In addition to the frequency domain filter, there's the high/low pass filter tool, and the band pass/stop filter tool. Given how fast they operate, I assume they are using an IIR filter rather than an FIR filter. However, in the research I've done on IIR filters, to compute the coefficients you need to use a Z transform (which is a very advanced mathematical concept) but nothing in the dialog boxes for these tools mentions any Z transform, so it appears you may have found an alternate way to computer the coefficients in the IIR filter.
Did you manage to break down the Z transform into a simple set of sines and cosines, sort of like with the discreet fourier transform, such that you only need to compute a few sines and cosines in order to get the coefficients of the IIR filter? If this isn't a trade secret, please let me know. Thanks in advance.
How does Goldwave do filtering?
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Re: How does Goldwave do filtering?
GoldWave uses IIR filters. There are many books that give the equations for calculating the coefficients for certain kinds of filters (low pass, high pass, etc.).