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How to apply a FIR filter

Filter initialization (window method)

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// Initialize window function
expression_pointer<fbase> kaiser = to_pointer(window_kaiser(taps.size(), 3.0));

// Initialize taps
univector<float, 7> taps;
fir_bandpass(taps, 0.2, 0.45, kaiser, true);

// Initialize filter and delay line
filter_fir<float> filter(taps);

You can pass your own coefficients to filter_fir constructor or use another method to calculate coefficients for the filter.

Use apply function to apply the filter to audio.

All the internal state (delay line etc) is preserved between calls to apply. Use reset to reset filter internal state.

How to apply a FIR filter to a plain array (inplace)

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float* data[256];
filter.apply(data); // apply inplace, size is determined automatically

... to a plain array

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float* output[256];
float* input[256]; // size must be same
filter.apply(output, inplace); // read from input, apply, write to output, 
                               // size is determined automatically

... using a pointer and size (inplace)

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float* data;
size_t size;
filter.apply(data, size); // apply inplace, size is explicit

... using two pointers and size

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float* output;
float* input;
size_t size;
filter.apply(output, input, size); // read from input, apply, write to output, 
                                   // size is explicit

... to univector (inplace)

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univector<float> data; // or univector<float, 1000>
filter.apply(data); // apply inplace, size is determined automatically

... to univector

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univector<float> output; // or univector<float, 1000>
univector<float> input; // or univector<float, 1000>
filter.apply(output, input); // size is determined automatically

.. to expression

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univector<float, 1000> output;
auto input = counter();
filter.apply(output, input);

convolve_filter is numerically equal to FIR filter but uses DFT internally for better performance.

See also Filter class definition

See also a gallery with results of applying various FIR filters