Hipotecar literally means "to mortgage," as in to put up property as collateral for a loan. It's a strong and somewhat formal word not commonly found in everyday song lyrics.
In this song, Antonio Orozco uses it metaphorically in the line "Sería capaz de hipotecar mi voz" (I would be capable of mortgaging my voice). This powerful imagery conveys a deep level of sacrifice and commitment, suggesting he would give up his very essence or means of expression for the person he loves. It's a unique and memorable way to express profound devotion.
Antonio Orozco built this song out of one vow, sung again and again as its own chorus: "Lo que, lo que tu quieras soy" ("Whatever, whatever you want, I am"). Each verse pushes that promise into a stranger shape - "Un payaso sin pintura" ("A clown without makeup"), "El soldado al que le ordenan disparar" ("The soldier they order to shoot") - until it stops sounding like romance and starts sounding like surrender.
The bridge keeps raising what he is willing to give up: "Seria capaz de regalar mi edad" ("I'd be able to give away my age"), "Seria capaz de hipotecar mi voz" ("I'd be able to mortgage my voice"). By the last chorus he has nothing left to offer that he has not already handed over.