This post-production sound company, Twenty-First Century Entertainment (formerly known as 21st Century Sound Design Corp.) was founded by Joel Valentine (who developed The Producer's Sound Effects Library and was mentor to SpongeBob SquarePants sound designer Jeff Hutchins). They worked on exclusively cartoons, mainly ones from Hanna-Barbera and Cartoon Network, usually crediting sound editing only. The company was said to be folded into Hacienda Post/Sabre Media Studios after the end of Sym-Bionic Titan in 2011, although Joel and his uncredited team still do sound design to this very day. One of the (usually uncredited) staff members included Jeff Hutchins, an FX editor on 2 Stupid Dogs Season 1. Jeff assisted Joel and they worked closely together. While "The Producer's Sound Effects Library" is unknown in availability (though probably used by Hacienda Post, Advantage Audio and other popular sound studios for cartoons), Jeff was given both this and Joel's ADAP library from Joel himself (source: this tweet ).
- Point Break (1991) (uncredited, in collaboration with Weddington Productions)
- Yo Yogi! (uncredited; Joel Valentine is credited as a sound editor)
- Fish Police (uncredited; Joel Valentine is credited as a sound editor, in collaboration with West Productions)
- Dead in the Water (1991) (uncredited)
- The Power of One (1992) (uncredited)
- Monster in My Pocket: The Big Scream (1992) (uncredited; Joel is credited as a sound editor)
- Northern Exposure (uncredited; in collaboration with Skywalker Sound. Seasons 4-5 only.)
- The Pirates of Dark Water (uncredited; Joel is credited as a sound editor. Season 3 only.)
- Jonny's Golden Quest (1993) (uncredited; Joel is credited as the sound editor)
- 2 Stupid Dogs/Super Secret Secret Squirrel (2 Stupid Dogs segments only)
- The Halloween Tree (1993) (uncredited; Joel is credited as the sound effects supervisor)
- The Town Santa Forgot (1993)
- Joshua Tree (1993) (uncredited)
- Born Yesterday (1993) (uncredited)
- The Chase (1994) (uncredited)
- Corrina, Corrina (1994) (uncredited)
- Little Giants (1994) (uncredited)
- Unstrung Heroes (1995) (uncredited; Joel is credited as a foley editor)
- What a Cartoon! (many episodes) - Audio Services, Sound Editing
- Jonny Quest vs. The Cyber Insects (1995) - "Sound Effects Editorial"
- The World's Most Dangerous Animals (1996) (uncredited)
- Dexter's Laboratory (seasons 1-2 out of 4 only, ending with the "Chicken Scratch" short, which is also aired as part of season 4)
- Heaven's Prisoners (1996) (uncredited; Joel is credited as a foley editor)
- DNA (1996) (uncredited)
- The Beneficiary (1997) (uncredited)
- Cow and Chicken ("No Smoking" pilot only, from What a Cartoon!)
- Johnny Bravo ("Jungle Boy" and "Johnny Bravo and the Amazon Women" only, rooted from What A Cartoon!) - Audio Services
- Nightmare Ned (uncredited; in association with either Horta Editorial & Sound or Warner Bros. Post Production Creative Services.)
- The Powerpuff Girls (Seasons 1-6 only, including The Powerpuff Girls Rule!! (2009) anniversary special; in association with Hacienda Post/Sabre Media Studios, Horta Editorial & Sound, Pacifica Sound Group and Digital Soundworks.)
- Dexter's Laboratory: Ego Trip (1999)
- Samurai Jack (All seasons, but uncredited on Season 5; in association with Hacienda Post/Sabre Media Studios. Joel Valentine is credited for "Sound Editing" on Season 5.)
- Samurai Jack: The Premiere Movie (2001)
- Foe Paws (uncredited; Joel's created for Sound Editing)
- Evil Con Carne/Grim & Evil ("Evil Con Carne" pilot only)
- Codename: Kids Next Door (2001 pilot "No P in the O.O.L." only)
- My Freaky Family: Welcome to My World (2001)
- The Powerpuff Girls Movie (2002) - "Sound Editorial and Design"
- The Powerpuff Girls: 'Twas the Fight Before Christmas (2003)
- Foster's Home for Imaginary Friends (including movies "House of Bloos" and "Destination Imagination")
- Sunday Pants ("Periwinkle Around the World" segment only)
- Welcome to Wackamo (2006) (uncredited; Joel was credited as "sound editor")
- Korgoth of Barbaria (2006)
- The Powerpuff Girls Rule!! (2009)
- Chowder (TV Series) (2007 pilot only, uncredited; Joel was credited "sound effects editor")
- Sym-Bionic Titan - credited only for "sound effects design"
- Wander Over Yonder (season 2 only; uncredited; in association with Disney Television Ainmation. Joel Valentine is credited as "sound editor" only.)
- Big City Greens (uncredited; in association with Disney Television Animation. Joel Valentine is credited as "sound editor" only.)
- Primal (2019 TV Series) (uncredited; in association with Sabre Media Studios/Hacienda Post and maybe Snowglobe Sound. Joel Valentine is credited for "sound design" only.)
- Kid Cosmic (uncredited; in association with Advantage Audio. Joel Valentine is credited for "Sound effects by".)
- Unicorn: Warriors Eternal (uncredited)