A stereo audio decoder generates a set of stereo output channels in response to a parametric audio input including signal parameters and stereo related parameters. A parameter processor generates two different set of parameters based on the input signal parameters thus up-mixing the signal parameters by altering or manipulating the signal parameters corresponding to the stereo related parameters. The two different parameters are synthesized by separate signal synthesizers to form respective stereo output channels. The signal synthesizers may be sinusoidal synthesizers, and the decoder also includes transient and noise synthesizers to generate transient and noise signal portions to be applied to the stereo output channels. Further, different transient and noise signal portions to the output channels may be provided by applying different gains based on the stereo related parameter. The two different parameters may be determined from current and previous signal parameter inputs using an input delay line.