signal (version 0.5)

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

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

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)))