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Biomedical subjects

M W Hoffman

Publications and source records attributed to M W Hoffman.

5 recordsLinked to original sources
PubMed1996

Simulation of multi-microphone hearing aids in multiple interference environments.

In this study, the advantages of Digital Signal Processing (DSP) hardware for hearing aids are investigated in the context of multiple microphone arrays. One key question in multiple microphone DSP system design remains the allocation of processing resources between the number of microphones and the number of adjustable tap weights applied to each microphone. This study addresses the appropriate distribution of these resources for currently implementable adaptive DSP systems. Comparisons are made by computer simulation that includes acoustic headshadow, reverberation effects and non-ideal microphone array hardware in a wide variety of environments. Variations in the number of interfering sources, the amount of reverberation and the microphone array configuration leads to several important conclusions. Performance improvements provided by the processors are reported as the broadband unweighted signal-to-babble ratio of pre-emphasized speech and speech-shaped babble. Results are demonstrated for both fixed and robust adaptive systems.

Computer Simulation↗
PubMed1994

Robust adaptive microphone array processing for hearing aids: realistic speech enhancement.

The problem of combining the outputs of an array of microphones as a single input for a hearing aid is investigated. Emphasis is placed on the conservative prediction of realistically achievable performance gains provided by the array over a single microphone. Performance improvement is measured as a change in the speech reception threshold (SRT) between single microphone and multimicrophone conditions. Consistent with previous work, predictions of this change in SRT using intelligibility averaged gain, [symbol: see text] are shown to be good. Consequently, this measure is used, along with changes in signal-to-noise ratios (SNRs), to evaluate array performance. The results presented include the effects of acoustic headshadow, small room reverberation, microphone placement uncertainty, and desired speaker location uncertainty. It is in this context that realistic predictions of speech enhancement provided by robust adaptive microphone array processors are discussed. Performance improvements are demonstrated relative to the "best" single microphone in the array for three types of spatial filters: Fixed, robust block processed, and robust adaptive. The performance of the robust block processed arrays is shown to be attainable with adaptive implementations. One fundamental criterion employed in robust beamformer design directly limits the amount of cancellation of the desired signal that can occur.

Adult↗
PubMed1971

Coagulation defects in experimental hepatic injury in the dog.

Alteration in activity of blood coagulation factors in dogs with acute hepatic injury caused by oral carbon tetrachloride dosing was studied. Coagulation Factors II, VII and IX were dramatically reduced within 48 hours but recovered to normal in the next five days. Because surgery is rarely performed on dogs with hepatic necrosis, the use of fresh whole blood tranfusion to improve the coagulation defect in hepatic injury was also studied. Transfusion was found to have only a temporary beneficial effect.

Adrenal Cortex Hormones↗
PubMed1971

Blood coagulation valves in normal sheep and in two mutant strains with hyperbilirubinemia.

Blood coagulation values for normal sheep and lambs, using commercially available reagents for human coagulation, are reported. Of the domestic animal species for which coagulation values have been reported, the sheep most closely resembles those of humans. Factor VII deficiency has been found in some patients with Dubin Johnson syndrome. Sheep with the same defect were found to have no coagulation abnormality.

Animals↗