice babble, music, etc. Fitting a hearing aid often does not improve their speech intelligibility. For a better insight, we should distinguish between two different modes of presbyacusis. The first mode expresses itself in attenuation of all incoming sounds, which can be compensated successfully by the hearing-aid's electronic amplification. The second mode has to do with a reduced capacity of the ear to separate simultaneous sounds. As the hearing aid amplifies both the wanted and the unwanted sounds, its effect is in this case nihil. Extensive investigations have indicated the extent to which each of the two modes is actually present in the elderly. The data have confirmed that the amplification of the hearing aid cannot solve the hearing problems of the majority of the elderly. They need primarily a hearing aid that would help to separate simultaneous sounds. At the moment, the most promising solution of this difficult technical challenge is improving the directional sensitivity.

Aged↗
PubMed1995

Evaluation of a wide range of amplitude-frequency responses for the hearing impaired.

The long-term average frequency spectrum of speech was modified to 25 target frequency spectra in order to determine the effect of each of these spectra on speech intelligibility in noise and on sound quality. Speech intelligibility was evaluated using the test as developed by Plomp and Mimpen (1979), whereas sound quality was examined through judgments of loudness, sharpness, clearness, and pleasantness of speech fragments. Subjects had different degrees of sensorineural hearing loss and sloping audiograms, but not all of them were hearing aid users. The 25 frequency spectra were defined such that the entire dynamic range of each listener, from 5 dB above threshold to 5 dB below UCL, was covered. Frequency shaping of the speech was carried out on-line by means of Finite Impulse Response (FIR) filters. The tests on speech reception in noise indicated that the Speech-Reception Thresholds (SRTs) did not differ significantly for the majority of spectra. Spectra with high levels, especially at low frequencies (probably causing significant upward spread of masking), and also those with steep negative slopes resulted in significantly higher SRTs. Sound quality judgments led to conclusions virtually identical to those from the SRT data: frequency spectra with an unacceptably low sound quality were in most of the cases significantly worse on the SRT test as well. Because the SRT did not vary significantly among the majority of frequency spectra, it was concluded that a wide range of spectra between the threshold and UCL levels of listeners with hearing losses is suitable for the presentation of speech energy. This is very useful in everyday listening, where the frequency spectrum of speech may vary considerably.

Adult↗
PubMed1995

Objective analysis versus subjective assessment of vowels pronounced by deaf and normal-hearing children.

Objective whole-spectrum and formant analyses have been performed on all 15 Dutch vowels pronounced in /C1VC2/ words by 24 deaf and 24 normal-hearing children, in order to develop a model of pronunciation quality for evaluating (deaf) speech; the results as obtained for adult males by Bakkum et al. [J. Acoust. Soc. Am. 94, 1989-2004 (1993)] have been verified and extended. Spectral representations of the vowels were created by determining the output levels of a bank of 16 filters (90-7200 Hz), with 1/3-oct bandwidths and logarithmic spacing of their center frequencies. Spectral differences agree well with subjective differences in pronunciation quality obtained from magnitude estimation and identification experiments. Spectral differences not related to pronunciation quality judgments arise as a consequence of physiological interspeaker differences and variation in fundamental frequency, but these differences can be compensated for by speaker-normalization and F0-compensation procedures. Using principal components analysis (PCA), the vowel spectra can be described by a limited number of dimensions, without losing much information; a description in a two-dimensional PCA subspace still agrees well with the subjective judgments and it also agrees with a description by the first two formants. The whole-spectrum approach provides a determinate, readily interpretable model of pronunciation quality for evaluating vowels. As a practical advantage, its computational requirements are modest and, in conjunction with PCA, the vowel dynamics can be visualized, which makes the approach suitable for vowel training and diagnostics.

Child↗
PubMed1994

Effect of temporal envelope smearing on speech reception.

