"spec".  For multivariate
  time series it plots the marginal spectra of the series or pairs plots
  of the coherency and phase of the cross-spectra.
"plot"(x, add = FALSE, ci = 0.95, log = c("yes", "dB", "no"), xlab = "frequency", ylab = NULL, type = "l", ci.col = "blue", ci.lty = 3, main = NULL, sub = NULL, plot.type = c("marginal", "coherency", "phase"), ...)
plot.spec.phase(x, ci = 0.95, xlab = "frequency", ylab = "phase", ylim = c(-pi, pi), type = "l", main = NULL, ci.col = "blue", ci.lty = 3, ...)
plot.spec.coherency(x, ci = 0.95, xlab = "frequency", ylab = "squared coherency", ylim = c(0, 1), type = "l", main = NULL, ci.col = "blue", ci.lty = 3, ...)"spec".TRUE, add to already existing plot.
    Only valid for plot.type = "marginal".
  ci is strictly
    positive."dB", plot on log10 (decibel) scale (as S-PLUS),
    otherwise use conventional log scale or linear scale.  Logical
    values are also accepted.  The default is "yes" unless
    options(ts.S.compat = TRUE) has been set, when it is
    "dB".  Only valid for plot.type = "marginal".
  plot.type =
      "marginal".  If missing, a description of the smoothing is used.spectrum