Michael Syskind Pedersen

Speech intelligibility in background noise with ideal binary time-frequency masking

Ideal binary time-frequency masking is a signal separation technique that retains mixture energy in time-frequency units where local signal-to-noise ratio exceeds a certain threshold and rejects mixture energy in other time-frequency units. Two experiments were designed to assess the effects of ideal binary masking on speech intelligibility of both normal-hearing (NH) and hearing-impaired (HI) listeners in different kinds of background interference. The results from Experiment 1 demonstrate that ideal binary masking leads to substantial reductions in speech-reception threshold for both NH and HI listeners, and the reduction is greater in a cafeteria background than in a speech-shaped noise. Furthermore, listeners with hearing loss benefit more than listeners with normal hearing, particularly for cafeteria noise, and ideal masking nearly equalizes the speech intelligibility performances of NH and HI listeners in noisy backgrounds. The results from Experiment 2 suggest that ideal binary masking in the low-frequency range yields larger intelligibility improvements than in the high-frequency range, especially for listeners with hearing loss. The findings from the two experiments have major implications for understanding speech perception in noise, computational auditory scene analysis, speech enhancement, and hearing aid design.

Role of mask pattern in intelligibility of ideal binary-masked noisy speech

Intelligibility of ideal binary masked noisy speech was measured on a group of normal hearing individuals across mixture signal to noise ratio (SNR) levels, masker types, and local criteria for forming the binary mask. The binary mask is computed from time-frequency decompositions of target and masker signals using two different schemes: an ideal binary mask computed by thresholding the local SNR within time-frequency units and a target binary mask computed by comparing the local target energy against the long-term average speech spectrum. By depicting intelligibility scores as a function of the difference between mixture SNR and local SNR threshold, alignment of the performance curves is obtained for a large range of mixture SNR levels. Large intelligibility benefits are obtained for both sparse and dense binary masks. When an ideal mask is dense with many ones, the effect of changing mixture SNR level while fixing the mask is significant, whereas for more sparse masks the effect is small or insignificant.

Effects of noise and working memory capacity on memory processing of speech for hearing-aid users.

Abstract Objectives: It has been shown that noise reduction algorithms can reduce the negative effects of noise on memory processing in persons with normal hearing. The objective of the present study was to investigate whether a similar effect can be obtained for persons with hearing impairment and whether such an effect is dependent on individual differences in working memory capacity. Design: A sentence-final word identification and recall (SWIR) test was conducted in two noise backgrounds with and without noise reduction as well as in quiet. Working memory capacity was measured using a reading span (RS) test. Study sample: Twenty-six experienced hearing-aid users with moderate to moderately severe sensorineural hearing loss. Results: Noise impaired recall performance. Competing speech disrupted memory performance more than speech-shaped noise. For late list items the disruptive effect of the competing speech background was virtually cancelled out by noise reduction for persons with high working memory capacity. Conclusions: Noise reduction can reduce the adverse effect of noise on memory for speech for persons with good working memory capacity. We argue that the mechanism behind this is faster word identification that enhances encoding into working memory.

Speech perception of noise with binary gains

For a given mixture of speech and noise, an ideal binary time-frequency mask is constructed by comparing speech energy and noise energy within local time-frequency units. It is observed that listeners achieve nearly perfect speech recognition from gated noise with binary gains prescribed by the ideal binary mask. Only 16 filter channels and a frame rate of 100 Hz are sufficient for high intelligibility. The results show that, despite a dramatic reduction of speech information, a pattern of binary gains provides an adequate basis for speech perception.

Blow-up analysis for a system of heat equations coupled through a nonlinear boundary condition

Abstract Consider the system of heat equations uit − Δui = 0 (i = 1,…, k, uk+1 ≔ u1) in Ω × (0,T) coupled through nonlinear boundary conditions ∂u i ∂η = u p i i+1 on ∂Ω × [0,T) . The upper and lower bounds of the blow-up rate is derived.

Fe‐Al2O3 nanocomposites prepared by high‐energy ball milling

Nanocomposites of α‐Fe and α‐Al2O3, prepared by high‐energy ball milling, exhibit coercivities which are enhanced by about two orders of magnitude with respect to the bulk value. The degree of enhancement depends on the volume fraction (xv) of Fe, with a maximum for xv≊0.25. The effect is ascribed to the production of single‐domain magnetic grains. Mossbauer spectroscopy reveals the presence of iron oxide phases which could not be seen by x‐ray and electron diffraction measurements.

Functional analysis in applied mathematics and engineering

Topological and Metric Spaces Banach Spaces Bounded Operators Hilbert Spaces Operators in Hilbert Space Spectral Theory Integral Operators Semigroups of Evolution Sobolev Spaces Interpolation Spaces Linear Elliptic Operators Regularity of Hyperbolic Mixed Problems The Hilbert Uniqueness Method Exercises References

Magnetic properties of magnetic liquids with iron-oxide particles — The influence of anisotropy and interactions

Abstract Magnetic liquids containing iron-oxide particles were investigated by magnetization and Mossbauer measurements. The particles were shown to be maghemite with a spontaneous saturation magnetization M s = 320 kA m −1 at 200 K and a normalized high-field susceptibility χ / M o = 5.1 × 10 −6 m kA −1 , practically independent of temperature. M s increases with decreasing temperature according to an effective Bloch law with an exponent larger than 1.5, as expected for fine magnetic particles. The model of magnetic particles with uniaxial anisotropy and the actual size distribution gives a consistent description of independent measurements of the temperature dependence of the hyperfine field and the isothermal magnetization versus field. From this an effective anisotropy constant of about 4.5 × 10 4 J m −3 is estimated for a particle with diameter 7.5 nm. The magnetic relaxation, as observed in zero-field-cooled magnetization and isothermal remanence decay, is influenced by interactions and strongly dependent on the applied magnetic field.

Coupled diffusion systems with localized nonlinear reactions

This paper deals with the blowup rate and profile near the blowup time for the system of diffusion equations uit − Δui = upii+1(x0, t), (i = 1, …, k, uk+1 := u1) in Ω × (0, T) with boundary conditions ui = 0 on ∂Ω × [0, T). We show that the solution has a global blowup. The exact rate of the blowup is obtained, and we also derive the estimate of the boundary layer and on the asymptotic behavior of the solution in the boundary layer.

Superparamagnetic relaxation in α-Fe particles

Abstract The superparamagnetic relaxation time of carbon-supported α-Fe particles with an average size of 3.0 nm has been studied over a large temperature range by the use of Mossbauer spectroscopy combined with AC and DC magnetization measurements. It is found that the relaxation time varies with temperature in accordance with Neels expression, τ = τ 0 exp( KV/kT ) with τ 0 = (1.0 ± 0.5) × 10 −10 s and K = (1.2 ± 0.2) × 10 5 J m −3 .