 Independiente marked Arjona 's fourth collaboration with Torres . The latter was a composer and producer , also receiving background @-@ vocal credit . The musicians first worked together in 2005 , when Arjona released his tenth studio album ( Adentro ) . He stated that he first " tested " Torres by sending him the " hookiest and darkest tracks " on the album : " Acompañame A Estar Solo " and " <unk> " . Torres then " went all out on the first demo , hiring a full band that included a string orchestra " . In Quién Dijo Ayer ( 2007 ) , Torres produced the singles " Quién " and " Quiero " and provided background vocals on the remastered versions of Arjona 's past hits . In 5to Piso ( 2008 ) , Torres produced several tracks ; one was the lead single " Como Duele " , considered Arjona 's " biggest hit in years " by Jason Birchmeier of Allmusic . 
