I had been running the following playlist
Silence (one hour)
Survival Instinct
Silence (one hour)
Dragon Reborn ST4
Silence (one hour)
This meant that over a 25 hour period I was listening to Survival Instinct and Dragon Reborn ST4 five times each.
I have now added an extra three hours of silence so, at this point I am listening to each ultrasonic title three times each in a 24 hour period, as long as I am near the speakers when the tracks play.