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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Zero-phase filtfilt distortion of weighting filter frequency response?","articleBody":"Great library!\r\n\r\nIn `signal.weigh` there is the zero-phase option that uses `scipy.signal.filtfilt`. \r\n\r\nTo inspect the frequency response of the zero-phase (forwards-backwards operation) filter _Hzp_, it is necessary to calculate the frequency response of the forwards filter _H_ (using `scipy.signal.freqz`), and then multiply it by the complex conjugate _H*_. Doing this shows that the forwards-backwards operation (ie applying the filter two times to the signal) distorts the overall frequency response _Hzp_, which in many cases will not give the desired response. In this case, zero-phase operation pushes the filter response outside the relevant IEC acceptance limits.\r\n\r\nTo avoid this distortion it would be necessary to pre-warp the filter frequencies (in a similar way to compensating for bilinear transform distortion), although I'm unaware of any way to determine the appropriate pre-warping analytically for arbitrary filter responses.\r\n","author":{"url":"https://github.com/mlotinga","@type":"Person","name":"mlotinga"},"datePublished":"2020-02-20T11:16:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/240/python-acoustics/issues/240"}