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R Drullman

Publications and source records attributed to R Drullman.

8 recordsLinked to original sources
PubMed2000

Multichannel speech intelligibility and talker recognition using monaural, binaural, and three-dimensional auditory presentation.

In a 3D auditory display, sounds are presented over headphones in a way that they seem to originate from virtual sources in a space around the listener. This paper describes a study on the possible merits of such a display for bandlimited speech with respect to intelligibility and talker recognition against a background of competing voices. Different conditions were investigated: speech material (words/sentences), presentation mode (monaural/binaural/3D), number of competing talkers (1-4), and virtual position of the talkers (in 45 degrees-steps around the front horizontal plane). Average results for 12 listeners show an increase of speech intelligibility for 3D presentation for two or more competing talkers compared to conventional binaural presentation. The ability to recognize a talker is slightly better and the time required for recognition is significantly shorter for 3D presentation in the presence of two or three competing talkers. Although absolute localization of a talker is rather poor, spatial separation appears to have a significant effect on communication. For either speech intelligibility, talker recognition, or localization, no difference is found between the use of an individualized 3D auditory display and a general display.

Acoustic Stimulation↗
PubMed1997

Effect of reducing temporal intensity modulations on sentence intelligibility.

Modulations in the temporal intensity envelope of 24 1/4-octave bands were reduced by proportionally raising the troughs and lowering the peaks relative to the mean intensity in each band. The effect on intelligibility of various degrees of modulation reduction was investigated by measuring the speech-reception threshold (SRT) in noise. For conditions of severe modulation reduction, the number of correctly received sentences in quiet was scored. The effect of this deterministic modulation reduction was compared to the effect of stochastic modulation reduction obtained with addition of noise. Results for 12 normal-hearing subjects show that in the case of deterministic modulation reduction, intelligibility is reduced to 50% when the modulation-transfer factor equals 0.10, whereas in the case of modulation reduction by addition of noise, this intelligibility is reached already at a modulation-transfer factor of 0.27. This confirms that the effect of additive noise on intelligibility cannot be understood completely as a result of only modulation reduction. As suggested by Drullman [J. Acoust. Soc. Am. 97, 585-592 (1995)] two other factors associated with the addition of noise have to be taken into account: (1) the introduction of nonrelevant modulations, and (2) the corruption of the fine structure.

Adult↗
PubMed1996

Effect of temporal modulation reduction on spectral contrasts in speech.

In this paper the effect of temporal modulation reduction on spectral contrasts is investigated. First, a spectral modulation transfer function (SMTF) is presented as a method to measure the transfer of spectral ripples (sinusoidal periods/oct) in the short-time spectral envelope by comparing the spectral modulation depth of original and processed speech fragments. Measuring the SMTF for speech subjected to uniform reduction of the temporal modulation depth (i.e., modulation-frequency-independent reduction) in 24 1/4-oct bands showed an almost equal uniform reduction of the spectral modulations. Furthermore, the SMTF was used to measure the reduction of spectral contrasts associated with low-pass and high-pass temporal-envelope filtering [Drullman et al., J. Acoust. Soc. Am.95, 1053-1064 and 2670-2680 (1994a, b)]. For a perceptual evaluation, sentences were processed to reduce spectral contrasts and the speech-reception threshold (SRT) in noise was measured with ten normal-hearing subjects. Comparison of the results with those obtained previously after temporal-envelope filtering revealed that the SRT-effect of temporal high-pass filtering can be completely accounted for by the associated reduction of spectral contrasts. However, this relationship cannot be demonstrated conclusively in the case of temporal low-pass filtering.

Adolescent↗
PubMed1995

Temporal envelope and fine structure cues for speech intelligibility.

This paper describes a number of listening experiments to investigate the relative contribution of temporal envelope modulations and fine structure to speech intelligibility. The amplitude envelopes of 24 1/4-oct bands (covering 100-6400 Hz) were processed in several ways (e.g., fast compression) in order to assess the importance of the modulation peaks and troughs. Results for 60 normal-hearing subjects show that reduction of modulations by the addition of noise is more detrimental to sentence intelligibility than the same degree of reduction achieved by direct manipulation of the envelope; in some cases the benefit in speech-reception threshold (SRT) is almost 7 dB. Two crossover levels can be defined in dividing the temporal envelope into two equally important parts. The first crossover level divides the envelope into two perceptually equal parts: Removing modulations either chi dB below or above that level yields the same intelligibility score. The second crossover level divides the envelope into two acoustically equal peak and trough parts. The perceptual level is 9-12 dB higher than the acoustic level, indicating that envelope peaks are perceptually more important than troughs. Further results showed that 24 intact temporal speech envelopes with noise fine structure retain perfect intelligibility. In general, for the present type of signal manipulations, no one-to-one relation between the modulation-transfer function and the intelligibility scores could be established.

Adolescent↗
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↗
PubMedDate not supplied

Audio-visual perception of compressed speech by profoundly hearing-impaired subjects.

For many people with profound hearing loss conventional hearing aids give only little support in speechreading. This study aims at optimizing the presentation of speech signals in the severely reduced dynamic range of the profoundly hearing impaired by means of multichannel compression and multichannel amplification. The speech signal in each of six 1-octave channels (125-4000 Hz) was compressed instantaneously, using compression ratios of 1, 2, 3, or 5, and a compression threshold of 35 dB below peak level. A total of eight conditions were composed in which the compression ratio varied per channel. Sentences were presented audio-visually to 16 profoundly hearing-impaired subjects and syllable intelligibility was measured. Results show that all auditory signals are valuable supplements to speechreading. No clear overall preference is found for any of the compression conditions, but relatively high compression ratios (> 3-5) have a significantly detrimental effect. Inspection of the individual results reveals that compression may be beneficial for one subject.

Adolescent↗