Words we don't find in the Psalter Hymnal. A new song. A different song. It means more than singing something different. The old song is the ongoing song of praise that creation sings to its Lord and Maker.
All nature sings that song.
The old song is a song that celebrates what God has made. The old song was sung in response to God's acts of creation. The new song is sung in response to God's acts of salvation. New deliverance brings a new song. The old song is a song for this age, a song about the present creation.