Ariel Corp., 433 River Rd., Highland Park, NJ 08904 and Res. Lab. Electron., MIT, Cambridge, MA 02139
Jont B. Allen
Gary W. Elko
AT&T Bell Labs., Murray Hill, NJ 07974
Patricia S. Jeng
CUNY, New York, NY 10036
To make measurements a person sometimes has the need for many different test instruments on ones bench. The philosophy behind SYSid (SYStem identification) is to integrate many commonly used test instruments into a single yet accurate and easy to use system. The SYSid software package runs on a DOS platform with the Ariel DSP-16+installed. The theory of operation in SYSid is simple. SYSid excites the system being measured with a stimulus and synchronously averages the measured response of the system. The stimulus can be a chirp, single tone, or multiple tones, MLS, or it can be user-defined (i.e., speech, pink noise, octave-band noise, etc.). It is important to synchronously average a system response in order to obtain accurate phase information. Synchronous averaging also allows one to measure a signal that is below the system noise floor. SYSid then uses FFT techniques to deconvolve the stimulus from the measured response and to further analyze the data. From this basic mode of operation SYSid can perform many types of analyses including phase responses, group delay, impulse response, Hilbert envelope, reverse energy time curve, RT60, waterfall displays, electrical impedance, etc. In addition to these linear measurements, SYSid also provides the capabilities to make distortion measurements due to nonlinearities in the system. These include harmonic distortion, intermodulation distortion, THD+N, input--output functions, and spectral contamination.