As Jare said. Lots of info around

https://github.com/psenough/teach_yourself_demoscene_in_14_d...

https://gargaj.github.io/demos-for-dummies/#intro/1

https://demobasics.pixienop.net/

https://github.com/psykon/awesome-demoscene

http://www.sizecoding.org/wiki/Main_Page

https://www.lofibucket.com/articles/64k_intro.html

> I suppose part of the demo scene has always been secretive and reverse engineer it if you want to know.

Not really, there's tons of info and source code out there, but fairly scattered and disorganized. It just may not be easy to know how to search for it when coming from outside. But if you can strike a conversation with a demoscener, I never saw anyone wanting to hold back secrets, on the contrary, everyone has always been excited to talk about the magic to another enthusiast like themselves (ourselves).

This 64kb intro has speech synthesis to generate the voice of the song.

https://www.pouet.net/prod.php?which=9424

More info: https://www.flipcode.com/archives/08-04-2003.shtml