To have the frequency values written on top of your peaks you use a tool called “Peak-Picker”. After creating these labels, you can hide or show them with the command “View/Peak Frequencies”. The same command becomes “Delete Frequencies” if you keep the 'Option' key pressed.
The “Peak-Picker” works in combination with a threshold, which may be either visible or implied. The meaning of the threshold is: “a signal has to be as tall as this to be called a peak”. Peaks so tall that they don't fit entirely into the window are also ignored. The threshold is an absolute value and is used to filter both positive and negative peaks. If you want to remove negative peaks, drag the spectrum down so that all negative peaks go out of the window.
You have three ways to fix the threshold, listed here below by priority:
- You create a visible horizontal mark with an alt-click. If you create many marks, the lowest one is the threshold.
- In absence of marks, the point where you click the “Peak-Picker” down automatically defines a threshold.
- When you first select a region, then choose the “Tools/Peak-Picker” command, there is no click. In absence of horizontal marks, the threshold is equal to the parameter “Short Distance”, stored into your personal preferences. The unit for this parameter is the screen point. Into the Preferences dialog you can also specify the color for the displayed frequencies.
If you are not satisfied with the results you get with a certain threshold value, do not delete the frequencies. Simply change the threshold and re-perform the peak-picking. The old frequencies are automatically removed.
To perform a selective peak-picking, select the region of interest with the “Peak-Picker”. To perform a global peak-picking, do a triple-click with the same tool.
If you triple click too near the baseline you will pick too many peaks, while if you triple-click near the window title-bar (not onto it!), you will delete all entries.
To delete selectively some frequencies, set the threshold higher and select them.
If you click into a pick (not over it!), iNMR performs a very selective peak-picking. If one or more frequency labels already exist, the effect is the opposite: the labels are simply deleted.
The frequencies are updated along with the main scale. Normally they use the same font size as other elements, like scales and integrals, unless there are too many frequencies. In this case the font size is reduced to fit the window width.
In 1-D spectroscopy, you can add any entry into the list. With or without the picker tool, Ctrl-click at the desired frequency. From the contextual menu, either select “Pick Mouse”, to enter that frequency, or “Pick Peak” to enter the nearest maximum. The latter command is less selective than normal peak-picking which, instead, whenever two maxima are too near to each other, exclusively picks the highest one.
When the spectrum has 2 dimensions you can use the same peak-picker tool to label the peaks with their frequencies. You can use the tool in three different ways:
- A single click normally creates a label, even if no peak exists, but when you click on existing peaks, they are deleted instead.
- The double click opens a dialog: you can set the parameters and choose the action to perform (creation or deletion of labels).
- A selection performs a selective peak-picking. If the selection already contains a label, the dialog is showed first (the same dialog as in point 2 above).