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Unfortunately, unlike the Dolby Digital tracks you get on retail DVDs, these DVD recorders only record in Dolby Digital 2.0. This also applies with virtually every other DVD recorder on the market, since most DVD recorders only have stereo audio inputs and the audio that comes with TV broadcasts is only mono/stereo audio.
When a Dolby Digital 2.0 sound track is output to a surround sound system, most surround sound decoders will output the left sound channel to both the front and rear left speakers and output the right channel to both the front and rear right speakers. However, very few surround sound decoders will output anything from the centre speaker unless the sound track is Dolby Digital or DTS 5.1 audio. On the other hand, if your surround sound system is capable of decoding Dolby Prologic audio, enable this feature while playing DVDs as this should enable the middle speaker, in which the amplifier outputs the sound common to both sound channels.