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The Theory
behind this method is that the heart rate has a certain bandwidth, which bandpass filter can isolate. After this, the signal has a distinct pattern in the time domain. A heart pulse has a characteristic downstroke and then upstroke, so running a match filter with an example of a good pulse will strength this aspect of detection. The key characteristic of a heart pulse is that it is a short duration high amplitude pulse which can be detected by convolving with a small width boxcar. Finally because the signal is supposed to be a periodic heart rate, and thus pulse, once a general idea of the frequency has been established, convolving with a comb filter can help extract beats from noisy signals. This method can be applied recursively, with each pass detecting the heart rate more accurately, and altering parameters accordingly.
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