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Old 12th November 2006, 07:44 PM   #1
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Default Digital Coax to 5.1 Analog?

How would i go about converting Digital Coax to 5.1 Analog? I am willing to DIY.
I am looking for the best possible sound out of my Tuner, CD, & DVD. All have coax output. Needs to get to my 6ch preamp. I need a DAC

thanks for help
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Old 13th November 2006, 09:03 AM   #2
jaycee is offline jaycee  United Kingdom
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To decode "5.1" (more correctly, AC-3 or DTS) you would need a DSP to do this. There are plenty available, the catch is that you cannot get the firmware for doing it without having a licence from Dolby etc.

The only other way to do this, is to use a PC with a software decoder and a multi-channel sound card.
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Old 13th November 2006, 07:33 PM   #3
gmarsh is offline gmarsh  Canada
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Creative DDTS-100?

If the sound quality doesn't suit your needs, haul it apart and start tapping digital audio streams inside.
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Old 14th November 2006, 03:33 AM   #4
dangus is offline dangus  Canada
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Technics SH-AC500D (with DTS) or SH-AC300 (no DTS), YAMAHA DDP-1, Marantz DP-870, Denon AVD-2000 can be found on eBay for reasonable prices. The Creative Extigy will work as a standalone Dolby Digital decoder.

Midiland ADS-4000 is similar to the Creative DDTS-100, and fetches similar amounts on eBay.

I saw a reasonably-priced home-theatre receiver that had preamp outputs; I think it was the Pioneer VSX816K.
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Old 15th November 2006, 01:07 AM   #5
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Perfect! I just run the coax through a DAC and into one of those decoder and presto? This sounds to easy...
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Old 15th November 2006, 01:33 PM   #6
Schaef is offline Schaef  United States
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Uh no, you have it backwards. The DAC is built into the decoder. You run the coax directly into the decoder and you get the analog audio out.
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Old 15th November 2006, 07:49 PM   #7
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Is there any chance of being able to diy a 5.1 DAC? Maby i can add on chips to one of those decoders?
I was looking to spend at least $1K on a DAC.

Could i split the coax signal and have a good DAC for front stereo and use one of those to get the other 4 channels?
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Old 16th November 2006, 08:39 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi Ak,
what type of signal is exported from your CD, DVD, Tuner?
I suspect they are all different.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 16th November 2006, 12:56 PM   #9
Schaef is offline Schaef  United States
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Okay, I've waited to see what everyone else says, and see where this thread goes, but I see I now have to step fully into this one.

ak_47_boy, there's a basic disconnect as to what is coming across the SPDIF signal, so, let's break it down a little bit, and hopefully this will start to make things clearer for you.

First, there's uncompressed stereo audio, such as what comes out of your CD player. This can be fed directly into a DAC and you'll get stereo sound out of the DAC. Don't worry about all of the 24/96, 16/44.1, 16/48, etc. That all just reflects bit depth and sample rate. Pretty much, any modern DAC will handle and auto detect all of these. (Unless you're into the TDA154x stuff)

Next, we get into where your confusion is. Multi-channel compressed audio, namely Dolby Digital (all variations) and DTS (again, all variations). This is very different from the above. If you feed this signal into the above DAC, if you get any sound at all, it'll most likely hurt your ears, it'll be static and junk.

What needs to happen first, is the signal needs to be fed to a decoder. This will take the signal in, figure out how many channels are in the signal, and what compression format is used. Next, it will decompress the data and break it apart into its separate channels. The next step depends heavily on whether we're talking at the silicon level or the higher up black box (theater preamp decoder) level.

At the black box, or the preamps listed above, level, the next step is that internally in the preamp the separate digital channels are then sent through internal DACs and only analog data comes out.

At the silicon level, it depends heavily on the chip used and how it was designed, but it may include three separate digital stereo outputs, most likely in I2S format for feeding into DAC chips.

Now, before you start asking for the decoder chips, stop, don't bother, you can't get them. Well, okay, you can get the chips or DSPs that are used to do the decoding, but no manufacturer will give you the code you need to do the processing, that's available only to licsensees of Dolby and DTS, and those licsenses are expensive.

So, what are your options?

First, you can pick up one of the aforementioned decoders, rip it apart, and figure out where the decoder chip is and where the separate digital output feeds on the chip are. Tap into those lines and build your own multi-out SPDIF transmitters.

Second, you could do this on a full blown computer, using a commercial application or, if you're only interested in Dolby Digital, a version of some source code can be found on the net.

Third, you could try to convince a distributor or manufacturer or Dolby Labs or DTS to give you the code needed to work with one of the processors.

My opinion? If you want to hack, try option 1, if you want quick results go with option 2, if you want to beat your head against the wall endlessly, go with option 3.

Does this help clear up things for you?
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Old 16th November 2006, 02:24 PM   #10
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Or go with option 4 and buy the seemingly license free STA310 and get clobbered by the MOQ.
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