Lowpass/Highpass bug

Hi,
It seems that neither lowpass nor highpass functions are working.
One issue that i can see is that they return a float64 slice filled with 0s, due to this line:

output := make([]float64, len(fs))
copy(fs, output)
////// Should be copy(output, fs)

Same bug exists in both functions (Lowpass and Highpass).

Another issue is even when the above is fixed and the returned data is imported into Audacity for spectrum analysis, you can see that it looks identical to unfiltered data, eg: no low/high pass filtering is taking affect.

Thank you