My friend is getting married on Sunday and we are making a special song for him to be played at the wedding. They are recording the song tomorrow. Can I join them even though I hold of the first half of Sefira? Thanks.
If the song is a calm wedding song, as often played under the Chuppah, it is permitted.
The reason for this is that the principle custom to refrain from music refers to actual participation in dancing, which is the ruling given by the Magen Avraham. Later Poskim extrapolate this to refraining from music per se, but this will refer specifically to “dance music” — music that accompanies dancing.
Even if the song is for purposes of dancing (later at the wedding), there remains room for leniency, because of the mitzvah of bringing joy to the bride and groom. Many authorities rule that even while keeping the relevant half of the sefira, it is permitted to attend the wedding (of somebody not keeping the same half).
For this matter see Iggros Moshe, Orach Chaim 1:159; 2:95; Even HaEzer 1:97; Emes Le-Yaakov 493, note 465; Mekadesh Yisrael 70; Chut Shani 4, p. 380.