With a 5.1 sound card, do I still need a Dolby Digital decoder? - diyAudio
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Old 12th March 2004, 07:31 PM   #1
JCoffey is offline JCoffey  United States
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Default With a 5.1 sound card, do I still need a Dolby Digital decoder?

If I were to build a HTPC, and use a Create Audigy 5.1 sound card, can I connect the outputs to a 5 channel amp, or do I still need a digital decoder?
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Old 12th March 2004, 07:44 PM   #2
macboy is offline macboy  Canada
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Yes, you can use the 5.1 channel analog outputs of the soundcard. With most cards, you would requireDVD playback software that has DD (and optionally dts) decoding capability. With the Audigy though, you can just tell the software to send the DD stream to the S/PDIF port, and then enable the setting int he Audigy drivers that tell it to decode the DD stream into 5.1 sound. One caveat: I do not know if the audigy decoding allows you to turn off or adjust the dynamic range compression. If not, then it will probably be on by default. That isn't necessarily bad (especially if you have small speakers) but you won't get the full impact of the soundtrack. Not all DVD software decoders will allow you to adjust this either.

Also be aware that the sound quality will not be great. The inside of a computer is an electically noisy place, and some of that noise invariably gets into the audio signals. Sending the DD data stream to an external decoder will probably provide significantly better results.
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Old 12th March 2004, 08:07 PM   #3
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most of the decent motherborad nowadays have onboard spdif output, so you do not even need an extra soundcard. for example, in my pc i use the onboard spdif coaxial output going into my receiver, which decodes ac-3 and dts. this _is_ the best way to go, if you take analog signals from the pc you will invariably get noise. i use long runs in my room and i had about 75ft of cable (tons of hum). after building a balanced line driver it went down considerably however it wasnt perfect until i just used straight digital output -- used cheap radio shack 75ohm video cable and it works like a charm

go to newegg.com and browse the motherboards with the nvidia ultra-400 mcp-t chipsets, they have very very nice audio onboard.
for example, this motherboard has onboard apu with spdif input and output coaxial, as well as optical toslink output

Click the image to open in full size.

-chris
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Old 12th March 2004, 08:33 PM   #4
cyr is offline cyr  Sweden
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The *best* solution IMHO is to get the 6 or 8 discrete channels digitally from the soundcard to external gear. This is easy with some (like the good old SBlive! that has 4 separate S/PDIF outputs on a header).

Some cards have I2S signals that can be tapped and sent outside...
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Old 14th March 2004, 09:37 PM   #5
rehgf is offline rehgf  Finland
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Some related sites I have collected on the subject:

S/PDIF and 5.1 audio
http://www.andrewkilpatrick.org/mind/spdif/
SB Live misc info
http://w1.910.telia.com/~u91003452/l...live_start.htm
SB Live Value to SB Live 5.1 conversion and lots of info
http://users.andara.com/~cquigley/sb.html
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Old 1st April 2004, 11:50 AM   #6
b<ben>n is offline b<ben>n  Australia
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this is not realy answering your question but if your building a htpc then have a look at www.mini-itx.com there some realy good boards.
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Old 1st April 2004, 12:03 PM   #7
b<ben>n is offline b<ben>n  Australia
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this is not realy answering your question but if your building a htpc then have a look at www.mini-itx.com there some realy good boards.
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Old 1st April 2004, 03:10 PM   #8
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Quote:
Originally posted by macboy
Yes, you can use the 5.1 channel analog outputs of the soundcard. With most cards, you would requireDVD playback software that has DD (and optionally dts) decoding capability. With the Audigy though, you can just tell the software to send the DD stream to the S/PDIF port, and then enable the setting int he Audigy drivers that tell it to decode the DD stream into 5.1 sound. One caveat: I do not know if the audigy decoding allows you to turn off or adjust the dynamic range compression. If not, then it will probably be on by default. That isn't necessarily bad (especially if you have small speakers) but you won't get the full impact of the soundtrack. Not all DVD software decoders will allow you to adjust this either.

Also be aware that the sound quality will not be great. The inside of a computer is an electically noisy place, and some of that noise invariably gets into the audio signals. Sending the DD data stream to an external decoder will probably provide significantly better results.
I am not sure this statement is all correct. If you consider that the sound was recorded on a multichannel mixing console, most likely all digital. It was recorded on a digital tape machine or on harddrives. It was then mixed down to a 7.1 or 5.1 or whatever format on a digital mixer. During this process, it was surely monitored through the mixer's analog outputs. What does this mixer do so rigth that the pc can't? The mixer is just one big piece of a computer where the console is the remote control and all the electronics are in a rack or two. Not really sure that the pc is such a bad sound provider. I just had my nice Denon AVC 3802 stolen and plan to buy a shuttle pc with a creative audigy pro soundcard as a base for my home cinema. Let the soundcard output straigth into the ICE power amps. Have anybody done any A/B tests to confirm that a normal pc with a decent soundcard falls short of a decent home cinema reciever. I am not too sure, lots of processing going on inside a reciever too...

Just a thougth...

:-)

BAF
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Old 1st April 2004, 04:05 PM   #9
macboy is offline macboy  Canada
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Quote:
What does this mixer do so rigth that the pc can't? The mixer is just one big piece of a computer where the console is the remote control and all the electronics are in a rack or two. Not really sure that the pc is such a bad sound provider.
It has nothing to do with what the PC can or cannot do. My statement referred to the fact that the inside of a PC is riddled with EMI and RFI noise radiating from various sources. You don't use shielded cables inside a PC because the metal case takes care of shielding the outside world from all that noise. Anything inside the case (like a soundcard) is subject to the noise though. This noise can, and usually does, make its way into the analog outputs of soundcards.

Try this: plug the analog output (like headphone/speaker output) of the soundcard into your audio system. Turn the PC volume all the way down and click mute. Now, no audio should be produced by the PC. Turn up the volume on your audio system so that you can hear the background noise. Do some stuff like opening a large file (to cause disk access), access the network, etc. You will almost definitely hear a lot of garbage. If you switch your audio system to a CD player input and put the CD on pause, you will not hear as much background noise.
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Old 1st April 2004, 04:26 PM   #10
netgeek is offline netgeek  United States
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Another thought:

Check out the Creative DDTS-100 external decoder. It does DD, DTS, Neo-6, and a few others I believe and is meant to be used with powered PC-type speakers.

Perhaps a neat DIY project would be to rip the thing apart (they only cost US$100 or so) and use it as the decoder section of a decent homebrew A/V switch, preamp, volume control, etc. using decent components. You end up with S/PDIF in and whatever-you-want out (e.g. se/differential, line level, etc.) Hey, you could even add your own bass management if you wanted......

The manufacturers won't sell the chips without licenses, but nothing says you can't buy one of these (or any A/V receiver) and hack it any way you want to suit your system......


Bill
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