FIR Filter delay for Realtime Signal Processing

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Ghazian Ghaffar Amna 2021-5-6

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https://ww2.mathworks.cn/matlabcentral/answers/822720-fir-filter-delay-for-realtime-signal-processing

评论： Ghazian Ghaffar Amna 2021-5-27

Hello everyone, i am trying to simulate a realtime signal processing through simulink with all of these block in the picture below. Without the filter, it works fine. But as soon as the filter is introduced we can see a big delay with only 501 filterkoef. Why is this happening ? What can i do to fix this delay ? As for the coefficients, i should be using an impuls where i recorded a clap in my room and then transfer it to matlab. but for the sake of testing i used this instead : filterkoef = [ zeros(1,500) 1 ].

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Answer 1

Christopher McCausland 2021-5-26

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https://ww2.mathworks.cn/matlabcentral/answers/822720-fir-filter-delay-for-realtime-signal-processing#answer_709595

Hi Ghazian,

Your question is more about sampling theroy than matlab. Using an FIR filter will intorduce group delay to the signal. i.e. there is a delay from the signal entering the FIR filter to the signal being output. Group Delay can be calculated as:

Where N is the number of filter taps and T is the sampling time. Assuming a sample frequency of T is 20 Hz, the expected phase delay is 12.5 seconds provided the FIR filter is linear which is about what your image shows.

Are you sampling the signal at a sufficently high enough frequency, I would expect 48 khz or so?

Christopher