Music during the thirty days of mourning for a brother and the source of the prohibition on music in mourning

Is it forbidden for a mourner to listen to music during the year of mourning for his father?

It is forbidden for a mourner for his father or mother to listen to music for the entire twelve months, and for other relatives, thirty days, because they are prohibited from rejoicing.

In the Gemara Moed Katan 26b, it is explained that a mourner should not hold a baby on his lap during the seven days because it brings him to joy and causes disgrace among people. The Tur and Shulchan Aruch in Siman 391, paragraph 1, write that specifically holding a baby on his lap, which leads to laughter, is permitted after seven days within the thirty. But in joy, a mourner is forbidden all thirty days for other relatives, and for his father and mother, twelve months. The Rema there in paragraph 3 brings the words of the Tur, who writes that the custom of the Ashkenazim is that even for those who permit a mourner to participate in a wedding, he should not enter at the time when wedding melodies are played. And although one might say about the words of the Rema that it is specifically at a wedding that it is forbidden because it is a great joy, but listening to music at home, where there is not such joy, is forbidden. Nevertheless, the consensus of the poskim (Maharsham Yoreh Deah 368 and others) is to forbid a mourner from listening to music during the twelve months for his father and mother and during the thirty days for other relatives. And the reason the Shulchan Aruch and Rema do not mention this prohibition is that even for those who are not mourners, for Sephardim, there is not such a permission to listen to music except for those who need it for their soul. And for Ashkenazim, it is forbidden in banquet halls or in regular cases, as explained in Gittin 7 and at the end of Sotah, and so the Shulchan Aruch ruled in Siman 560, paragraph 3: "And they also decreed not to play musical instruments and not to use all kinds of music and all that makes sounds of song to rejoice with them"; and the Rema writes: "There are those who say that it specifically concerns those who are accustomed to them, such as kings who stand and lie with musical instruments or in the banquet house." And those who need it for their soul, the poskim write that it is possible to be lenient.