SysID is a computer program that was developed c1980 at Bell Labs, for measurement of linear and nonlinear systems. At that time it was ported to the IBM-PC, and was sold by the Ariel Corp., Highland Park, NJ. Today it is a Matlab/Octave script that works with special hardware manufactured by Mimosa Acoustics of Champaign IL. SysID can measure the complex frequency response and impulse response of any linear system, such as loudspeakers, earphones, and rooms. When coupled with Matlab/Octave, it may be used as an audio-band network analyzer providing a pole-zero analysis of measured complex impedance, either electrical or acoustical. By using synchronous analysis, SysID complements spectrum analyzer functions, and in many cases, can extend the function of a two-channel spectrum analyzer, quickly resulting in highly accurate magnitude and phase results, limited only by the bit-accuracy of the codecs. It can more accurately characterize harmonic distortion and inter-modulation distortion, group delay, phase, impedance, and many other important system features, in near real time, along with a pole-zero analysis. In this presentation I will describe the theory behind SysID, and give a demonstration on the hand-held portable system. There is a long history behind such system. For example a number-theory method called MLS is believed by many to be superior, however this is a topic that needs clarification. MLS uses binary sequences, and therefore cannot directly measure TDH+N, or inter-modulation distortion. These issues are easily overcome by using int-32 sequences having powers of 2 sequence lengths. SysID has been used to measure auditoriums, conference rooms, loudspeaker impulse responses, cochlear potentials, ear canal impedance and reflectance, and many other two-port measurements such as a detailed loudspeaker analysis. The system is used in ECE-403 by students to analyze loud speaker characteristics, and was used to characterize and then model hearing aid receivers [1, 2].
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