Impulse Testing and Peak Clipping
Impulse testing is a popular, efficient means to technically assess the performance of a linear signal processing system. Before meaningful impulsive audio test signals can be devised, used, and interpreted with confidence, a complete understanding of certain fundamental definitions and principles is necessary. These important concepts are reviewed. They include the meaning of linearity, unit impulse and step functions and their approximations, ideal low-pass transient response, bandwidth, and rise time. Without appropriate precautions, impulsive test signals can easily overload a practical system-especially an equalized system-and drive it into the extremely nonlinear mode of operation known as peak clipping. The frequency spectrum of the symmetry properties of clipping are also considered. A specific, practical example is given which illustrates that impulsive overload can easily occur when tests are performed using equalized square waves. It is concluded that careful technical consideration must be given to the program material or program channel capabilities and the system under test in order to select a useful impulsive test signal. In particular, it is necessary to take into account both system bandwidth and sine-wave overload characteristics. Also, knowledge of peak level and minimum rise time of signals to be processed is required.
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