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For instance, suppose you need to isolate a 1 millivolt signal riding on a 120 volt power line. The low-pass filter will need a stopband attenuation of at least -120dB. As previously shown, the Blackman window only provides -74dB (one part in five-thousand). Fortunately, greater stopband attenuation is easy to obtain. The input signal can be filtered using a conventional windowed-sinc filter kernel, providing an intermediate signal. The intermediate signal can then be passed through the filter a second time, further increasing the stopband attenuation to -148dB.
Ну и раскатал я губу то. А чем он в таком случае сигнал оцифровывает?
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