I am given $|H(\omega)|$, I wonder if minimum phase stable causal filter is unique and how to calculate it.
Answer
If $H(\omega)=e^{\alpha(\omega)+j\phi(\omega)}$ is a minimum phase frequency response, then the attenuation $\alpha(\omega)$ and the phase $\phi(\omega)$ are related by the following Hilbert transform relationship:
$$\phi(\omega)=-\frac{1}{\pi}\int_{-\infty}^{\infty}\frac{\alpha(\Omega)}{\omega-\Omega}d\Omega$$
So $\phi(\omega)$ is uniquely determined by $\alpha(\omega)$. This is the corresponding wikipedia entry.
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