Double BilinearPrewarp(Double Freq, Double FS)
Prewarp an analog (s-domain) cutoff so it maps to the requested digital frequency under the bilinear transform.
| # | Name | Description |
|---|---|---|
| 1 | Freq | Desired digital cutoff frequency, in the range 0 < Freq < 1 (normalised so the Nyquist frequency is 1, i.e. sampling frequency 2). At Freq toward 1 the result grows without bound (tan -> inf). |
| 2 | FS | Sampling frequency |
| 3 | default 2. $T = 1/FS$. |
Returns: Double - The prewarped analog radian frequency omega_a.
Remarks:
Returns the analog frequency omega_a whose image, after the bilinear transform with sampling frequency FS, is the digital frequency Freq. This is the inverse of the bilinear frequency warp and is computed as omega_a = 2 FS tan( (pi Freq)/2 ) . Design an analog prototype at omega_a so that, once Bilinear is applied, the cutoff lands exactly at Freq. The sample period is .
References:
[1] Digital signal processing, Vinay K. Ingle and John G. Proakis, Brooks-Cole, 2000