signal (version 0.7-6)

cheb1ord: Chebyshev type-I filter order and cutoff

Description

Compute discrete Chebyshev type-I filter order and cutoff for the desired response characteristics.

Usage

cheb1ord(Wp, Ws, Rp, Rs)

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. Frequencies are normalized to [0,1], corresponding to the range [0, Fs/2].

Rp

allowable decibels of ripple in the pass band.

Rs

minimum attenuation in the stop band in dB.

Value

An object of class FilterOfOrder with the following list elements:

n

filter order

Wc

cutoff frequency

Rp

allowable decibels of ripple in the pass band

type

filter type, one of “low”, “high”, “stop”, or “pass”

This object can be passed directly to cheby1 to compute filter coefficients.

References

Octave Forge http://octave.sf.net

See Also

cheby1, FilterOfOrder, buttord

Examples

# NOT RUN {
Fs <- 10000
chord <- cheb1ord(1000/(Fs/2), 1200/(Fs/2), 0.5, 29)
plot(c(0, 1000, 1000, 0, 0), c(0, 0, -0.5, -0.5, 0),
     type = "l", xlab = "Frequency (Hz)", ylab = "Attenuation (dB)")
ch1 <- cheby1(chord)
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(-10,0), xlim = c(0,2000))
hf <- freqz(ch1, Fs = Fs)
lines(hf$f, 20*log10(abs(hf$h)))
# }