How to Safely Symmetrize an INADEQUATE:
Process the 1-D spectrum. Perform 1-D peak-picking. Do not include solvents and impurities into the list of peaks.
Process the 2-D spectrum. Add the 1-D spectrum as an external projection. Verify that the frequency scales of both spectra are correct and accurate.
Select, from the main menu, the visualization mode Format > Contours. Adjust the intensity of the plot. Ideally all the peaks should be visible and random noise should be hidden. If this is not possible because the signals are weak, choose a compromise: show all the plausible signals, at the cost of including a little of noise. The lowest contour will be the initial threshold of the filter we are going to apply. Peaks below the threshold will (initially) disappear.
Choose the command Process > Symmetrize > Inadequate. You will see the filtered spectrum and a dialog sheet over it. The dialog contains a switch called “filter”. Use this switch to compare the spectrum before and after the cleaning. It is important to verify what happens with a different threshold: try moving the slider. Peaks the appears only with lower levels of threshold could be noise. Treat them with suspicion. Only a complete analysis of the spectrum can solve these doubts.
Apart from the threshold, the filter requires 3 parameters. They are less critical, yet it's worth verifying if their values are correct for your compound and your spectrum. To see the effect on the plot after changing a value, click twice the “filter” switch.
Splitting: this is the coupling constant. You can take an approximate value from similar known compounds. If the same molecule exhibits a wide range of couplings, set this parameter to the smallest value.
Linewidth: the average linewidth of a peak. If you can't measure it, set this parameter to twice the digital resolution of the directly revealed (single-quantum) axis.
Spread: the complete width, along the double-quantum axis, of the largest cross-peak.
Continue playing with the threshold until you get the best result. Close the dialog.