Electrical audio signal processing systems and devices – Sound effects – Reverberators
Patent
1994-11-18
1999-01-19
Harvey, Minsun Oh
Electrical audio signal processing systems and devices
Sound effects
Reverberators
381 61, H03G 300
Patent
active
058622330
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to assisted reverberation systems. An assisted reverberation system is used to improve and control the acoustics of a concert hall or auditorium.
BACKGROUND ART
There are two fundamental types of assisted reverberation systems. The first is the In-Line System, in which the direct sound produced on stage by the performer(s) is picked up by one or more directional microphones, processed by feeding it through delays, filters and reverberators, and broadcast into the auditorium from several loudspeakers which may be at the front of the hall or distributed around the wall and ceiling. In an In-Line system acoustic feedback (via the auditorium) between the loudspeakers and microphones is not required for the system to work (hence the term in-line).
In-line systems minimise feedback between the loudspeakers and microphones by placing the microphones as close as practical to the performers, and by using microphones which have directional responses (eg cardioid, hyper-cardioid and supercardioid).
There are several examples of in-line systems in use today. The ERES (Early Reflected Energy System) product is designed to provide additional early reflections to a source by the use of a digital processor--see J. Jaffe and P Scarborough: "Electronic architecture. Towards a better understanding of theory and practice"93rd convention of the Audio Engine-ring Society, 1992, San Francisco (preprint 3382 (F-5)). The design philosophy of the system is that feedback between the system loudspeakers and microphones is undesirable since it produces colouration and possible instability.
The STAP (System for Improved Acoustic Performance) product is an in-line system which is designed to improve the acoustic performance of an auditorium taking its acoustic character into account, and without using acoustic feedback between the loudspeakers and microphones--see W. C. J. M. Prinsson and M. Holden, "System for improved acoustic performance", Proceedings of the Institute of Acoustics, Vol. 14, Part 2 pp 933-101, 1992. The system uses a number of supercardioid microphones placed close to the stage to detect the direct sound and some of the early reflected sound energy. Some reverberant energy is also detected, but this is smaller in amplitude than the direct sound. The microphone signals are processed and a number of loudspeakers are used to broadcast the processed sound into the room. The system makes no attempt to alter the room volume appreciably, because--as the designers state--this can lead to a difference between the visual and acoustic impression of the room's size. This phenomenon they termed dissociation. The SIAP system also adds some reverberation to the direct sound.
The ACS (Acoustic Control System) product attempts to create a new acoustic environment by detecting the direct wave field produced by the sound sources on-stage by the use of directional microphones, extrapolating the wave fields by signal processing, and rebroadcasting the extrapolated fields into the auditorium via arrays of loudspeakers--see A. J. Berkhout, "A holographic approach to acoustic control", J. Audio Engineering Society, vol. 36, no. 12, pp 977-995, 1988. The system offers enhancement of the reverberation time by convolving the direct sound with a simulated reflection sequence with a minimum of feedback from the loudspeakers.
The electroacoustic system produced by Lexicon uses a small number of cardioid microphones placed as close as possible to the source, a number of loudspeakers, and at least four time-varying reverberators between the microphones and loudspeakers--see U.S. Pat. No. 5,109,419 and D. Griesinger, "Improving room acoustics through time-variant synthetic reverberation", 90th convention of the Audio Engineering Society, 1991 Paris (preprint 3014 (B-2)). The system is thus in-line. Ideally the number of reverberators is equal to the product of the number of microphones and the number of loudspeakers. The use of directional microphones allows the level of the direct sound to be increased relat
REFERENCES:
patent: 5109419 (1992-04-01), Griesinger
patent: 5142586 (1992-08-01), Berkhout
patent: 5297210 (1994-03-01), Julstrom
Parkin, P.H. & Morgan, K., "Assisted Resonance in the Royal Festival Hall, London: 1965-1969," Journal of the Acoustical Society of America, Apr. 28, 1970, pp. 1025-1035.
DeKoning, S.H., "The MCR System--Multiple-Channel Amplification of Reverberation," Philips Tech. Rev. 41. No. 1, 1983/84, pp. 12-25.
Kawakami, F. & Shimizu, Y., "Active Field Control in Auditoria," Applied Accoustics 31 (1990), pp. 47-75.
Jones, M.H. & Fowweather, F., "Reverberation Reinforcement--an Electro-Acoustical System for Increasing the Reverberation Time of an Auditorium," Acoustica, Vo. 27 (1972), pp. 357-363.
Prinssen, Ir. W.C.J. M. & Holden, M., "System for Improved Acoustic Performance (SIAP)," Proc. I.O.A. vol. 14, Part 2 (1992) pp. 93-101.
Griesinger, David, "Improving Room Acoustics Through Time-Variant Synthetic Reverberation," 90th Convention Audio Engineering Society, Feb. 19-22, 1991.
Berkhout, A.J., DeVries, D., & Vogel, P., "Acoustic Control by Wave Field Synthesis," J. Acoust. Soc. Am. 93 (5), May 1993, pp. 2764-2778.
Browning Clifford W.
Harvey Minsun Oh
Industrial Research Limited
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