DSP Stability

Introduction Notch filters are commonly used to remove narrowband interference from signals. Typical applications include removing mains hum, switching noise, or mechanical vibration tones. In theory, designing a notch filter is straightforward. Once the interference frequency is known, a filter can be placed precisely at that frequency. However, in real engineering systems notch filters often perform poorly. The filter may fail to remove the interference, distort nearby signals, or even introduce numerical instability. ...

Introduction FIR and IIR filters both appear stable in textbook theory. In embedded DSP systems, their real-world behavior can be dramatically different. Engineers frequently discover that designs which simulate perfectly become unstable, noisy, or fragile once deployed. This article explains the practical stability differences between FIR and IIR filters under real numerical constraints. Theoretical Stability vs Practical Stability Mathematically: FIR filters are always stable IIR filters are stable if poles remain inside the unit circle Numerically: ...

Introduction IIR notch filters are widely used to suppress narrowband interference due to their efficiency and sharp frequency selectivity. However, engineers frequently encounter instability when pushing notch bandwidths extremely narrow—commonly referred to as high-Q designs. Symptoms include: unexpected oscillations amplification instead of attenuation drifting frequency response sensitivity to coefficient quantization This article explains the physical and numerical reasons behind high-Q notch instability and outlines deterministic design practices that prevent it. ...