equipment a standard signal conditioning amplifier unit 30 a das 20 analog to digital converter board 32 and an rti 815 digital to analog converter board 34 the determination of how to position the baffles 16 is made as follows low frequency accelerometers 24 measure ground motion additional low frequency accelerometers 26 measure structure responses placement of accelerometers 24 and 26 is determined by the building site and the mode shapes of the structure the 34 mode shapes 34 of the structure are determined by how the structure moves when exited by a particular vibrational mode in general the accelerometers 26 should not be place at nodes that is at locations where the structure will not move the output of accelerometers 24 and 26 are processed through a signal conditioning amplifier unit 30 the signal conditioning amplifier unit 30 removes unwanted high frequency noise preferably eliminating frequencies above 20 hertz the conditioned signal is then amplified by the signal conditioning amplifier unit 30 the output of the signal conditioning amplifier unit 30 is converted to a digital signal by an analog to digital converter 32 the analog to digital converter 32 is preferably installed in the processing microcomputer 28 at least two alternate methods of analyzing the digital signals output by the analog to digital converter 32 the preferred method is accomplished by frequency analysis of the ground motion and the building response this analysis utilizes either the time varying moving window fourier analysis technique described in the paper by w chen n keltarnowaz and t w spancer 34 an efficient recursive algorithm for time varying fourier transform 34 ieee trans signal processing vol 41 no 7 july 1993 pp 2488 2490 or the.