Originally Posted By: rubbersoul

I have a couple of tech related questions. Sorry if they seem unimportant or dumb.
First, I noticed on the rear panel of the 978 that there are only three optical inputs as opposed to the 990's four. I myself use all four optical inputs. I am using them with the Oppo, Roku, Sony777, and Comcast. I do know that I can eliminate the Roku and stream Netflix thru the Oppo, however I like the idea of having the four optical. Why only three?
Second, on the 990 the 7.1 channel or multi-channel is clearly labeled but not on the 978.
Does it have multi channel?

Thanks


rubbersoul,

Your dilemmas are non-existing. You don't need to ditch your Roku if you want to connect it to the 978 through the optical connector. Keep on reading to find out why.

Optical connectors otherwise known as Toslink, since it was developed by TOShiba, adhere to the S/PDIF (Sony/Philips Digital Interface Format) specification. The S/PDIF spec describes both an optical interface (Toslink) and an electrical one, often called coaxial as the cable used is coaxial (75 ohms impedance) and uses RCA connectors at both ends. Those two S/PDIF interfaces (coax and optical) essentially have the same bandwidth and are used to carry the same signals, traditionally LCPM digital data out from a CD player or a transport but also lossy Dolby Digital and DTS streams typically but not exclusively for DVD players.

Now back to the 978, on the left hand side where a column of six connectors is marked "DIGITAL INPUTS", you can see the three optical inputs on top and below there are three orange RCA connectors numbered 4, 5 and 6. Well, those three RCA connectors are the "coax" S/PDIF connectors that you can use for digital connections. So the solution is simple, you can keep using your Roku with the optical out and simply use the connector labeled "coaxial" from the Oppo BDP-93 instead of the optical one on that device. Alternately, you could do the same thing with your Comcast box if it has an RCA digital coaxial connector; I don't know the Comcast box. Your Sony 777 also has a digital coaxial RCA out connector. So in fact you have 6 S/PDIF digital inputs to choose amongst on the 978.

Many audiophiles actually prefer using the coaxial RCA inputs as they believe the electrical interface provides more speed for transients even if it is susceptible to more electrical noise. While the optical INTERFACE is much more immune to electrical noise and a fiber optic cable has considerably more bandwidth than an electrical one, the somewhat dated Toslink interface specification that defines the transceivers used that must convert the optical pulses back to an electrical signal is perhaps not as fast as it could be, arguably a little less so than a straight electrical coaxial interface.

However, as beyond 1000 and Ritz have clearly pointed out, at least for Blu-ray material that use the lossless Dolby TrueHD and DTS-HD Master Audio codecs, you should by all means use HDMI for extracting the multi-channel digital audio as you'll get the full uncompressed (lossless) digital signal, i.e. much higher sound quality over optical or coaxial (S/PDIF). The best S/PDIF interfaces out there only have sufficient bandwidth to carry LPCM up to 192KHz/24bits (in stereo only) or plain Dolby Digital and DTS but not the two new high resolution multi-channel audio codecs mentioned above that Blu-rays typically use.


Edited by jam (04/10/12 04:33 PM)