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Harmonic Noise Filter (HNF)

This technology effectively cancels 50/60Hz power line interference from ECG and other electrophysiological signals. This technology utilizes SoftScientific proprietary, patent pending algorithm for Harmonic Noise Filtering (HNF). Unlike a notch filter, HNF removes not only the main interference frequency but all of its harmonics as well. HNF technology does not distort the waveform shape. It works similar to adaptive filtering by predicting and subtracting the interference from the recorded noisy signal producing a clean signal that exactly reproduces the signal of interest. However, unlike the classic adaptive filtering, HNF technology does not require a reference signal significantly simplifying both the recording hardware and software.

Technical information:

The algorithm operates in real time with no delay

Learning time (time necessary to estimate exact interference frequency and parameters of its harmonics) is less than half a second

Computational complexity is less than for the corresponding adaptive filter

No artifacts or ringing on pacemaker impulses

No reference signal required

Efficient fixed or floating point implementation

Intracardiac ECG Harmonic Noise Filtering

Harmonic noise filtering

This figure shows an example of HNF application to filtering a very strong 50Hz interference with multiple harmonics from an intracardiac ECG signal. The signal was recorded by a catheter contacting and internal heart wall. The upper plot shows the original (green) and cleaned (red) signals. The bottom two plots shows spectrograms of the original and cleaned signals. It is seen that horizontal lines representing the interference harmonics are almost totally removed on the cleaned signal while the spectral content of interest is preserved.

New! You may now download ECG Filtering demo package.
The package contains a simple graphical demo application and a set of example ECG signals.