x<-c(10,12,8,6,5,11,14,9,10,13,7,6,10,14,9,8,12,9,6,9)

fft.mod<-Mod(fft(x)/length(x))
fft.faz<-Arg(fft(x)/length(x))

plot(fft.mod,type="l",lwd=3,col="red", xlab="frekvence",ylab="modul")
plot(fft.faz,type="l",lwd=3,col="blue",xlab="frekvence",ylab="fáze")

Hz<-function(z) {
  1/3*(1+z^-1+z^-2)
}

z<-function(fi) {
  cos(fi)+(0+1i)*sin(fi)
}

fi<-seq(0,2*pi,length.out=1000)

plot(Mod(Hz(z(fi))),type="l",col="red",xaxt="n",lwd=3)
axis(1,at=c(0,500,1000),labels=c("0","π","2π"))

plot(20*log10(Mod(Hz(z(fi))))[1:500],type="l",col="blue",xaxt="n",lwd=3,ylim=c(-80,0))
axis(1,at=c(0,500,1000),labels=c("0","π","2π"))