a<-synth(f=11025, d=1, cf=2000, shape="tria", am=c(50,10), fm=c(1000,10,1000))
par(mfrow=c(2,1))
oscillo(a, f=11025, title="input signal")
echo(a,f=11025,amp=c(0.8,0.4,0.2),delay=c(1,2,3),plot=TRUE,colwave="brown", title="new signal with echoes")