A method and circuit for deriving a set of multichannel audio signals from a conventional monaural or stereo audio signal uses an auxiliary multichannel spectral mapping data stream. Audio can be played back in stereo and multichannel formats from a conventional stereo signal on compact discs, FM radio,...http://www.google.com/patents/US7792307?utm_source=gb-gplus-sharePatent US7792307 - Multichannel spectral mapping audio apparatus and method
