Patent ID: 8200351

Claim:
A method comprising: receiving an input signal; and downmixing, using an audio encoder, the input signal by calculating a stereo scaling factor in a group level which is definable within a stereo band using an intermediate result comprising at least one of an interchannel intensity difference parameter and an interchannel coherence parameter, the intermediate result operable to preserve the mono energy in a downmixed signal generated from the input signal; wherein the stereo scaling factor in the group level is calculated as 2 ⁢ ( A + B ) C + 2 ⁢ ⁢ D , where A = ⁢ ∑ c = 0 c total - 1 ⁢ ⁢ ∑ n = n c n c + 1 - 1 ⁢ ⁢ ∑ k = k b k b + 1 - 1 ⁢ l ⁡ ( k , n ) ⁢ l * ⁡ ( k , n ) , B = ⁢ ∑ c = 0 c total - 1 ⁢ ⁢ ∑ n = n c n c + 1 - 1 ⁢ ⁢ ∑ k = k b k b + 1 - 1 ⁢ r ⁡ ( k , n ) ⁢ r * ⁡ ( k , n ) , C = ⁢ ∑ c = 0 c total - 1 ⁢ ⁢ ∑ n = n c n c + 1 - 1 ⁢ ⁢ ∑ k = k b k b + 1 - 1 ⁢ l ⁡ ( k , n ) ⁢ l * ⁡ ( k , n ) + r ⁡ ( k , n ) ⁢ r * ⁡ ( k , n ) = A + B , D = ⁢ ∑ c = 0 c total - 1 ⁢ ⁢ ∑ n = n c n c + 1 - 1 ⁢ ⁢ ∑ k = k b k b + 1 - 1 ⁢ Re ⁡ ( l ⁡ ( k , n ) ⁢ r * ⁡ ( k , n ) ) , l and r are respectively left and right channel complex subband samples, k is a frequency channel index, n is a subband sample index, b is a stereo band index, c is a time segment, and C total is a number of desired time segments within one frame of the audio signal.