The effect of smearing the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated for normal-hearing listeners. For this purpose, the speech signal was split up into a series of frequency bands (width of 1/4, 1/2, or 1 oct) and the amplitude envelope for each band was low-pass filtered at cutoff frequencies of 0, 1/2, 1, 2, 4, 8, 16, 32, or 64 Hz. Results for 36 subjects show (1) a severe reduction in sentence intelligibility for narrow processing bands at low cutoff frequencies (0-2 Hz); and (2) a marginal contribution of modulation frequencies above 16 Hz to the intelligibility of sentences (provided that lower modulation frequencies are completely present). For cutoff frequencies above 4 Hz, the SRT appears to be independent of the frequency bandwidth upon which envelope filtering takes place. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 0, 2, 4, 8, or 16 Hz in 1/4-oct bands. Results for 24 subjects indicate that consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of confusions between long and short vowels. In case of consonant recognition, stops appear to suffer most, with confusion patterns depending on the position in the syllable (initial, medial, or final).

Acoustic Stimulation↗
PubMed1994

Effect of reducing slow temporal modulations on speech reception.

The effect of reducing low-frequency modulations in the temporal envelope on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification was investigated. For this purpose, speech was split up into a series of frequency bands (1/4, 1/2, or 1 oct wide) and the amplitude envelope for each band was high-pass filtered at cutoff frequencies of 1, 2, 4, 8, 16, 32, 64, or 128 Hz, or infinity (completely flattened). Results for 42 normal-hearing listeners show: (1) A clear reduction in sentence intelligibility with narrow-band processing for cutoff frequencies above 64 Hz; and (2) no reduction of sentence intelligibility when only amplitude variations below 4 Hz are reduced. Based on the modulation transfer function of some conditions, it is concluded that fast multichannel dynamic compression leads to an insignificant change in masked SRT. Combining these results with previous data on low-pass envelope filtering (temporal smearing) [Drullman et al., J. Acoust. Soc. Am. 95, 1053-1064 (1994)] shows that at 8-10 Hz the temporal modulation spectrum is divided into two equally important parts. Vowel and consonant identification with nonsense syllables were studied for cutoff frequencies of 2, 8, 32, 128 Hz, and infinity, processed in 1/4-oct bands. Results for 12 subjects indicate that, just as for low-pass envelope filtering, consonants are more affected than vowels. Errors in vowel identification mainly consist of reduced recognition of diphthongs and of durational confusions. For the consonants there are no clear confusion patterns, but stops appear to suffer least. In most cases, the responses tend to fall into the correct category (stop, fricative, or vowel-like).

Acoustic Stimulation↗
PubMed1994

Comments on "Evaluating a speech-reception threshold model for hearing-impaired listeners" [J. Acoust. Soc. Am. 93, 2879-2885 (1993)].

As everyday practice as well as laboratory experiments have shown abundantly, the hearing aid falls short in eliminating the difficulties of many subjects with sensorineural hearing losses in understanding speech in noise. The attempt by Lee and Humes to demonstrate the opposite with only 11 spondees as speech-material does not alter this situation. As far as their experiment allows any conclusion, it supports the view that the speech-reception threshold of hearing-impaired listeners is characterized by a distortion factor as well as an attenuation factor.

Aged↗
PubMed1994

Noise, amplification, and compression: considerations of three main issues in hearing aid design.

This paper deals with the following three topics: (1) interfering noise (voice babble, single competing speaker) as the main problem of many hearing-impaired listeners, (2) the amplitude-frequency response of the hearing aid, and (3) the benefit of frequency-dependent compression. Research by the author and his coworkers has shown that: (1) persons with impaired hearing typically need 3 to 6 dB higher speech-to-noise ratios than do normal-hearing listeners--a technically very difficult problem to solve; (2) within a relatively ample range, the speech-reception threshold in noise is independent of the amplitude-frequency response; and (3) the small time constants of syllabic compression deteriorate the speech signal. Multichannel amplification (2-4 channels) with automatic gain control for each channel is recommended, optimally adjusted to keep the (variable) speech signal within the impaired ear's limited dynamic range as well as to preserve the intensity differences of successive speech phonemes.

Acoustic Stimulation↗
PubMed1993

Effect of spectral envelope smearing on speech reception. II.

