Quadrature mirror filter

In digital signal processing, a quadrature mirror filter is a filter whose magnitude response is the mirror image around ${\displaystyle \pi /2}$ of that of another filter. Together these filters are known as the Quadrature Mirror Filter pair.

A filter ${\displaystyle H_{1}(z)}$ will be quadrature mirror filter of ${\displaystyle H_{0}(z)}$ if ${\displaystyle H_{1}(z)=H_{0}(-z)}$

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