The DC Blocking Filter

An IIR first order dc blocking filter.

This submission contains an article describing the ins and outs of the dc blocking filter, giving the relationships between the lone filter coefficient and the cut-on frequency. The implementation aspects are also discussed showing how to interpret the effects of an impulse or step response on the data. The filter is capable of cut-on frequencies far less than 0.01% Nyquist. The article is accompanied by a Matlab function.

The Matlab function dcblock.m is given for the calculation of the lone filter coefficient, a. The syntax includes:

a = dcblock(Fc);
a = dcblock(fc,fs);
[Fc,fc] = dcblock(a,fs);

where Fc is the normalized cut-on frequency, fc is the cut-on frequency in Hz, and fs is the sampling frequency also in Hz. If no outputs are declared at function call, a plot of the filter frequency response is given. Examples provided in the article address the overall performance of the filter in terms of signal distortion, its removal and limitations.