  A geometrically-motivated method for primary-ambient decomposition is
proposed and evaluated in an up-mixing application. The method consists of two
steps, accommodating a particularly intuitive explanation. The first step
consists of signal-adaptive rotations applied on the input stereo scene, which
translate the primary sound sources into the center of the rotated scene. The
second step applies a center-channel extraction method, based on a simple
signal model and optimal in the mean-squared-error sense. The performance is
evaluated by using the estimated ambient component to enable surround sound
starting from real-world stereo signals. The participants in the reported
listening test are asked to adjust the audio scene envelopment and find the
audio settings that pleases them the most. The possibility for up-mixing
enabled by the proposed method is used extensively, and the user satisfaction
is significantly increased compared to the original stereo mix.
