ellipord {gsignal}

Elliptic Filter Order

Description

Compute elliptic filter order and cutoff for the desired response characteristics.

Usage

ellipord(Wp, Ws, Rp, Rs, plane = c("z", "s"))

Arguments

Wp, Ws

pass-band and stop-band edges. For a low-pass or high-pass filter, Wp and Ws are scalars. For a band-pass or band-rejection filter, both are vectors of length 2. For a low-pass filter, Wp < Ws. For a high-pass filter, Ws > Wp. For a band-pass (Ws[1] < Wp[1] < Wp[2] < Ws[2]) or band-reject (Wp[1] < Ws[1] < Ws[2] < Wp[2]) filter design, Wp gives the edges of the pass band, and Ws gives the edges of the stop band. For digital filters, frequencies are normalized to [0, 1], corresponding to the range [0, fs/2]. In case of an analog filter, all frequencies are specified in radians per second.

Rp

allowable decibels of ripple in the pass band.

Rs

minimum attenuation in the stop band in dB.

plane

"z" for a digital filter or "s" for an analog filter.

Value

A list of class FilterSpecs with the following list elements:

n

filter order

Wc

cutoff frequency

type

filter type, one of "low", "high", "stop", or "pass".

Rp

dB of passband ripple.

Rs

dB of stopband ripple.

Author(s)

Paulo Neis, [e-mail],
adapted by Charles Praplan.
Conversion to R by Tom Short,
adapted by Geert van Boxtel, [e-mail].

See Also

buttord, cheb1ord, cheb2ord, ellip

Examples

fs <- 10000
spec <- ellipord(1000/(fs/2), 1200/(fs/2), 0.5, 29)
ef <- ellip(spec)
hf <- freqz(ef, fs = fs)
plot(c(0, 1000, 1000, 0, 0), c(0, 0, -0.5, -0.5, 0),
     type = "l", xlab = "Frequency (Hz)", ylab = "Attenuation (dB)",
     col = "red", ylim = c(-35,0), xlim = c(0,2000))
lines(c(5000, 1200, 1200, 5000, 5000), c(-1000, -1000, -29, -29, -1000),
      col = "red")
lines(hf$w, 20*log10(abs(hf$h)))