I have a plot of spectra vs frequency and I am trying to add a specific line through the data and what I have right now is

```
plot(freq, spc, log='xy', type='l')
y.loess <- loess(spc ~ freq, span=0.8, data.frame(x=freq, y=spc))
y.predict <- predict(y.loess, data.frame(x=freq))
lines(freq,y.predict)
lines(freq,y.predict, col='red')

```

This gives me the following 
[![enter image description here](https://i.stack.imgur.com/6K2M1.jpg)](https://i.stack.imgur.com/6K2M1.jpg)

The black part of the graph is correct and what I need but the red line is incorrect what I need should look something like

[![enter image description here](https://i.stack.imgur.com/Z0o0b.jpg)](https://i.stack.imgur.com/Z0o0b.jpg)

I thought loess would work but it's not quite what I am going for. How do I add a line to my data to make it look like the second picture?