5.6 Downmixing to mono
26.4053GPPEncoder specification parametric stereo partEnhanced aacPlus general audio codecGeneral audio codec audio processing functionsRelease 17TS
A monaural signal is needed for encoding of the HE AAC mono core. A simple stereo-to-mono downmixing scheme is performed after extraction of the stereo parameters. It combines equal parts of left and right channel and scales the resulting mono signal in order to preserve most of the original total power. The process is defined according to:
where the stereo scale factor, 
is defined by:
