If the data are SEGY, SEGD, DT1, or Bison/Geometrics data, read from a tape or diskfile, then the programs segyread, segdread, dt1tosu, or bison2su will have set the trace header values so that the output will be ``SU data.''
For data read from some other means, such as an ASCII dataset by a2b, headers have to be added, this is done by using suaddhead. If our dataset consists of a file of binary C-style floats with, say 1024 samples per trace, then the command sequence
% suaddhead < data.bin ns=1024 > data.suwill yield the SU datafile ``data.su.''