In each of these devices, the analog stereo output is one of two different stereo
downmixes. One type is a stereo-compatible Dolby Surround downmix, of the
multichannel source program that is suitable for Dolby Surround Pro LogicŪ
decoding. This kind of downmix is also called Pro Logic or Left total/Right total
(Lt/Rt). The other type is a simple stereo representation (called Left only/Right only,
or Lo/Ro) suitable for playback on a stereo hi-fi or on headphones, and from which a
mono signal is derived for use on an RF/Antenna output. The difference between the
downmixes is how the Surround channels are handled. The Lt/Rt downmix sums the
Surround channels and adds them, in-phase to the Left channel and out-of-phase to
the Right channel. This allows a Dolby Surround Pro Logic decoder to reconstruct the
L/C/R/S channels for a Pro Logic home theater. The Lo/Ro downmix adds the Left
and Right Surround channels discretely to the Left and Right speaker channels,
respectively. This preserves the stereo separation for stereo-only monitoring and
produces a mono-compatible signal. In all downmixes, the LFE channel is not
included.