An apparatus for processing an audio signal and method thereof, the method including receiving a downmix signal including at least one normal object signal, and a bitstream including object information determined when the downmix signal is generated; extracting an extension type identifier indicating whether the downmix signal further includes a multi-channel object signal, from an extension part of the bitstream; extracting spatial information from the bitstream when the extension type identifier indicates that the downmix signal further includes the multi-channel object signal; and transmitting spatial information when mode information indicates that the least one normal object signal is to be suppressed. The spatial information is determined when a multi-channel source signal is downmixed into the multi-channel object signal. The mix information is to control an object position or an object level of the at least one normal object signal.