Brands
Vishay Measurements Group
Interactive Guide
Technical Articles
Digital Signal Processing
|
Digital Signal Processing |
|
Signal Aliasing
Fundamentals When a signal varies with time, we are usually concerned not only with its magnitude but also with how it changes. Oscilloscopes, strip chart recorders and other analog recording devices enable us to make observations of the signal by continuously recording and displaying the measurement data in the time domain. When digital computers are utilized for this purpose, however, the magnitude of the signal is sampled only at fixed intervals of time with a complete loss of continuity between. For data acquired in this form, the mathematics of digital signal processing can be used to analyze the signal in both the time and frequency domains. That is, we can know not only how the magnitude of the signal varied with time, but also what the amplitudes of any oscillations were over a spectrum of frequencies. Care must be taken when dealing with digital data to avoid the creation of false, lower-frequency signals by a phenomenon called aliasing. Do you remember seeing the spoke wheels of a wagon that appeared to turn backwards as the wagon rolled across a television or movie screen? That's a false visual impression caused by aliasing. When the wheel is rotating at a slightly slower rate than that at which the frames are projected, the wheels appear to run in reverse. Further, if the wheels were rotated at the same rate as the frames are projected, the wheel would appear to be static, or not turning at all! ( continued ... ) 
Page 2 of 24 |