If motherboard has SPDIF out, do you need a sound card?

No you don't need a sound card, as long as you stay all digital, meaning you pass the digital stream to an external processor, e.g. a receiver. If you use analog, however, on board sound solutions are usually poor.

Your onboard SPDIF solution is a pass-thru device, so a stream that is already encoded to DTS or DD, will get passed-thru to your receiver for processing. A PCM stream will be passed thru as just that - a PCM stream.
However, if your onboard solution has a Dolby Digital Live or a DTS Connect encoders, all audio streams from your PC will be encoded to DD or DTS.

here's my take on this.

unless you KNOW otherwise, assume your sound system is NOT bit-perfect. meaning, if you play a cd that is at 44.1k and you send the spdif (coax or opto, both are the same) to a DAC that shows the samplerate on its display, the 'bad' sound chips will still show 48k. its a 'windows thing' (for some reason) to usually force 48k, at least for audio. so one way to tell is if your true 44.1k audio comes out 44.1k on a home stereo or DAC. for a long time, I used a m-audio 2496 (envy24 chipset) card. I -knew- for a fact it was bit-perfect and not a 'resampling' type card like almost all (or all) the creative brand ones are.

I also used to like the c-media 8738 (I think that was its number). it was a very standard and cheap part, sometimes found on mobos but also sourced from m-audio (midiman). it was bit-perfect, too, but only did 44.1 and 48k - no 96k support or 24bit audio, either.

then comes the cards that support 'exotic' spdif extensions, like dts and dolby-digital. my home stereo has 'lights' to show when those modes are on the cable, as well. with any of these modes, I think that windows will NOT resample or othewise monkey with your bits. I think (but not 100% sure) that they have to stay intact, or maybe volume controlled, but that's all.

there are so many BAD sound chips out there, that you can't tell how 'honest' they are with your bits. (I used to work on DAT tape machines and so I'm used to the idea of pure bit copying with no samplerate conversions needed).

anyway, spdif != spdif. just cause its digital does not mean that someone didn't fark with the data in some intermediate stage. you have to check the chipset and just ask around.

I had SPDIF on my motherboard, but I got a sound card instead. My reason was that I picked up a lot of electrical noise from the onboard sound; I could hear the DVD-ROM drive spinning through my speakers, etc. An internal (?) sound card seemed to alleviate that.

Cush

you should NOT hear 'noise' via spdif!

you might have had a ground loop, then.

were you running coax (copper) or opto (fiber)?

proper spdif coax REQUIRES a thing called a 'pulse transformer' for 1:1 isolation and ground lifting. 99% of the sound cards on mobos don't have this, though ;( which means that opto is the safest way to avoid any hum or noise problems.

Well, I've been laboring in the dark on this for years trying to figure it out on my own, so I guess it's time to ask some questions...I've got an Envy-24 chip, hoping to get the pure pass-through, but for some reason, I continue to get 48khz sent to my receiver, and it doesn't seem like I'm getting a Dolby stream sent, either. I downloaded the latest driver from Via and tried using their config app to make sure I was set to SPDIF pass-through, and when I do that, it tells me that it defaults to 48khz unless I have it set to PCM only, in which case I can attempt to set it to 44khz. This is really frustrating to me since I've tried to get this system set up as a all-in-one package with my tv/stereo/etc, but end up having to play movies through my Xbox because I can't get a Dolby signal from my sound card (I have been able to find a way to send a 44.1khz signal, and even a 48khz signal that should be Dolby, but my receiver isn't recognizing a Dolby stream). I do have a Realtek AC850 onboard solution that I've disabled, would that do the job better of just passing the signal? Maybe my card is just fried and I need a new one.

Why can't someone just make a good soundcard? It seems there'd be a booming market for one.

the envy24 does not support DD, I don't think.

it supports 24bit 96k audio but that's it. (heh, that's good enough for me, if its a real 2496!)

I removed my envy24 card and used the onboard spdif sound and I did get DD to light up on my receiver. I forget if I was able to get it on the envy24 but I really doubt it. that card came out before DD was common, I think.

for regular 44.1 and 48k sources, I found that by setting it to 44.1 and then letting the app over-ride it (if needed) keeps the right things at the right rate. movies are always at 48k (sigh) and cd's are always at 44.1.

perhaps a 'reset to 44.1 when idle' option is there for you? that's what seemed to work for me, even though it seems a bit brute-force like.

