Appu Krishnan started his musical journey as a Keyboard player for his High School and College bands in Kerala, India. After winning several talent competitions throughout his teens, he developed a passion for programming and arranging original music. After a brief period of session work and original productions, Appu moved to Los Angeles in 2005 to attend Musicians Institute and pursue a music career in the US. After graduating from MI's Recording Program with the Outstanding Academic Achievement Award and attending the Bachelors in Keyboard Performance, he worked there as an instructor for Music Production and Sound Design. Appu also gave lectures at the Grammy Museum on Sampling during his teaching period at MI.
While producing indie artists in LA, Appu was approached by Christina Aguilera's team to arrange Strings and play synths for her single "Army of Me" from the 2012 album, "Lotus". After this successful partnership with RCA records, he went on to write Jordin Sparks's Christmas single "Christmas Time To Me". It featured a full orchestral arrangement and went on to become the title song for the hit Universal Pictures movie "The Best Man Holiday" (2013). The song charted #2 on Billboard and the movie was a top grossing hit.
In 2016 Appu co-wrote the K- pop hit "It's Me (Pick Me)" for the contestants of Produce 101 Season 2 TV show. It served as the theme song of the show aired on Mnet. The song was released online as a digital single on March 9, 2017 by CJ ENM, along with a music video starring Lee Dae-hwi as chosen center. The song peaked at #9 on Gaon Digital Chart and has sold 781,339 copies so far. According to K pop industry professionals, "It's Me (Pick Me)" was one of the most influential songs of 2016.
In 2017 the song "Another Day" co-written and co-produced by Appu was selected as the soundtrack (OST2) for Criminal Minds (South Korean TV series). The song featured the artist Yoo Hoe Seung (유회승) of N.Flying.
Other major collaborations include Greek artist Eleni Foureira, Vassy, The Jacksons, Billy Ray Cyrus, Turkish artists Sinan Ceceli and Mustafa Ceceli, Lisa Harriton, Wendy Starland, China Idol, Wei Xun, XNine, Rocket Girls 101, Producers- Shea Taylor and Brandon Friesen and Eastwest Soundsonline. Colombian artist Laura Torres's debut album produced by Krishnan won the John Lennon Award of 2015.
In March 2020, Appu co-wrote and co-produced Korean Supergroup Got 7's song "Trust My Love" in their comeback album "Dye". The album went #1 on Gaon charts and was #4 on Billboard World Albums. He also mixed "Long Black" Jus2's song from their 2019 Focus Album.
Loud Boy Music was founded in 2017 by Appu and his frequent collaborators to meet the ever increasing demands of international clientele. In 2020 Loudboy music entered into a Co Publishing Agreement with Sugar House Publishing in Finland focusing mainly on the Asian market. This venture has led to songs from K pop artists like The Boyz (Prism) and April (Now or Never) that Appu co-wrote and co-produced. In 2022, J pop group GENIC recorded the single "We Gotta Move" written by Loudboy and Sugar House writers.