paulvangentcom
commented
1 year ago Hi there,
The quote you give: according to related studies, Baseline wander is a low-frequency noise of around 0.5 to 0.6 Hz. To remove it, a high-pass filter of cutoff frequency 0.5 to 0.6 Hz can be used. is about high-pass filters, which are a different thing from notch filters.
High-pass filters can be used to attenuate unwanted low frequency content from the signal (not just the baseline wander). You can view high-pass filters as something that will reduce the amplitude of all frequencies below a given threshold. Say you set it fo 0.5Hz, then the lower relative to 0.5Hz a frequency component is, the more it will be suppressed.
The main difference with a notch filter is that the notch filter will suppress a specific small frequency range, rather than "everything below" a threshold (or "everything above" in case of a low-pass).
This image might clarify a few things intuitively:
And there's some more info where I took the image from: https://www.vectornav.com/resources/inertial-navigation-primer/math-fundamentals/math-filtering
Hi. Although it is not a code-related issue, but I leave a question since it's hard to find related information.
I wonder why a notch filter of cutoff frequency 0.05Hz is used for remove_baseline_wander function in hp.filtering.
The document says it is a function to remove baseline wander from ECG signals, and according to related studies, Baseline wander is a low-frequency noise of around 0.5 to 0.6 Hz. To remove it, a high-pass filter of cutoff frequency 0.5 to 0.6 Hz can be used. But I found that you recommend a notch filter of cutoff frequency 0.05Hz, and it works well with noisy ECG signal. In contrast, cutoff frequency 0.5 or high-pass filter does not work well...
I wonder why this is happening. It would be great if you could answer my question. Thanks in advance!