The 25-year-old has revealed that he had quickly made up his mind when the Blaugrana came knocking, and is looking forward to the Liga match against Real Madrid
The versatile midfielder joined the Blaugranas from Arsenal in the summer transfer window, and even though he has admitted that it was not easy to say farewell to the Premier League side, he did not need long to consider Barca's offer.
"When Barca want you, you can't say no. A train like that only passes once in a lifetime and you have to catch it," Song was quoted as saying by El Mundo Deportivo.
"I first heard about their interest in July. They talked with Arsenal, and Arsene Wenger came to tell me. It was difficult to convince Wenger and to say goodbye, because he helped me and my family a lot when I arrived at the age of 17."
The Cameroon international then looked ahead to the upcoming Clasico, and stressed that he will be more than ready if the coach needs him.
"I don't know whether I will play against Real Madrid. It is up to [coach] Tito Vilanova. We would obviously be stronger with [defenders] Carles Puyol and Gerard Pique, but I am ready for the task at hand.
"I've played against Cristiano Ronaldo before in the Premier League."
Barcelona host Real Madrid on October 7, but will take on Sevilla and Benfica before then.