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Biomedical subjects

H W Strube

Publications and source records attributed to H W Strube.

7 recordsLinked to original sources
PubMed1989

Evoked otoacoustic emissions as cochlear Bragg reflections.

The reflection of cochlear waves is mathematically described for various assumptions about the dependence of the echo-generating mechanism on place and frequency, without requiring knowledge of the physical details of the mechanism. Any 'wave-related' reflections, caused by intrinsic features of the resonance or active-feedback mechanism, cannot explain long group delays in an approximately shift-similar basilar membrane (BM). Only 'BM related' scattering due to inhomogenities is a possible explanation then. Reflection at a fixed point of the BM could cause only narrow-band evoked otoacoustic emissions (EOAEs). Long group delays in a wider frequency band can be obtained by assuming Bragg reflection at an approximately periodic inhomogenity of BM parameters, possibly due to spatial variations of active undamping. This explains the long delays, about inversely proportional to frequency, the decreasing instantaneous frequency, the often found multi-packet or modulated structure of echoes (vanishing at higher SPL), the spectra of simultaneous and delayed EOAEs and their relation to the threshold of hearing. These phenomena do not necessarily require multiple reflection due to middle/inner-ear mismatch.

Auditory Threshold↗
PubMed1989

Measurement of the glottal impedance with a mechanical model.

An approximate but realistic model of the human larynx was constructed to gain better knowledge of the complex glottal impedance and its dependence on glottal width, flow, and frequency. The glottal width was adjustable from 0 to 3 mm, the flow from 0 to 500 cm3/s. The model was fitted into a system of tubes, through which compressed air could be conducted. Supraglottally, a broadband signal was fed into the tube, and, with a two-microphone directional coupler, the complex glottal impedance at a given reference plane was directly determined as a function of frequency. Since the calculated impedance is sensitively dependent on the definition of the position of the reference plane, it is difficult to obtain quantitative statements about the frequency dependence. Nevertheless, in the presence of flow, it is possible to achieve reliable results by analysis of the relative position of the measured curves. On the one hand, the glottal inductance decreases linearly with increasing flow velocity; on the other hand, it diminishes nonlinearly with decreasing frequency. Finally, some difficulties in the definition of glottal impedance are pointed out.

Glottis↗
PubMed1987

Two magnetic methods for articulatory measurements.

We present two magnetic methods for measuring articulatory activities. Unlike previous methods, the magnetic fields are uniform. Three alternating magnetic fields induce voltages in two detectors, a magnetic potentiometer and a flat coil. Thus we are able to measure jaw and tongue movements during speech production. These methods are biologically safe. The miniaturized detectors do not disturb the speech movements. Some preliminary results are presented. These methods can also be applied for other kinds of vectorial distance measurement.

Computers↗
PubMed1986

Flat-spectrum speech.

Flat-spectrum stimuli, consisting of many equal-amplitude harmonics, produce timbre sensations that can depend strongly on the phase angles of the individual harmonics. For fundamental frequencies in the human pitch range, many realizable timbres have vowel-like perceptual qualities. This observation suggests the possibility of constructing intelligible voiced speech signals that have flat-amplitude spectra. This paper describes a successful experiment of creating several different diphthongs by judicious choice of the phase angles of a flat-spectrum waveform. A possible explanation of the observed vowel timbres lies in the dependence of the short-time amplitude spectra on phase changes.

Acoustic Stimulation↗
PubMed1986

The shape of the nonlinearity generating the combination tone 2f1-f2.

If the level behavior of the cubic difference tone is explained by a static nonlinear characteristic, the correspondence between this characteristic and certain components and quantities of the basilar membrane must be clarified. This is attempted here for a nonlinearity compatible with the idea of an active undamping feedback mechanism saturating at high levels. The relation between asymptotic behavior of the nonlinearity and the measured CDT level dependence is established. Agreement with psychoacoustic data requires a very "softly" compressing characteristic; linear or logarithmic asymptotes are ruled out. The psychoacoustically known level dependence is well reproduced for small primary-frequency differences by cancellation experiments with a digitally simulated basilar-membrane model.

Auditory Perception↗
PubMed1979

Acoustic measurements of articulator motions.

Methods for estimating articulatory data from acoustic measurements are reviewed. First, relations between the vocal-tract area function and formant or impedance data are pointed out. Then the possibility of determining a (discretized) area function from the speech signal itself is considered. Finally, we look at the estimation of certain articulatory parameters rather than the area function. By using a regression method, such parameters can even be estimated independently of any vocal-tract model. Results for real-speech data are given.

Humans↗