With a 5.1 sound card, do I still need a Dolby Digital decoder?

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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.
 
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

13-170-112-03.JPG


-chris
 
macboy said:
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
 
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.
 
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......
;) :rolleyes:

Bill
 
See your point, but not yet convinced. Will surely try for myself later when I build my two HTPC's. If the soundcard has a proper layout with a good ground plane etc, there should not be any noise introduction to the analogue circuits.
And again, there is just as much internal noise from hdd's, ribbon cables etc in a mixer as a pc, so...But, will try and see for myself.
Have never tried to crank the volume all the way up on my system, 2500 watts of potential power is not fun when it is out of control...:)
 
dudster, you will inherently get noise -- i have never gotten a _perfect_ signal unless i did digital output. Its simpler too. The cleanest analog output i have ever gotten is what i use in my car -- the external creative mp3+ box. It connects via USB and is an external soundcard, since it is out of the PC, i noticed nearly 0 noise. This box has rca outputs as well as optical out if you ever end up going that route. Check it out (btw its cheaper than audigy card as well, with same results)
http://www.cix.co.uk/~davedorn/reviews/hard/sound/creativemps.htm

-chris
 
With regards to using a PC soundcard - I would always prefer to use a digital output connected to a HT decoder or reciever, second would be a dedicated outboard soundcard, lasty and least preferable an internal soundcard.

The reason I say this is (as previously stated) soundcards pick up lots of noise from all the digital circuitry in your pc not to mention the nasty switch-mode PSU.

A friend uses his pc for most music listening and has in his audio chain a spectrum analyser - even when there is no material playing there is a nasty background risidual noise on the display (very disconcerting).

In short if funds permit I recommend:

Digital output from PC (coax preferable)
HT processor + amp / HT receiver
Speakers
Air
Ears
Brain



...I've got a Denon AVC-A11SR coming tomorrow I'll try and give you some idea of how it sounds so you can decide whether or not you want to upgrade from the amp you used to have.

;)
 
More about I2S, the best digital audio transport protocol

cyr said:
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...


Can you be more specific about "some cards". Today I am looking for a card which ca output i2s to feed my dac(s) : A North Star Design Model 192 or a Perpetual technologies P3A.

Thank you very much for your answer.

Antoine.
 
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