This issue is discussed at length in another of my answers and is repeated here...
Your problem probably stems from the way in which the home theatre (HT) receiver is configured and, possibly, the DVD player. I assume you are using a 5.1-channel system with left and right front channels, a centre front channel, left and right surrounds, and a subwoofer or LFE channel (low-frequency effects). Even if you are using a 6.1- or 7.1-channel system with one or two rear speakers, the answer is pretty much the same.
If you can hear all of the speakers that are attached to the receiver when you use the receiver’s calibration and setup facilities, there is no problem with the amplifier output stage or the speaker wiring. There may be an issue with relative volume levels, but since you hear audio from all channels, it means that they all work.
It is important to realize that most sources provide two-channel audio only and any 'missing' audio information is synthesized from these two channels. The only exception is Dolby Pro-Logic, which was designed to encode the left, centre, right, and rear (single) channels into two channels. This protocol was developed for use on pre-recorded video tapes, which had a maximum of two audio channels.
If you are playing a true 5.1-channel source, such as a DVD encoded with Dolby Digital or DTS ES, and the DVD player is properly configured and connected to a properly-configured HT receiver, you should hear audio in all the channels. Note, however, that the volume of the surround channels is normally lower than that of the front channels because they are primarily used for effects and directional cues. Setup requires the proper connection of the DVD player to the HT receiver.
The digital output of the DVD player should be connected to a digital input on the HT receiver. If the DVD player is connected to the receiver using the left and right audio analogue outputs, it is not properly configured for many surround sound applications. You need to connect the digital audio output of the DVD player, using a coaxial or optical (Toslink) digital interconnect, to the HT receiver. The digital output of the DVD player may need to be enabled on the player, as it is often configured at the factory for two-channel analog output. The digital interconnect connects to a digital input on the receiver. The input channel must then be properly configured in the receiver. This will allow you to play multi-channel, digitally-encoded source material properly. The setup process is dependent on the model of DVD player and HT receiver – check the owner’s manuals. You may need to buy a digital coax or optical cable.
Not all DVDs have an audio track encoded in 5.1 channels. Some are formatted in the old Dolby Pro-Logic analogue format. Many provide two-channel audio only and a few older films are encoded with their original mono audio track. All other sources, except for DVD-Audio and SA-CD, provide no more than two audio channels.
The HT receiver can process a two-channel signal in any of several ways, depending on the way in which it is configured. It can reproduce the material with no alteration, providing only two-channel sound. Most HT receivers offer several audio decoding modes, including Dolby Pro-Logic, Dolby Pro-Logic II Cinema, Dolby Pro-Logic II Music, DTS Neo:6 Cinema, DTS Neo:6 Music, and proprietary ‘enhanced’ audio modes, such as jazz club, rock arena, train station, and padded cell.
All of these processes synthesize additional channels (e.g., centre front, left and right surround) from a pair of audio signals. The centre channel signal is often derived from the sum of the left and right front channels. Surround channels can be derived from the right and left channels, with a short delay, as well as the difference between the right and left channels. Regardless of the processing method, these channels are synthesized in some manner.
Since the material is synthesized, the content of the surround and centre channels is dependent on the content of the original two audio channels. A summed signal, often used for the centre channel, always contains an audible audio signal, unless the left and right channels are perfectly out of phase with one another. This is very rare. However, the surround channels may verge on the inaudible, because the level of the difference signal, L-R or R-L, may be very low. Any front channel information sent to the surround channels is low in volume and slightly delayed in time. In some HT modes and with some source material, the surround channels are effectively inaudible.
I have found that the most natural sounding synthesized audio on my system is achieved using the DTS Neo:6 Music mode. The cinema modes tend to concentrate the sound towards the centre and front of the audio image space, while the music modes have a larger image. I have found that this works well with films, even if there are ‘cinema’ or ‘film’ processing modes available. I have never found heard any proprietary ‘enhanced’ modes on any HT receiver that I care for. Most sound like larger or smaller caves (e.g., more or less echo… echo… echo).
To conclude:
- Ensure your DVD player is configured to decode and output Dolby Digital and DTS ES material on the player’s digital output (coax or optical). Since all of the audio is digitally-encoded on a DVD, all audio material will be passed to the HT receiver for decoding. The DVD player should not be decoding the source material.
- Ensure your HT receiver is configured to use a digital input (coax or optical) on the DVD input.
- Audio signals from DVDs that are encoded with 5.1-channel audio in Dolby Digital or DTS ES will be decoded in the receiver and played over the number of speakers that the receiver is configured for (e.g., 3.1, 5.1, 6.1, or 7.1). The receiver should automatically detect these formats and indicate which it is using on the front panel display. Two-channel material, including Dolby Pro-Logic on video tapes, will be processed using the decoding method you select. You should listen to the different decoding algorithms on your receiver and decide which one you like best. My preference is DTS Neo:6 Music, but your taste might be different.
Footnote: Some films provide more than one soundtrack on the DVD. These are selected in the setup options for the individual disk. The different soundtracks will sound different, so you should give them all a listen to hear what they sound like. Many 5.1 channel soundtracks are synthesized from an original two-channel soundtrack. Many of these sound better when played back as they were originally recorded, without ‘enhancements’. And finally, if you have the option of using a DTS ES soundtrack, use it instead of the Dolby Digital track because the audio quality is higher.
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