| CLIP-SPECTRUM | Set data outside range to given value |
| DROP-CHANNELS | Drop channels asymmetrically from ends of spectrum |
| INVERT-SPECTRUM | Turn spectrum around in physical memory (for AV etc) |
| REMOVE-SPIKES | Look for outliers and set to average of neighbours. |
| SET-CHANNELS | Set nominated channels to constant value |
| TRUNCATE-SPECTRUM | Drop channels symmetrically from ends of spectrum |
SET-CHANNELS may be used to set the value of one or more sequential channels to any desired value. REMOVE-SPIKES looks for data values exceeding a user-defined threshold and sets offending channels to the average of those on either side of them. CLIP-SPECTRUM sets all channels with values outside the specified "clip range" to a specified value. This latter may be useful when writing to FITS data files, for example, to prevent loss of precision.
The x-extent of the spectrum may be modified by a number of commands. TRUNCATE-SPECTRUM drops channels symmetrically from both ends of the spectrum, while DROP-CHANNELS truncates asymmetrically. INVERT-SPECTRUM swaps the data array end-for-end in physical storage, to allow multi-scan arithmetic operations (commands like ADD-SPECTRA and AVERAGE operate purely on a channel by channel basis, without checking that each channel represents data at the same velocity, frequency or whatever: it is possible for two spectra to have the same number of channels and to cover the same velocity range, but nevertheless not to have the same velocities in each channel if the frequency increment in one spectrum is the negative of the other).
SET-CHANNELS, REMOVE-SPIKES and CLIP-SPECTRUM can be used to set unwanted data to the bad channel or ``magic'' value. Data points set to this value are ignored in all applications - they are not visible on plots, and are not used in spectral reduction operations. Where they would otherwise prevent operations, such as addition of two spectra, affected channels in the result are also set to the magic value.