I think El's title was almost definitely voice of lights. Reasoning:
- That's the only title we see given by a singer a human.
- El is clearly fascinated by godlight, he appears to be the new fused evil mad investiture scientist bad guy.
- El was likely stripped of being able to hear the rhythms of Roshar and not restored until Todium came about because of how dangerous he was, he may have been close to discovering an anti-voidlight weapon that could kill the original Odium. It would explain why he had the title originally and why it was all stripped away. Original Odium was terrified of being damaged or made vulnerable to other shards.
