The entire documentary can be found on YouTube:
Note the continued, dead-wrong-as-usual insistence that people can’t sing in the voice commonly believed to belong to the other gender, as mentioned 3 minutes into Part 4. It’s a direct parallel to the insistence, in the face of massive and overwhelming evidence to the contrary, that men cannot naturally sing alto without recourse to falsetto. Just as classical Voyse Expurtz suffer from selective deafness when listening to Smokey Robinson and Neil Sedaka, their ears also apparently shut off when they hear Aretha Franklin or the Pointer Sisters. Yes, such voices are rare, but so are good operatic sopranos and baritones. Rarity is not the same as nonexistence for pete’s sake.
The choir featured in the doco is also online and carrying out research into female vocal range; a concomitant research into male vocal range would also likely explode the absurd paranoid myth that voices come in pink and blue only.