A great example of harmonic chain. ADT and possibly varispeed?

Falling from Grace - The Gentle Waves


Why harmonic chain?
The bass increases in steps of 4 notes.


Why artificial double tracking?
It may be heard for example on words ending with "t". Two ts are heard instead of one. "t-t instead of t". This indicates slap back echo. Or 2 vocal lines or waveforms added with a slight time difference.