par(mfrow=c(2,2))
t = c(1:1000)/1000
x = 1.2*t^2 + 2.1*t + .4*sin(200*t) + 1.1*rnorm(1000)
y = 1.2*t^2 + 2.1*t + 0*sin(200*t) + 1.1*rnorm(1000)
plot(t,x,type="l",xlab="time")
plot(t,y,type="l",xlab="time")
mvspec(y, spans=c(3,3), log="no",ylim=c(0,14),main="")
mvspec(x, spans=c(3,3), log="no",ylim=c(0,14),main="")