I finally found in encyclopedia that I had goofed. His pseudonym was "Corno di bassetto".

"Shaw was also music critic until 1876 of the London papers, The Hornet, The Star, and The World. Although he knew
a great deal about music, he confessed that he did not know as much as one would suppose from his articles but, as
he said, "in the kingdom of the deaf the one-eared is king" [Shaw, II, 808] and he never ceased using his position
of influence as music critic to encourage the public to demand better standards and the musicians to produce them.
As William Irvine states, "Shaw was by no means content to tell composers how to compose, musicians how to play,
stage managers how to produce, and audiences how to feel. He also told financiers of music how to venture and
manage, and the government how to legislate with reference to musical problems. In his critical pages the English,
a placid and political people, discovered with amazement that music was a burning political issue, and might at any
moment explode into social revolution". [Irvine, 324] He wrote under the pseudonym Corno di Bassetto as he felt
that he had no name worth signing: G.B.S. meant nothing to the public at the time and he chose Corno di Bassetto
because a) he felt it sounded like a European title and b) because nobody knew what a Corno di Bassetto actually
was. [Shaw, I, 30] He was later to say though that, "if I had ever heard a note of it [then] I should not have selected
it for a character which I intended to be sparkling. The devil himself could not make a basset horn sparkle". [Ibid.,
31] These subjective, trenchant and inimitably Shavian reviews reveal a portrait of musical life in London during
the late Victorian Era and beyond and were collected and published by the Shaw scholar Dan Lawrence in three
volumes in 1981 under the title Shaw's Music. "