Comparison of digital filters with wavelet multiresolution filter for electrogastrogram

Electrogastrography (EGG) signals have a very low frequency range (0.0083∼0.15 Hz) and extremely low amplitude (10∼100 μV). Consequently, the EGG signal is easily influenced by noises. Both finite impulse response (FIR) and infinite impulse response (IIR) filters need high order filtering or have phase distortions for passing the very narrow bandwidth of the EGG signals. In this study, we decomposed EGG signals using a wavelet multiresolution method using the Daubechies mother wavelet. The EGG signals were decomposed to seven levels. We reconstructed the signal by summing the decomposed signals from level four to seven. To evaluate the performance of the wavelet multiresolution filter (WMF), we used three indices; signal to noise ratio (SNR) and reconstruction squared error (RSE). The WMF performed better in the SNR and RSE than two kinds of FIR and four kinds of IIR filters.