This was an optical cable off a Gigabyte SINXP1394. The sound chip was a RealTek AC'97. I would rip DVDs to the HDD just to avoid hearing the "whine" of the disc drive through the speakers. I bought the sound card to fix the problem well over a year ago, but the motherboard and power supply quit in that machine a couple months ago. Maybe it was a bad board.

I also don't recall if I had that digital audio cable (4 pin) that runs from the DVD drive to the sound card hooked up at the time. I know I do for the ChainTech. Maybe that was the original cause of the noise.

Cush

SOMEWHERE you are getting a ground loop. or, worse, noise is inductively (by nearby proximity) induced into the sound card. but that would be weird if a digital sound card would be interfered with like that. unless they convert to audio (analog) somewhere and then back to digital. possible. many sound card designs are very sleazy ;(

that audio cable could be the problem. why do you want that, even? you can rip data even realtime over the ide bus - no need for a true spdif out from the cd player to your sound card. in fact, the spdif out from the cdrom drive is poor quality (jittery and has no ability to re-read bad blocks like a disk oriented device would). I would just snip that wire and not even bother. I never install those on my system.

so even though you used opto to go to your home stereo, you still used a copper wire to connect the cdrom to the card. I bet that was the problem. removing that SHOULD have removed the static or hum or clock noise.

my onboard sound card has humming noise, optical or coaxial. so too bad, still need to have an extra plugin card.

are you SURE its not in your speakers or audio (analog) amp?

could you be running the gains wrong? the theory is to run the wires as 'hot' as you can and then attentuate (lower volume) on the speaker or amp side.

same applies to spdif, sort of. never use volume controls on the source (pc) side - that only scales the numerical values down and gives you less resolutions than the 16bits (say) should give you. you want to run your spdif at 100% volume max (which is still not distorted) and then use the volume control on your stereo or speaker to vary. less convenient but better for the sound.

in the analog world, you'd do the same kind of thing. run the rca cable with the highest possible signal (voltage) and then attenuate down to normal listening levels in the playback system (speaker). when you do that, you get a better S/N figure.

it sounds like there are many bad sound chips out there, but you can't blame spdif for that. I still am pretty sure that digital noise is seeping in thru ground loops or even riding on the DC voltage that supplies the card or chip.

Well I don't know. I guess I've hooked up that cable since I had a Creative Labs 2x CD-ROM drive with my SoundBlaster Pro... I figured it probably wasn't being used anymore.

I do run all my volumes at 100% and adjust only at the receiver. Same with my guitar amp; I usually turn it all the way up and adjust volume with the guitar. Same principal right?

You sound like the kind of guy who can explain the technical reasons behind why my receiver goes from -100 to 0 when adjusting volume from low to high.

Cush

I have digital amp with zero background noise so I know it's soundcard's problem. Also I swapped in a $10 live! card and no noise at all. Don't know if they do any alpha or beta test at all for their product, or did this one in airport? :P

grin

yeah, that's an easy one. its 'attenuation'. its not 'people friendly' as people usually think of volume INCREASES as numbers going UP. not down

but the other way to look at this is that amps can be designed and run in 'full gain' mode (you don't vary the gain of the amp or its multiply factor (so to speak) but you, instead, lower the input level to vary the volume. some amp designs prefer to have their gain (internally) varied but some prefer to have it at a fixed level and then just vary the input level via a volume control.

so in that sense, your amp is running at 'full' all the time and you are simply lowering the input below what its 'max' is capable of. its max, by convention, is 0dB. beyond zero, you start to clip or distort. so zero is a nice number to use as a reference. remember the old tape decks that had VU meters on them? they also were zero based, mostly.

hth.

again, it seems that many do cut corners on their designs.

google 'pulse transformer' and maybe add 'DAT' to the search string. older DAT decks (that really popularized spdif) demanded these 1:1 isolation transformers for PROPER design. the signal should be balanced (no common grounds, therefore some inherent noise cancelling on the digital signal due to it being a relative 0.5v instead of an absolute ground-referenced 0.5v).

these transformers are small but not super tiny and so maybe due to cost and size, many sound cards just leave them out. but its still a BAD design to omit them in coax spdif outputs. usually there is the pulse xformer and a 75ohm carbon or metal film resistor in series to ensure that even at DC, it still 'sees' 75ohms across the cable (and also to minimize standing waves on the cable; one more noise reduction technique at the digital level).