This paper describes two experiments on the effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in a background of interfering sound. Signal processing is performed by smoothing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. In the first experiment the effect of reduced spectral contrast on the SRT for male speech is investigated and compared with previously obtained results for female speech [ter Keurs et al., J. Acoust. Soc. Am. 91, 2872-2880 (1992)]. Spectral energy is smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct. The results show that, despite the differences in spectral pattern between male and female voices, the SRT in noise increases similarly for both voices for smearing bandwidths over 1/3 oct. In terms of the ripple density of the spectral envelope the results indicate that the range of lower spectral modulations, up to a limit of about 1.5 periods/oct, is sufficient for the intelligibility of speech in interfering sounds. In the second experiment the extent of the threshold difference between a speech masker and a noise masker is investigated for spectral smearing bandwidths of 1/2, 1, and 2 oct. The release from masking found for the speech masker relative to the (steady-state) noise masker decreases with spectral envelope smearing.

Acoustic Stimulation↗
PubMed1993

Objective analysis versus subjective assessment of vowels pronounced by native, non-native, and deaf male speakers of Dutch.

An objective analysis has been performed on all 15 Dutch vowels pronounced in /hVt/ words by nine native Dutch, nine non-native, and six deaf males. Spectral representations of the vowel segments were created by determining the mean output levels of a bank of 16 filters (90-7200 Hz), with 1/3-oct bandwidths and logarithmic spacing of their center frequencies. The adequacy of the objective analysis is determined by the extent to which spectral information provides an accurate description of pronunciation quality. Spectral distances between the 24 utterances of each monophthong agree rather well with subjective distances obtained by listeners in an elaborate paired-comparisons experiment. For the various monophthongs, the correlation coefficients are within the range 0.63 to 0.88; averaging across all 12 monophthongs of each speaker results in a coefficient of 0.94. Furthermore, it appeared that the objective spectral analysis is as reliable as a subjective assessment by magnitude estimation by two to three listeners. Using principal components analysis (PCA), the number of dimensions by which the vowel spectra are described can be reduced. For the various monophthongs the range of the correlation coefficients between subjective distances and objective distances in a two-dimensional PCA subspace is 0.30-0.93. The three groups of speakers can still be distinguished in this subspace. In the extreme case of the deaf speakers all vowels are strongly "neutralized," whereas the different vowels of the native speakers are well separated, especially after speaker normalization; results are less clear for the non-natives.

Deafness↗
PubMed1993

Limited resolution of spectral contrast and hearing loss for speech in noise.

This paper examines the relations among the spectral contrast needed for speech intelligibility, hearing loss for speech in noise, and auditory filter bandwidth. Fifteen hearing-impaired listeners with relatively flat, mild-to-moderate sensorineural losses and eight normal-hearing listeners participated in the study. The spectral contrast needed for speech intelligibility was determined by reducing spectral contrast in the speech signal and measuring the reduction in contrast beyond which the speech-reception threshold (SRT) for sentences in noise increases. Reduction of spectral contrast was accomplished by smearing the envelope of the squared short-time fast Fourier transform by a convolution with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Auditory filter bandwidth was determined by estimating auditory filter shapes at center frequencies of 0.8, 1.6, and 3.2 kHz, using a notched-noise masking paradigm. The results show that limited resolution of spectral contrast is only loosely associated with hearing loss for speech in noise. Moreover, the correlations between the SRT for unsmeared speech and the auditory filter bandwidth at various frequencies were weak.

Acoustic Stimulation↗
PubMed1993

The efficacy of a multichannel hearing aid in which the gain is controlled by the minima in the temporal signal envelope.

