Writes composite waveforms made up of pre-existing waveforms. Each contributing waveform requires 4 pfields and can overlap with other waveforms.
size -- number of points in the table. Must be a power-of-2 plus 1 (see f statement).
fna, fnb, etc. -- pre-existing table number to be written into the table.
ampa, ampb, etc. -- strength of wavefoms. These are relative strengths, since the composite waveform may be rescaled later. Negative values are permitted and imply a 180 degree phase shift.
starta, startb, etc. -- where to start writing the fn into the table.
finisha, finishb, etc. -- where to stop writing the fn into the table.
GEN18 was called GEN22 in version 4.18. The name was changed due to a conflict with DirectCsound.