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Nov 1989

Volume 86, Issue S1, pp. S1-S125

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back to top Session V. Architectural Acoustics III: Acoustics of Teleconferencing Facilities
Invited Papers
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Teleconferencing—The acoustical environment and directional transducers (A)

J. E. West and G. W. Elko

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S55-S55 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The performance of teleconferencing systems are largely a function of the acoustical environment, the type, and the location of loudspeakers and microphones. Acoustical treatment in most conference rooms is limited to carpeted floors and an acoustical ceiling. For the most part, present microphones are designed to work best under close talking conditions and have omnidirectional, or first‐order unidirectional characteristics. Two small experimental conference rooms have been constructed in which the effects of room parameters such as reverberation time, noise level, and discrete echo control can be independently studied. Broadband (8‐kHz) directional microphones and steerable directional arrays, mostly of second order, are being investigated for a variety of acoustical environmental conditions. The easily adjustable conference rooms allow us to investigate these microphone systems with respect to their directional properties, placement, and steering algorithms. Loudspeaker directional characteristics, and advantages of stereo transmission are also under investigation. The experimental conference rooms and new directional microphones will be described and a discussion of trade‐offs between major parameters for speech reception and transmission will be given.
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Microphones and feedback suppression in teleconferencing (A)

Michael Petterson and Steve Julstrom

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S55-S55 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The effect of room acoustics on microphone placement and selection for teleconferencing systems and current approaches to electroacoustic feedback and echo control in teleconferencing systems will be discussed.
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Teleconference room acoustics (A)

R. Kring Herbert

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S55-S55 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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In dedicated teleconference rooms, there is an acoustical conflict between finishes for optimum microphone pick‐up and those for optimum speech intelligibility within the space. This paper looks at the implications of this for teleconference room finishes and geometries as well as other acoustically critical factors such as sound isolation and ambient noise control. Recommendations are given for optimum performance.
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Room acoustic and sound system design for full duplex teleconference facilities using ceiling‐mounted transducers (A)

Wade R. Bray

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S55-S55 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Room acoustics and the effects of differing conditions on performance of a full‐duplex audio teleconference system, which nulls direct‐path coupling, leaving only coupling by reflected energy, were studied. Room impulse responses and signal‐to‐noise ratios at talker locations and at transducer locations were taken for rooms with differing acoustic conditions, as were binaural recordings of the impulse response tests and of sample teleconferences in the same situations, for subjective comparison and simultaneous analysis. Long working distances from talkers to microphones offer the advantage to users of freedom of placement and movement, but at the cost of strict limits on ambient noise loudness and, more particularly, noise structure (annoyance components). Early reflections within the psychoacoustic fusion time limit described by the Haas effect were found beneficial, while reflections beyond that time proved detrimental both to intelligibility and to circuit function. Discrete energetic late reflections are especially undesirable. Optimization for various room configurations was studied, and criteria presented for obtaining subjectively high‐quality teleconferences between rooms and from rooms to handsets.
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Employing the complete acoustical palette in teleconferencing design (A)

Peter D'Antonio

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S56-S56 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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The prevailing architectural acoustics approach in teleconferencing is “Deader is better” or “No acoustics is better than bad acoustics.” In some situations, this is appropriate, but there are alternative approaches to reflection control in teleconferencing facilities which make use of the entire acoustical palette, namely absorption, reflection, and diffusion. Since the application of diffusive surfaces is new to the teleconferencing environment, a review of the development and the spatial, temporal, and spectral properties will be presented. A teleconferencing design for a board room will be proposed that makes use of an integrated suspended ceiling cloud, containing the various elements of the acoustical palette, as well as lighting, and HVAC elements. This design provides diffuse sound across the conference table, which allows a comfortable conversation level, better acoustic coverage and communication among the participants, as well as a more natural transmitted sound to the other end of the converstation. The ceiling cloud also affords a convenient approach for concealing the necessary HVAC ducts, wiring, etc. and also provides accessibility for maintenance.
Contributed Papers
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An acoustic echo canceler implemented with AT&T DSP16A (A)

Sen M. Kuo and Huan Zhao

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S56-S56 (1989); (1 page)

Online Publication Date: 13 Aug 2005

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Acoustic echo control in teleconferencing and hand‐free phone systems is not trivial because of its special characteristics. Many acoustic cancellation algorithms have been published in recent years but they are either of theoretical consideration or are computer simulations with complicated computation burdens, which makes real‐time implementation impossible. In this paper, a two‐band scheme is proposed to realize an acoustic echo canceler with an AT&T WE DSP16A microprocessor. The structure of the algorithm is optimized so it can give an echo return loss enhancement (ERLE) of more than 25 dB. A double talk detector is developed with the subband adaptive algorithm so that it will ensure full duplex communication. Performance of this canceler is evaluated with both computer simulation results and real‐time test results.
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Adaptive acoustic echo cancellation algorithms in teleconferencing systems (A)

Sen M. Kuo and Huan Zhao

J. Acoust. Soc. Am. Volume 86, Issue S1, pp. S56-S56 (1989); (1 page)

Online Publication Date: 13 Aug 2005

Full Text: | Download PDF

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In teleconferencing systems, acoustic echoes consist of acoustic coupling between louder speakers and microphones and the room reverberations. The echoes could be very annoying and even cause howling if the echo level is high enough. Among many ways of canceling acoustic echoes in teleconferencing system, the adaptive digital signal processing approach is very promising since adaptive filtering has the capability to trace the change of the echo path and cancel echoes actively. Adaptive algorithms to cancel acoustic echoes in both the time and frequency domains are presented, and the computer simulation results are compared in a proposed paper. The algorithms included are LMS, NLMS, LLMS, SDLMS, SELMS, SSLMS for FIR adaptive filtering and RLMS, SHARF, and Pole‐Zero for IIR adaptive filtering. Performance of these adaptation algorithms will be discussed. Subband adaptive filtering algorithm, which has a faster convergence rate, will also be presented.
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