Fig. 4
From: Algorithm to demodulate an electromyogram signal modulated by essential tremor
Effect of high-pass filter (HPF) and low-pass filter (LPF) for two types of noise. In this example, a second-order Butterworth filter with a cutoff frequency of 20 Hz is used as both an HPF and an LPF to process two kinds of noise. In all four graphs, the red dotted line shows the input signal, which is made of two frequency component signals, one being additive and the other multiplicative; the green dashed line shows the output signal of the filters; and the dark blue line shows the ideal output of the filters (in the case of using an LPF, a low-frequency component is ideal output, and in the case of using an HPF, a high-frequency component is ideal output). a Additive noise processed with HPF. b Additive noise processed with LPF. c Multiplicative noise processed with HPF. d Multiplicative noise processed with LPF