Digital Coax cabling

[Pinky]

I'm sure you thought twice before clicking to read this thread... how many times has this subject been brought up in the last 5 years :p... ?

I'm currently using the 6 ch analog from my sound card into my Onkyo receiver, but would like the coax to work. Tried using some spare rca stuff I had laying around but could only get sound from my front 2 L/R speakers. Before I spend money on an actual 75Ohm digital coax cable, can anyone verify that my symptoms/issue will be solved by buying one?

[kovboi]

this may be a silly question, but is your sound card set up for digital passthrough to your receiver? i'm no audiophile and i'm don't know if it would hold for all sound cards, but i've read that with audigy 2zs and some motherboard onboard audio you only get 6 channels when using a digital passthrough to the receiver for digital-audio conversion.

[Evilsizer]

quick answer no it wont solve your problem. why, my dad was using a spare cheap rca cables that came with another dvd player for the coax digital out, worked just fine. the problem seems to be in how you have it setup in your computer. remember that when using the digital output that any eax type of info can not be decoded by your receiver. only your soundblaster can do this, but i dont see a problem you can have it both ways. set your receiver to use the coax on say the dvd settings or switch which ever it may be. use that for your movies. then when gaming switch it back to say TV for the rca 5.1 or 6.1 inputs.

[Pinky]

Lucky for me one of my friends has a few spare digital coax cables, so I'll be able to test this. Would be interesting to see if this solves the problem because there's so much conflicting info on the net (rca cables are fine, no they're not/don't work, etc).

[Malpine Walis]

OK, I am going to guess that the first cable you tried was type RG-59/U. Now you want to try some RG-6/U.

Let me give you the good news first. You are getting a piece for free.

Now the bad news. There is no such thing as digital grade coax. RG-6/U has a somewhat lower signal degradation per foot. This makes it better for really long runs like from your cable modem to the router on the utility pole. But that is the only thing that is digital about it.

Seriously, you want to look into the settings on your sound card to make sure that it is transmitting the signals that you want into your amp. After all, if you think about it, why would your amp not reproduce faithfully any signal that is being passed into it?

[Pinky]

I agree MW, but through process of elimination I want to start with the obvious - so I'm going to do the testing with a true digital coax. I fiddled for over an hour with my sound card settings alone, and even at vanilla/stock/non-EAX settings I could not get anything other than front left/right. If I used a stereo 1/8" mini plug to 2 RCA adapter, I got the same front in the rear issue as the gentleman in the other thread. The hope is that my new amp is picky or that the 1/8" mono plug I'm using is somehow incorrect. Having tried everything possible with the sound card I'm likely to just live with analog if the coax cable doesn't work.

I'm 100% sure I had this same sound card working with my old Sony amp 3 years ago (when I first used a HT setup) using the 1/8" stereo to 2 RCA adapter I tried yesterday. Can't say what has changed, aside from using a different amp. I tried variations of all the amp's settings in tandem with trying variations of the sound card's settings to no avail.

One thing I was wondering about was the 'type' of signal the sound card may be sending. It is my understanding that PCM is a digital stereo signal, which may explain why I'm only getting 2 channels. But no multichannel media work either, and the amplifier only sees the 2 channel signal as a 2 channel signal (meaning it doesn't switch to various surround and DD signal processing modes). This is with direct and standard multichannel settings...

[Malpine Walis]

OK Pinkster, your evil plan to make me spew hot coffee through my nose this morning did not work (coffee not ready yet). Say this with me: There is no such thing as digital wire. Wire manufacturers will on request provide a customer with a spec sheet. Such spec sheets will rate a wire on its physical characteristics. Look for numbers such as the dielectric constant, signal loss/foot @ several different frequencies, wire gage and impedance.

However, the spec sheet will never say “true digital”, “digital ready” or any other such twaddle. That is all firmly in the realm of marketing speak. It is not relevant to the performance of the wire. It is however relevant to the ratio of the mass of your wallet before purchase vs. the mass of your wallet after purchase. Let's make an equation:

D(r)=Mw:Mw'

Where D(r) is the coefficient of digital readiness, Mw is the mass of your wallet when you walk into the store and Mw' is the mass of your wallet when you leave.

For future reference, we will call that Malpine's first law of HTPC.

As I said last night, since you are getting the wire for free, go for it dude. As Sherlock Holmes once said, “Once you have eliminated the impossible, whatever is left, however improbable must be the truth”. So you are certainly in good company. I am not sure if the master detective himself would have approved of this test but it is not like it is costing you any money.

Also, PCM is not a digital stereo signal. It is a digitized analog signal and tells you nothing about how many channels you have. To get more than one channel, you simply must have more than one signal path.

As far as how you can send multiple signal paths along a single conductor, that is done with a technique known as multiplexing. Basically, to render 5.1 sound, you would take each PCM signal and re-sample it at seven times the original rate (creating seven identical bytes out of one original byte). Then you discard six of them and interleave all the signals before transmitting them along the cable.

At the receiving end, you would then split the signal back to the original channel configuration and add the discarded bits back to each of the data streams to restore the original signals. Following that, your amp will have a bank of seven D/A converters before passing the signals on to the bank of amplifiers that drive each speaker element.

[Pinky]

You = Awesome :)

I've done some reading since I posted my last response in this thread and have 'upped' my knowledge and even figured out the likely cause (the soundcard). I have a final test I can perform (use the spdif setting in powerdvd to test multichannel playback) but haven't decided if I'm even going to bother with the digital coax now since I won't be able to do everything via the coax and the audigy 2. I get full functionality in analog and the amp would just be translating to analog anyway. So my HT receiver is just a glorified interface for my PC's speakers ;). I do have a VCR as well that the GF insists on keeping so the receiver serves some purpose.

[Pinky]

Final test still yielded only 2 channel stereo even with spdif settings in powerdvd, so the limitations are with the sound card.

[Maviryk]

Pinky, read this.

http://www.ocforums.com/showthread.php?t=427256

Also, in try Control Panel -> Audio HQ -> Device Controls -> Decoder Tab -> SPDIF Passthrough

[Pinky]

Also, in try Control Panel -> Audio HQ -> Device Controls -> Decoder Tab -> SPDIF Passthrough

Already looked for that setting, it doesn't exist in my audioHQ control panel...

[LandShark]

simple answer, NO! you can't do that!! anything NON digital sound output using digital connection (optical or coax) will ONLY get 2 channel stereo sound!! (watching DVDs will be fine as it's AC-3 format and direct pass through will just simply send the singal to your receiver for decoding)

there's ONLY 2 way to do it properly.

1. DDLive or DTSConnect. it's software base real time dolby (or DTS) encoder that will encode any of your PC sound into real AC-3 format so you can output using digital connection and directly pass through to your receiver to decode into dobly (DTS) 5.1 channel. DDLive is VERY important for anyone who wants to play games on their HDTV using a HTPC! 'cos without it, ALL in game sound will only play as a 2 channel stereo sound! with it, you'll hear the gun sound from all direction from your stereo system.

2. (and the best way, but...... :( read on....) the only hardware solution ever exist (iirc) is the old nForce2's onboard SoundStrom audio chip!! it do the same as DDLive, but on hardware/chip level. it was exist b/c M$ paid for the hefy licensing from Dobly Lab for Nvidia when it was designing the Xbox's onboard sound chip for 5.1 Dobly DIgital sound. however, the license only go for the nForce2 board too. therefore, since then (nForce3, 4, 5 series) Nvidia doesn't included the SoundStrom into any motherboard....