Frequency response of digital filter
Compute the z-plane frequency response of an ARMA model or rational IIR filter.
freqz(filt, ...) ## Default S3 method: freqz( filt, a = 1, n = 512, whole = ifelse((is.numeric(filt) && is.numeric(a)), FALSE, TRUE), fs = 2 * pi, ... ) ## S3 method for class 'Arma' freqz( filt, n = 512, whole = ifelse((is.numeric(filt$b) && is.numeric(filt$a)), FALSE, TRUE), fs = 2 * pi, ... ) ## S3 method for class 'Ma' freqz( filt, n = 512, whole = ifelse(is.numeric(filt), FALSE, TRUE), fs = 2 * pi, ... ) ## S3 method for class 'Sos' freqz(filt, n = 512, whole = FALSE, fs = 2 * pi, ...) ## S3 method for class 'Zpg' freqz(filt, n = 512, whole = FALSE, fs = 2 * pi, ...) ## S3 method for class 'freqz' print(x, ...) ## S3 method for class 'freqz' summary(object, ...) ## S3 method for class 'summary.freqz' print(x, ...) freqz_plot(w, h, ...)
filt |
for the default case, the moving-average coefficients of an ARMA
model or filter. Generically, |
... |
for methods of |
a |
the autoregressive (recursive) coefficients of an ARMA filter. |
n |
number of points at which to evaluate the frequency response. If
|
whole |
FALSE (the default) to evaluate around the upper half of the unit circle or TRUE to evaluate around the entire unit circle. |
fs |
sampling frequency in Hz. If not specified (default = 2 * pi), the frequencies are in radians. |
x |
object to be printed or plotted. |
object |
object of class |
w |
vector of frequencies |
h |
complex frequency response H(e^{jω}), specified as a vector. |
The frequency response of a digital filter can be interpreted as the transfer function evaluated at z = e^{jω}.
The 'Matlab' and 'Octave' versions of freqz produce magnitude and
phase plots. The freqz version in the 'signal' package produces
separate plots of magnitude in the pass band (max - 3 dB to max) and stop
(total) bands, as well as a phase plot. The current version produces slightly
different plots. The magnitude plots are separate for stop and pass bands,
but the pass band plot has an absolute lower limit of -3 dB instead of max -
3 dB. In addition a summary method was added that prints out the most
important information about the frequency response of the filter.
For freqz, a list of class 'freqz' with items:
complex array of frequency responses at frequencies f.
array of frequencies.
units of (angular) frequency; either rad/s or Hz.
When results of freqz are printed, freqz_plot will be
called to display frequency plots of magnitude and phase. As with lattice
plots, automatic printing does not work inside loops and function calls, so
explicit calls to print or plot are needed there.
John W. Eaton, Paul Kienzle, pkienzle@users.sf.net.
Port to R by Tom Short,
adapted by Geert van Boxtel, gjmvanboxtel@gmail.com
b <- c(1, 0, -1) a <- c(1, 0, 0, 0, 0.25) freqz(b, a) hw <- freqz(b, a) summary(hw)
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