Did all the song in the tv show Glee sing by the actors/ actresses themselves?

I love the show Glee DVD and I think the song are so beautiful but I wonder whether these songs are sung by the actors or the actresses?

A5: Most of the actors on Glee can also sing and when you see them sing on the show, that is them lip synching to their own voices. They record all the Glee covers in a studio and then they play the tracks when they act everything out and have the actors pretend to sing to them but the parts you see them singing, is really their voices.

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