cheby30,
When you use the RIFF, during the first measure you have time (1st 4 bars of arranger D) to enter the CHORD/key that you want the Arranger to play in. After this, based on some chords within a table plus some chords you've just played, the SD5 will perform "intelligently" for you, automatically changing chords for you to play along with. You cannot DELETE the RIFF - to not activate the RIFF, do NOT use ARRANGER "D" for any style that has a RIFF (R - displayed on screen below style name).
Thanks,
AJ