Digital signal and image processing
Speedrun
FIR vs IIR filters in 30 seconds
Digital filters in 30 seconds. Go.
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Lesson notes
Key points
- What a filter does: A digital filter changes which frequencies in a signal survive.
- FIR filter: FIR uses only current and past inputs, no feedback.
- FIR is always stable: No feedback means FIR filters can never blow up.
- IIR filter: IIR feeds past outputs back in, using recursion.
- IIR trade-off: IIR needs fewer coefficients but can become unstable.
- Linear phase: Symmetric FIR filters give linear phase, so no waveform distortion.
Takeaway: FIR: no feedback, always stable. IIR: feedback, efficient, risky.
Quick check: Why can an FIR filter never become unstable?
- It uses fewer coefficients
- It has no output feedback
- It works only on images
FIR outputs depend only on inputs, so there is no feedback to grow without bound.
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