This function is used to make a plot of several different
segments with one segment per display. Plots can be made on any
parameter which is returned by `tracks`. The two
obligatory arguments are a segment list and the parameter on which a
plot is to be made.

The following instructions can be used to plot the first two
formant frequencies for the first 12 [i:] segments in the database,
with one panel per segment. Here we also label each graph with the
phonetic element preceeding the [i:], these labels are obtained
using the `label` function ( ).

segs.i <- emu.track("demo", "*", "Phonetic=i:") pre.labs <- emu.requery(segs.i, "Phonetic", sequence=-1) segplot(segs.i[1:12,], "fm", labels=pre.labs)

**Figure 11.4. A segment plot of the second formant for 12 [i:] segments,
each plot is labelled with the phonetic element that preceeds the
[i:].**

Multiple formant frequencies can be plotted simultaneously.
Additionally, the arguments `onset` and
`offset` can be used to include an additional
section of the speech signal to the left or right of the
display. The following instructions plot F1 and F2 for the same
vowels, and include 50 ms of the signal at the vowel onset, and 30
ms at the vowel offset:

segplot(segs.i[1:12,], "fm[1:2]", onset=50, offset=30)

The argument `addlines` draws vertical lines
at specified time points. Specifically, if
`addlines` is a vector of time values, then a
vertical line is drawn on plot `j` at the time
given in `addlines[j]`. If
`addlines` is a matrix, then a series of vertical
lines are drawn on plot j, for the times given in
`addlines[j,i]` (`i`=1, 2,
3\ldots). For example, `segplot` can be used to
mark the boundaries corresponding to the steady-state interval of
vowels. First, formant data is extracted for the same segments as
above. Then the `steady` function is used to
calculate which (25%) section of each segment has the
shortest inter-euclidean distance between data points (in an
F1-F2-F3 space in this case since we use the first three columns of
`fvals`):

fvals <- track(segs.i, "fm") svals <- steady(fvals[,1:3])

The boundary times of the steady-state intervals are given by
`svals$stime` (a 2-columned matrix). These
boundary times can be plotted on F1-F3 displays for each segment by
passing this matrix to the addlines argument of
`segplot`, thus:

> segplot(segs.i, "fm[1:3]", addlines=svals$stime)