data(tico)
f <- 22050
xlim <- c(0.5, 0.9)
par(mfrow = c(2,1), las=1)
dfreq(tico, f, at = seq(0.59, 0.85, by = 0.01), type = "o", xlim = xlim, main = "a measure every 10 ms")
dfreq(tico, f, at = seq(0.59, 0.85, len = 100),  pch = 3, col = "#00000075", xlim = xlim, main = "a specific number of measures (100)")