Section 37 of RA 8491 specifies how the Philippine National Anthem should be sung. Violators [singers of famous Pacquiao fights such as Martin, Charice, and more recently, Arnel] of this statute insist on their artistic freedom, which, loosely construed, means they can sing the anthem according to their own arrangement. The National Historical Institute has been continually chiding these artists but has yet to prosecute anyone.
Of course Arnel Pineda has a great voice, no question about that. And, his rendition of the national anthem was spectacular. But the point is, this is not just an ordinary song he is recycling, remixing or covering. There is a law governing the correct rendition of this song. Thus, the law itself is a curtailment of one’s artistic freedom, like most other freedoms we enjoy, that are never absolute.