February 2002

Connections: Six-Channel Analog Inputs

Have you ever wondered what that bank of six RCA inputs on the back of your receiver is for? It goes by various names such as "Six-Channel Direct" or simply "5.1 Direct" or "External Processor." While these inputs may go by different names, they basically all do the same thing and that is to route signals directly to the preamplifier section of the receiver. The receiver will then act as a volume control for those signals and provide amplification for the left, right, center, left-surround, and right-surround speakers and output a line-level signal for a subwoofer.

Most people will never use these inputs as they normally have a digital connection to their receivers, which carries all the necessary signals from their DVD player for Dolby Digital, DTS, and stereo playback. Other sources such as VCRs, tuners, and tape decks are connected via standard stereo inputs. However, there are instances when six-channel inputs are useful or even necessary.

Upgrading a "Digital Ready" receiver

Before Dolby Digital and DTS became as commonplace as they are now, they were an expensive option available only on top-of-the-line receivers or on expensive separates. However, many receivers that did not have digital decoding built into them had six-channel inputs, which was a feature that was said to make them "Digital Ready." By using these inputs, it was possible to obtain discrete digital sound by purchasing an external decoder or a DVD player that performed its own digital decoding. These components output 5.1 channels of analog sound.

However, external digital decoders and DVD players with built-in decoders were also quite expensive at that time and relatively few people upgraded their systems in this way. For those of you who still have digital-ready receivers, DVD players with internal Dolby Digital and DTS decoders are now inexpensive. Therefore, this could be a cost-effective upgrade, especially if you are already considering the purchase of a new DVD player. There is also the option of adding an external digital decoder, although these are fairly rare and are available mainly on the used market, so this may be less of a viable option.

Considering that receivers with Dolby Digital, DTS, and Pro Logic II are now available for only a few hundred dollars, it probably makes more sense to scrap your old receiver and simply purchase a new one. Nevertheless, if you have a digital-ready receiver that contains high-quality amplifiers or if you really want to upgrade that old receiver, there are the aforementioned options.

Connecting an external decoder is relatively straightforward. Simply connect the digital output of the DVD player to the external decoder via a coaxial or TosLink cable and then connect each of the six analog outputs of the decoder (you will have to use six analog RCA-type cables!) to the corresponding inputs on your receiver. A DVD player with built-in digital decoding would be connected in a similar fashion by using its six analog outputs and connecting them to the corresponding inputs on the receiver.

Upgrading a system to the latest multichannel audio formats (SACD and DVD-A)

While six-channel analog inputs used to be the domain of inexpensive digital-ready receivers, they are now provided on most receivers even though nearly all of them possess decoding of both Dolby Digital and DTS. In fact, recently it seems that six-channel analog inputs are actually more common on more expensive receivers than on budget receivers -- the opposite of what was previously the case. So what brought about this change? The introduction of the DVD-A and multichannel SACD audio formats necessitated the inclusion of these analog inputs on receivers and processors to allow the user to play back these new formats.

The reason for this is that multichannel SACD and DVD-A players do not output the digital data streams of the new high-resolution formats. Because of copyright-infringement issues, the digital outputs of these players were limited to Dolby Digital, DTS, and PCM (16-bit CD) data streams as with any other DVD or CD player. The multichannel SACD and DVD-A signals are only available through the six-channel analog outputs. Anyone who wants to listen to multichannel SACD or DVD-A discs must have a compatible player and a receiver, processor, preamplifier, etc. with six-channel analog inputs.

Some multichannel SACD or DVD-A players have built-in Dolby Digital and DTS decoders that can output six channels of analog sound. Otherwise, a digital connection to a receiver or processor will still be required to listen to Dolby Digital and DTS soundtracks.

Some limitations

One complication when connecting a multichannel source to the six-channel analog inputs of a receiver or processor is that this normally bypasses the digital signal processing, which controls such things as bass management and channel delays. Therefore, if your receiver is directing bass away from smaller speakers in your system or if you have delays set for your surround speakers, these features will no longer be available to you.

Some DVD players incorporate channel delays and bass management for Dolby Digital and DTS decoding, but this is much less common for DVD-A and SACD playback. However, there is the option of adding an external bass management device such as the Outlaw ICBM that was reviewed by Home Theater & Sound senior editor Jeff Fritz on our sister-site SoundStage!. This device allows you to redirect bass from all channels to one or more subwoofers and costs an amazingly low $249. Other than the Outlaw, there are few other six-channel bass-management devices that come to mind, especially at such a reasonable price. Additionally, the ICBM’s bass-management features are far more comprehensive than the rudimentary bass management offered on most players.

One more thing

While the six-channel analog inputs on most people’s receivers will never be used, they do offer a viable upgrade option for older digital-ready receivers and are currently the only common method to take advantage of the multichannel music tracks of SACD and DVD-A discs. However, they can also be used as an additional set of stereo inputs by utilizing only the left and right channels if you run out of standard inputs. An interesting side note to this is that sources connected in this way may actually sound better because this normally bypasses the DSP of the receiver or processor, which could degrade sound quality due to the analog signal being converted to the digital domain and then back again. However, this also means that because the signal is channeled directly to the preamplifier section of the receiver, DSP-controlled features such as bass redirection will usually not be available. Consequently, this type of setup would not work well for a small subwoofer/satellite system where the subwoofer is connected to the LFE output of the receiver.

...Roger Kanno
roger@hometheatersound.com

• Go Back