Q. My question may sound stupid, because I'm just a beginner in audio/video. Do I need to buy a DVD player with a built-in Dolby Digital dts 5.1-channel decoder? And if so, must I also buy an A/V receiver with a built-in Dolby Digital/dts decoder? Or would this be redundant? — G. F.
A. There is no such thing as a stupid question when you're trying to 'decode' audio! No, you don't need a DVD player with a built-in Dolby Digital/dts decoder because virtually all modern A/V surround sound receivers already have internal Dolby Digital/dts decoders. The DVD player just needs to pass the Dolby Digital or dts data stream to the receiver via a coaxial or digital optical cable, and even the least expensive DVD players will do that. So it would be redundant to get a DVD player with built-in decoders (there is an exception: see below).
DVD players with built-in decoders are for use with older equipment that won't decode the digital 5.1-channel surround formats. For example, you might have a couple of old stereo amplifiers (or an old Dolby Pro Logic receiver) you wanted to use in an inexpensive Dolby Digital 5.1-channel home theater setup. As long as your old amps or receiver have line-level inputs for each amplifier channel, you could cobble together enough amps to feed the front left and right, center, and two surround channels. The DVD player with the built-in decoder will have six analog output jacks, one for each channel. Then you'd need to add a powered subwoofer for the ".1" low-frequency effects channel. You'd use the DVD players internal menu to do the proper setup for your speakers. It would be inconvenient adjusting overall volume levels, but it would work, and you'd save the cost of a new Dolby Digital/dts A/V receiver.
But if you want playback of DVD-Audio or SACD multichannel audio discs, the DVD player must have a built-in decoder for these formats because there are no receivers that will decode them (the record labels fear digital piracy so they won't provide digital outputs). Such DVD players almost always include Dolby Digital dts decoders as well.