Rabbi Roodyn

ה) זַמְּרוּ לַה’ בְּכִנּוֹר בְּכִנּוֹר וְקוֹל זִמְרָה

With trumpets and the sound of a shofar, raise your voices before the King, Hashem.

ו) בַּחֲצֹצְרוֹת וְקוֹל שׁוֹפָר הָרִיעוּ לִפְנֵי הַמֶּלֶךְ ה’

Play to Hashem with a harp, with a harp and a voice of song.

The Malbim says that they will sing with a harp as a way of expressing praise to Hashem for His constant goodness. The more they sing, the more He will be revealed, this is the secret of the shofar, the jubilant notes of bringing Hashem in the world as will be explained in coming days.