A multichannel signal-processing hearing aid in which the gain is controlled by the level of the minima in the sound envelope [outlined by Festen et al., 1990] was evaluated with hearing-impaired listeners. This evaluation is an extension to the work reported by van Dijkhuizen et al. (1990). A first experiment focused on the speech-reception threshold (SRT), i.e. the S/N ratio for 50% intelligibility. The greatest benefit in terms of the SRT from frequency-dependent control of the amplification is expected in conditions where the spectrum of noise exceeds strongly that of the speech in a limited frequency region. In these conditions frequency-dependent amplification may reduce upward spread of masking. We investigated the upper limit of this benefit in conditions of intense frequency-limited interfering noise. Speech and noise were both spectrally shaped according to the line bisecting the listener's dynamic range; however, the level of the noise in one octave band (0.25-0.5 or 0.5-1 kHz) was increased by 20 dB. The results show that frequency-selective attenuation of the signal in the octave band with the 20-dB increase of noise is more beneficial than wide-band gain control, and gives a decrease in SRT of up to 4 dB relative to a condition without gain control. In a subsequent experiment we investigated, for several very common interfering sounds, the effect of controlling the gain by the minima in the signal envelope on both the SRT and the perceived noisiness. Results show that the condition with gain control does not affect the SRT for sentences in the presence of everyday interfering sounds having spectra that are roughly comparable to that of the speech signal; however, it substantially reduces the perceived noisiness. In line with our expectations, the effect of the gain control on the signal was very small for a single voice, and it was greatest in case of sounds with a more or less continuous character (e.g. stationary noise, music). For these last sounds it was found that the growth in perceived noisiness with the increase of input level is equivalent to the growth produced by only about one-fifth of the increase in input level (in decibels) in a condition without gain control.

Acoustic Stimulation↗
PubMed1992

Effect of spectral envelope smearing on speech reception. I.

The effect of reduced spectral contrast on the speech-reception threshold (SRT) for sentences in noise and on phoneme identification, was investigated with 16 normal-hearing subjects. Signal processing was performed by smoothing the envelope of the squared short-time fast Fourier transform (FFT) by convolving it with a Gaussian-shaped filter, and overlapping additions to reconstruct a continuous signal. Spectral energy in the frequency region from 100 to 8000 Hz was smeared over bandwidths of 1/8, 1/4, 1/3, 1/2, 1, 2, and 4 oct for the SRT experiment. Vowel and consonant identification was studied for smearing bandwidths of 1/8, 1/2, and 2 oct. Results showed the SRT in noise to increase as the spectral energy was smeared over bandwidths exceeding the ear's critical bandwidth. Vowel identification suffered more from this type of processing than consonant identification. Vowels were primarily confused with the back vowels /c,u/, and consonants were confused where place of articulation is concerned.

Acoustic Stimulation↗
PubMed1992

Effect of multiple speechlike maskers on binaural speech recognition in normal and impaired hearing.

Speech-reception thresholds (SRT) were measured for 17 normal-hearing and 17 hearing-impaired listeners in conditions simulating free-field situations with between one and six interfering talkers. The stimuli, speech and noise with identical long-term average spectra, were recorded with a KEMAR manikin in an anechoic room and presented to the subjects through headphones. The noise was modulated using the envelope fluctuations of the speech. Several conditions were simulated with the speaker always in front of the listener and the maskers either also in front, or positioned in a symmetrical or asymmetrical configuration around the listener. Results show that the hearing impaired have significantly poorer performance than the normal hearing in all conditions. The mean SRT differences between the groups range from 4.2-10 dB. It appears that the modulations in the masker act as an important cue for the normal-hearing listeners, who experience up to 5-dB release from masking, while being hardly beneficial for the hearing impaired listeners. The gain occurring when maskers are moved from the frontal position to positions around the listener varies from 1.5 to 8 dB for the normal hearing, and from 1 to 6.5 dB for the hearing impaired. It depends strongly on the number of maskers and their positions, but less on hearing impairment. The difference between the SRTs for binaural and best-ear listening (the "cocktail party effect") is approximately 3 dB in all conditions for both the normal-hearing and the hearing-impaired listeners.

Adult↗
PubMed1991

The effect of linguistic entropy on speech perception in noise in young and elderly listeners.

The rationale for a method to quantify the information content of linguistic stimuli, i.e., the linguistic entropy, is developed. The method is an adapted version of the letter-guessing procedure originally devised by Shannon [Bell Syst. Tech. J. 30, 50-64 (1951)]. It is applied to sentences included in a widely used test to measure speech-reception thresholds and originally selected to be approximately equally redundant. Results of a first experiment reveal that this method enables one to detect subtle differences between sentences and sentence lists with respect to linguistic entropy. Results of a second experiment show that (1) in young listeners and with the sentences employed, manipulating linguistic entropy can result in an effect on SRT of approximately 4 dB in terms of signal-to-noise ratio; (2) the range of this effect is approximately the same in elderly listeners.

