I have a problem with my DD-20 giga delay.

When I switch to a different preset, and straight away play a note, the delay stops for about a second, then carry on.

What is the problem?
You might have the cable plugged into the wrong side of the output of the pedal. and its the stereo panning delay, it bounces between two amps, so either change the delay, or check your output and see which channel (left or right) you are sending to your amp or the next pedal.