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Environmental changes during the last millennium recorded in subfossil Cladocera, diatoms and sediment geochemistry from Lake El Sol (Central Mexico)

Zawisza E., Cuna E., Caballero M, Ruiz-Fernandez A. C., Szeroczyńska K., Woszczyk W., Zawiska I.

Geological Quarterly

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2017

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Vol. 61, No. 1

81--90

EN

High-altitude lakes, which are very sensitive ecosystems and respond rapidly to climatic changes, are one of the best targets for palaeolimnological studies. Here, we present the record of environmental changes over the last millennium that are recorded in the sediments of El Sol, a tropical, high-altitude, volcanic crater lake on the Nevado de Toluca, Central Mexico. Palaeolimnological reconstructions are based on subfossil Cladocera, diatoms, magnetic susceptibility and chemical analysis of the sediments. In general, Cladocera occurring in tropical regions, and especially at high altitude, have been studied very little. Our data indicate that in the sequence studied, the species diversity of subfossil Cladocera is very low. Only four species were recorded, and the assemblage is dominated by littoral species. Two Cladocera taxa, Alona manueli and Ilyocryptus, found at Lake El Sol are endemic. Cladocera, diatoms and the sediment chemistry show changes in Lake El Sol which are mostly related to climate. The most pronounced climatic signal was obtained for the early Little Ice Age (1350–1625 AD). This cold episode was expressed by a reduction in the frequency of zooplankton (individuals/cm2/yr) and diatoms (valves/g of dry sediment) and by changes in the organic carbon content in the sediment. Our results show that human activity was very limited throughout the study period. According to historical data the presence of humans at the lake shore was mostly occasional, usually for ceremonial and ritual purposes, and humans did not have an important influence on the lake ecosystem. Only one period was identified when human activity was important. This period corresponds to the introduction of fish into the lake at the beginning of the 20th century.

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Virtual Acoustics at the Service of Music Performance and Recording

Woszczyk W., Ko D., Leonard B.

Archives of Acoustics

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2012

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Vol. 37, No. 1

109-113

EN

Virtual or active acoustics refers to the generation of a simulated room response by means of elec- troacoustics and digital signal processing. An artificial room response may include sound reflections and reverberation as well as other acoustic features mimicking the actual room. They will cause the listener to have an impression of being immersed in virtual acoustics of another simulated room that coexists with the actual physical room. Using low-latency broadband multi-channel convolution and carefully measured room data, optimized transducers for rendering of sound fields, and an intuitive touch control user in- terface, it is possible to achieve a very high perceived quality of active acoustics, with a straightforward adjustability. The electroacoustically coupled room resulting from such optimization does not merely produce an equivalent of a back-door reverberation chamber, but rather a fully functional complete room superimposed on the physical room, yet with highly selectable and adjustable acoustic response. The utility of such active system for music recording and performance is discussed and supported with examples.

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Active Acoustics in Concert Halls - A New Approach

Woszczyk W.

Archives of Acoustics

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2011

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Vol. 36, No. 2

379-393

EN

Active acoustics offers potential benefits in music halls having acoustical shortcomings and is a relatively inexpensive alternative to physical modifications of the enclosures. One critical benefit of active architecture is the controlled variability of acoustics. Although many improvements have been made over the last 60 years in the quality and usability of active acoustics, some problems still persist and the acceptance of this technology is advancing cautiously. McGill’s Virtual Acoustic Technology (VAT) offers new solutions in the key areas of performance by focusing on the electroacoustic coupling between the existing room acoustics and the simulation acoustics. All control parameters of the active acoustics are implemented in the Space Builder engine by employing multichannel parallel mixing, routing, and processing. The virtual acoustic response is created using low-latency convolution and a three-way temporal segmentation of the measured impulse responses. This method facilitates a sooner release of the virtual room response and its radiation into the surrounding space. Field tests are currently underway at McGill University involving performing musicians and the audience in order to fully assess and quantify the benefits of this new approach in active acoustics.

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Anechoic measurements of particle-velocity probes compared to pressure gradient and pressure microphones

Woszczyk W., Iwaki M., Sugimoto T., Ono K., de Bree H. E.

Archives of Acoustics

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2007

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Vol. 32, No. 3

643--658

EN

The Microflown is an acoustic particle velocity sensor invented at the University of Twente in Holland in 1994 and commercialized in 1997 [1, 9]. The sensor directly measures particle velocity rather than pressure-gradient as do most unidirectional and bidirectional microphones. The sensor has several interesting operational characteristics however few measurements of the Microflown have been published until now making it difficult for a potential user to assess the merits of this transducer in comparison to high quality condenser microphones commonly used in music and speech recording. This paper offers some insight by presenting anechoic measurements of particle velocity probes compared to the measurements of pressuregradient and pressure microphones (of condenser type) made under identical acoustical conditions at varying distances from a point source having a wide frequency range. Detailed frequency response measurements show how the characteristics of these transducer types are dependent on their distance to the source, and highlight the need of transducer calibration with respect to distance. Very few microphone manufacturers publish frequency response data for more than one reference distance to the source although distance is often used to modify the applied response of the microphone. An additional goal for making these measurements is to establish the relationship between particle velocity and pressure gradient values using the same acoustical conditions. The measurements were made in the large anechoic chamber of the NHK Science and Technical Research Laboratories (STRL) in Tokyo during the April-May of 2006.