Adult↗
PubMed1991

The effect of frequency-selective attenuation on the speech-reception threshold of sentences in conditions of low-frequency noise.

Within a study on the merits of a multichannel automatic gain control in hearing aids, the effect of frequency-selective amplification on the masked speech-reception threshold (SRT) for sentences is measured in conditions of seriously disturbing low-frequency noise, with the effect of wideband amplification as a reference. Speech and noise are both spectrally shaped according to the bisector line of the listener's dynamic-range of hearing, but with the noise in a single octave band (0.25-0.5 or 0.5-1 kHz) increased by 20 dB relative to this line. The increase of noise level is steady state in the first experiment, and time varying in the second experiment. Results for 12 normal-hearing and 12 hearing-impaired listeners indicate that, in both experiments, frequency-selective compression of the signal in the octave band with the 20-dB increase of noise is more beneficial than wideband compression. For the hearing-impaired group, wideband compression does not give any systematic change in intelligibility. Frequency-selective compression in steady-state conditions may, for both groups of listeners, give a decrease of masked SRT (relative to a condition without compression) of up to 4 dB for a compression factor of 100%. Roughly comparable effects are seen for frequency-selective compression in time-varying conditions. The superiority of frequency-selective over wideband compression is attributed to a more effective reduction of upward spread of masking.

Adult↗
PubMed1990

Auditive and cognitive factors in speech perception by elderly listeners. II: Multivariate analyses.

In part I of this study [van Rooij et al., J. Acoust. Soc. Am. 86, 1294-1309 (1989)], the validity and manageability of a test battery comprising auditive (sensitivity, frequency resolution, and temporal resolution), cognitive (memory performance, processing speed, and intellectual abilities), and speech perception tests (at the phoneme, spondee, and sentence level) were investigated. In the present article, the results of a selection of these tests for 72 elderly subjects (aged 60-93 years) are analyzed by multivariate statistical techniques. The results show that the deterioration of speech perception in the elderly consists of two statistically independent components: (a) a large component mainly representing the progressive high-frequency hearing loss with age that accounts for approximately two-thirds of the systematic variance of the tests of speech perception and (b) a smaller component (accounting for one-third of the systematic variance of the speech perception tests) mainly representing a general performance decrement due to reduced mental efficiency, which is indicated by a general slowing of performance and a reduced memory capacity. Although both components are correlated with age, it was found that the balance between auditive and cognitive contributions to speech perception performance did not change with age.

Adolescent↗
PubMed1990

Effects of fluctuating noise and interfering speech on the speech-reception threshold for impaired and normal hearing.

The speech-reception threshold (SRT) for sentences presented in a fluctuating interfering background sound of 80 dBA SPL is measured for 20 normal-hearing listeners and 20 listeners with sensorineural hearing impairment. The interfering sounds range from steady-state noise, via modulated noise, to a single competing voice. Two voices are used, one male and one female, and the spectrum of the masker is shaped according to these voices. For both voices, the SRT is measured as well in noise spectrally shaped according to the target voice as shaped according to the other voice. The results show that, for normal-hearing listeners, the SRT for sentences in modulated noise is 4-6 dB lower than for steady-state noise; for sentences masked by a competing voice, this difference is 6-8 dB. For listeners with moderate sensorineural hearing loss, elevated thresholds are obtained without an appreciable effect of masker fluctuations. The implications of these results for estimating a hearing handicap in everyday conditions are discussed. By using the articulation index (AI), it is shown that hearing-impaired individuals perform poorer than suggested by the loss of audibility for some parts of the speech signal. Finally, three mechanisms are discussed that contribute to the absence of unmasking by masker fluctuations in hearing-impaired listeners. The low sensation level at which the impaired listeners receive the masker seems a major determinant. The second and third factors are: reduced temporal resolution and a reduction in comodulation masking release, respectively.

Adolescent↗