"But around 1450, or even before, composers and performers started to use a contratenor bassus, derived not from the discantus but from the tenor, beneath which they sang alternate 3rds and 5ths, beginning and ending with a unison or octave, and with the cadential octave preceded by a 5th; to the resulting tricinium a new kind of contratenor altus might also be added, by singing alternate 3rds and 4ths above the tenor, beginning and ending with a 5th, and with the cadential 5th preceded by a 4th see exx.3 and 4 below."