Delete channels from both ends of the spectrum. May be useful, for example, before adding long AOS spectra to a map file, when only a small velocity range in the middle is of interest, as the savings in memory requirements may be important. Can also be used to eliminate junk channels from the end of an autocorrelation spectrum. The scan header is modified to reflect the change in number of channels and the center frequency.
Examples:
>> drop-channels<CR>
Delete channels from ends of each quadrant
No of points to remove? (low and high) [ 2 5] 1 3<CR>
..
