The velocity of the progression is determined by the given distance of {HEAD ~ the fixtures} at {TAIL ~ a given frequency} 
at
The velocity of the progression is determined by the given distance of { HEAD ~ the fixtures } at { TAIL ~ a given frequency }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL