Interested in JUST SPDIF pass-through

[sthayashi]

I've recently upgraded my computer and as an indirect result, lost the good old NForce2 SoundStorm chip. Anyways, the old motherboard had a built-in SPDIF out, but the new motherboard doesn't.

It DOES however have a pin header for SPDIF (and I have a pinout for it, so I know the individual signal lines). I suspect that it's 5V TTL, though I don't absolutely know for certain. Now this particular built-in audio is Realtek's AC97 Codec, which I've read so-so things about, though haven't really tried it.

Right now, I'm using an M-Audio Transit for my SPDIF out needs, but I'm not happy with the driver/UI (I have to switch between PCM Out and DD/DTS pass through).

What I REALLY want is to just pass through all of my digital audio (either PCM or DD/DTS) to my receiver/decoder, regardless of bit depth or sampling frequency and without me having to switch something in software.

Now look around at circuits to convert the RealTek's possible TTL output into a 0.5 Vp-p signal or should I look into some USB to SPDIF chip?

BTW, I have no PCI slots available for sound cards, so there's no easy solution like dropping in an Envy24-based soundcard.

Any and all suggestions will be appreciated,
Thanks,
-Sthayashi

[sthayashi]

*bump* no ideas or suggestions anyone?

[seoman]

S/PDIF Digital output
there are more options like using a torx174 or 176

Infact a lot of motherboards come with a separate slot adapter wich converts the TTL levels to optical and 'real' spdif signals.
stuff like this:

[hagtech]

Can you use a USB->S/PDIF converter?

jh

[seoman]

There is in my opinion absolute no advantage in using usb as spdif output.

USB audio out can be a litle cleaner because of a lesser hf interference.
But the use the same crappy supply.
Same problems with ground levels / loops
USB can be an extra bottle neck when it comes to a constant soundstream.

onboard and pci cards are more direct and easier to approach by the software.

[sthayashi]

Originally posted by seoman
S/PDIF Digital output
there are more options like using a torx174 or 176

Infact a lot of motherboards come with a separate slot adapter wich converts the TTL levels to optical and 'real' spdif signals.
stuff like this

Rest assured I'm giving serious consideration to assemblying the circuit that Katapum has assembled.

My motherboard didn't come with the separate slot adapter (it's sold separately). Though I have a slight problem in that I don't have any spare case slots (my case has the same number of slots as my motherboard has PCI slots, no more). I was planning to either drill a hole in my case or go through one of the spare fan holes to get out to where I need.

The Torx179 looks very interesting and for <$5 USD, I could certainly do a lot worse. Judging from the specs it looks as though I could wire it directly to my motherboard's S/PDIF connector directly without any real need for resistors (or perhaps just a token current limiting resistor).

Originally posted by hagtech
Can you use a USB->S/PDIF converter?

jh

I'd love to. Can you point me to one?

The M-Audio Transit I have (a theoretical USB->S/PDIF converter) has an unfortunate fatal flaw. It will either pass-through DD/DTS or playback audio, depending on the device settings. That means that if I want to switch from listening to music to watching a DVD, I have to open up the device settings, switch from "PCM Out" to "Dolby/DTS Pass-Through" before it will work. This gets amazingly annoying quickly. So if you could recommend a USB-> S/PDIF device that can just plain pass through both PCM and DD/DTS without me having to switch it would be appreciated.


All-in-all I don't care about analog out. PCM (16 or 24-bit), Dolby Digital and DTS are all I really care about. As such, I'm not too worried about typical analog problems, such as ground loops (the computer and the receiver are both chassis grounded together anyways). I'm looking into decent power supplies as well, but the current one is a trusted manufacturer where the Vreg is no more than +/- 5%, which is good enough for digital.

Since I have background with circuits, I'm not afraid to build anything, though I'd still like to go with the easiest route. I guess I just want to make sure that I go down a path where I don't have stupid drivers attempting to resample my digital output.

[hagtech]

The M-Audio should do the job. I didn't realize you had to keep adjusting it automatically.

This is a good experiment I'll try out on my converter.

jh

[hagtech]

Well, I tried bouncing from DVD back to CD to see what happened to the HAGUSB. But most of the DVDs didn't even play (wrong video decoder). Don't remember what software I had, came stock with my IBM laptop.

But one DVD with DTS & DD played. Audio came out at 44.1k. I know this, because my CHIME only locks to redbook.

Can bounce between 48k computer noises to audio CD without any dialog boxes. It just spits out the right thing. Windows media player does not upsample the CD to 48k.

jh

[rbroer]

Originally posted by hagtech
But one DVD with DTS & DD played. Audio came out at 44.1k. I know this, because my CHIME only locks to redbook.
jh

Since 44.1kHz is not part of the DVD-Video standard, this implies the DTS & DD streams are downsampled automatically, I guess by some operatiing system sound driver. Unless I misread you, and you meant 44.1k for audio cd

[chris719]

It sounds like he played a DTS disc and got the decoded 44.1 kHz output from his computer via the DVD software. Of course, not to be confused with DTS pass through, which as you say would only work at 48 kHz. The only way to check if you can pass DTS / DD through is to connect the spdif out to an external decoder.