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carmangary 24th April 2007 08:32 PM

S/PDIF to 8 channel analog
Hi. I am trying to rig something up to control some laser show hardware. I need to end up with 8 analog channels less than 30Khz. Since this falls within the audio range I am thinking of using a multichannel WAVE file to control the channels.

I would like to use the SPDIF output of a soundcard and build some type of circuit that converts the 8 channel SPDIF output to 8 analog signals. I would assume that the same type of thing has already been done for obtaining 7.1 audio. Does anyone know of a schematic or circuit that I could look at as an example? I have found circuits for 2 channel (L & R) but I need to see a multi channel example. I am not a good electronics designer but I can usually following a shematic if one is presented.


jaycee 24th April 2007 11:07 PM

Anything better than stereo over SPDIF is usually a compressed data stream such as AC3 or DTS, which is totally unsuitable for your needs really.

better to forget SPDIF and simply get a soundcard with many analogue outs. I've only seen them with up to 6, though.

carmangary 25th April 2007 07:24 AM

I was a bit afraid of that. Why do you say that the AC3 or DTS is unsuitable? Is it because of the losses due to compression? Or some other reason?

rfbrw 25th April 2007 09:59 AM

ADAT. 8 LPCM channels over a single toslink cable. Optical rx, ADAT decoder, 8ch DAC and a few opamps and you are done.

weissi 25th April 2007 11:01 AM

ADAT IC's ==> Wavefront Semicon

weissi 25th April 2007 11:03 AM

ADAT IC's ==> Wavefront Semicon

oops, since you do not need high quality, I'd say you'll try it first with a cheap 8CH soundcard....

carmangary 25th April 2007 02:22 PM

You lost me with the ADAT stuff. I want to send data from a PC not a tape recorder. Did you misunderstand me or am I misunderstanding you?

Also, I am looking for an inexpensive solution.

weissi 25th April 2007 02:31 PM

You can also use your PC to send ADAT, most professional Soundcards now support this standard. ==> e.g. EMU1212m. Beside that, which interface do those lasers have? imho another problem is that AC3 doesn't handle all channels with the same bandwith. some more Information please....

dwk123 25th April 2007 03:16 PM

I'm not quite sure I see the part of this problem that you're trying to solve via a 'complicated' transmission mechanism. There are many soundcards out there that already have 8-channel analog outputs without the need to do anything further. What is driving you towards wanting to use SPDIF or some other 1-wire protocol and an external converter? Is there a long wire run you need to handle or some other constraint in place?

The Emu 1212m outputting ADAT to a Behringer ADA8000 would be relatively inexpensive as far as external solutions go, but still over $300. A plain-vanilla 8-channel soundcard will run you somewhere between say $80 and maybe $250 depending on the specifics of OS, quality etc you need to work with. The OEM M-Audio cards at newegg or the Azentech X-Meridian are examples of things that should work reasonably well.

carmangary 25th April 2007 03:31 PM

The laser board needs 6 channels of 0-5v. I could use a slightly modified 5.1 soundcard to do what I want (and I actually already have) but I want 8 channels so that I can put stereo music on channels 1&2 to have a completely synchronized sound/laser experience. I haven't seen a cheap soundcard with 8 analog outputs, though. The one I have is CM106 based and does allow 7.1 audio but only through SPDIF. That is why I was asking about the SPDIF decoder. But, if AC3 won't work for me then I will abandon that idea.

I am not familiar with the ADAT format. I'll have to look into it more. Are there any relatively inexpensive cards that can send this format? A USB soundcard would be even better so that I could plug it into a laptop.

Thanks for all of your help and ideas.

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