Non causal filter

1. What is causal and non causal filters?
2. Why ideal filters are non causal?
3. Are IIR filters non causal?
4. What is non causal system with example?

What is causal and non causal filters?

A filter is said to be causal if its output depends only on present and past inputs. Conversely, non-causal filters depend also on future inputs.

Why ideal filters are non causal?

Since the filter characteristic H(jω) is an even function, it is typically only shown for ω > 0. Figure A11. 1 shows that h(t) exists for t < 0 whereas the input δ(t) occurs only at t = 0; this indicates that such an ideal filter is a noncausal system.

Are IIR filters non causal?

(v) An IIR filter is linear and time-invariant. (vi) It is causal.

What is non causal system with example?

The non-causal systems can generate an output before the input is given, hence they are also known as anticipative systems. The non-causal systems do not exist in real time. Also, these systems are not physically realisable. The image processing systems are the examples of noncausal systems.