Biomedical subjects

M R Schroeder

Publications and source records attributed to M R Schroeder.

12 recordsLinked to original sources

PubMed1992

Isolation and characterization of pro-barley lectin expressed in Escherichia coli.

Lectins are a class of proteins with specific carbohydrate-binding properties found in a wide variety of plants and animals. Gramineae lectins are presumably defense-related proteins in plants that exert their effect by binding to N-acetylglucosamine. Barley lectin is a vacuolar protein synthesized with an amino-terminal signal sequence for entering the secretory pathway and a carboxyl-terminal propeptide necessary for proper targeting to the vacuole. To analyze the three-dimensional structure of barley lectin with the carboxyl-terminal extension and to investigate whether the conversion of the prolectin into the mature molecule leads to a conformational change, the precursor and the mature forms of barley lectin were expressed in Escherichia coli. Both proteins accumulated in denatured form in inclusion bodies were solubilized in 8 M urea and renatured in a redox buffer system. Active pro- and mature barley lectins were purified to homogeneity by affinity chromatography.

Acetylglucosamine↗

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

Auditory paradox based on fractal waveform.

The synthesis of certain paradoxical acoustic waveforms is described that will sound lower when reproduced at higher speeds (and vice versa). Specifically, one such waveform, when recorded on magnetic tape, will sound a semitone lower (rather than an octave higher) when played back at twice the tape speed. The connection with fractal objects in geometry is illustrated.

Humans↗

PubMed1986

Phase effects in masking related to dispersion in the inner ear.

Phase effects in masking experiments using multitone maskers are usually associated with strong variations in the masker envelope. In this article, psychoacoustic experiments with such maskers that lead to phase-dependent threshold variations of up to 20 dB, although the phase transformation leaves the envelope unchanged, are described. However, after filtering the maskers with a realistic basilar membrane model, the envelopes are different owing to the models phase-dispersive properties. Comparison of model outputs with the experimental results reveals a strong correlation between the two for a wide range of parameters, provided one makes the additional assumption that the ear has a minimum integration time of a few milliseconds.

Auditory Threshold↗

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↗

PubMed1978

Linear prediction analysis of speech based on a pole-zero representation.

Speech analysis and synthesis by linear prediction is based on the assumption that the short-time spectral envelope of speech can be represented by a number of poles. An all-pole representation does not provide an accurate description of speech spectra, particularly for nasals and nasalized sounds. This paper presents a method for characterizing speech in terms of the parameters of a pole-zero model. In this method, an impulse response representing the composite filtering action of the glottal wave, the vocal tract, the radiation, and the speech recording system is first constructed from the speech signal. This impulse response is obtained by performing several stages of all-pole LPC analysis. The pole-zero parameters are determined from the impulse response by solving a set of simultaneous linear equations. The method, being noniterative, is very suitable for automatic analysis of speech. The method has been applied to real speech data and the results show that the speech spectra derived from the pole-zero model agree very closely with the actual spectra derived by direct Fourier analysis.

Acoustics↗

PubMed1975