Trying to identify new bird call

There's a new birdsong I've been hearing lately that I've never heard before. It always comes after dark, and is a bird perched high up in dense trees, so I've never gotten a look at it.

Its call is very low, slow, repetitive and mournful sounding. It's a single pitch that simply drops in octave... sort of like the sound made in WWII films of bombs dropping through the air. It's the same "dropping pitch" over and over. The best word I can think of to describe it is "sorrowful."

Just wondered if anyone has a clue what it is. I'm in Austin, Texas and have never heard it before.

Thanks!

Maybe the descending "Hoo-aw" sound of a female Barred Owl?
https://www.allaboutbirds.org/guide/Barred_owl/sounds

Great link!