Credits/Sources for CTX Audio:
Most audio is mixed and mashed for the intention of originality and fluidity of it's use. Some audio clips go down several generations of remixing that can become unrecognizable from the original sources.
Audio sources range from videogames, film, Youtube videos, recordings, sound generators (such as BFXR), etc. to be mixed into something more original and not blatantly noticeable or ripped.

Example sources include:

AVP 2011
Black Mesa
CSGO
Devil Daggers
Dishonored 2
Devil May Cry 3
Flatout 2
Grand Theft Auto 5
Half-Life
Half-Life 2
Insurgency
Existing Madness Combat roster of sounds (eg. GORE and CS1.6)
Madness Project Nexus (The Unity one)
Madness Project Nexus Classic (The Flash one)
No More Room In Hell
PAYDAY 2
Portal 2
Quake
Quake 3 Arena
Serious Sam 2
Serious Sam 3
The Stanley Parable
Tekken
Terraria
Vampire: The Masquerade - Requiem
Vampire: The Masquerade - Bloodlines
DOOM 2
DOOM 2: Project Brutality (and all it's respective sources)
Soundbible.com
Freesound.org

All audio is mixed and modified with (previously NCH Software VideoPad) Audacity and DaVinci Resolve.