[Soundproof]

I'm getting high-resolution audio out of my Mac computers via USB or the TosLink Optical minijack.

However, I have a pair of speakers that accept a digital coax S/PDIF signal. I have tried a TosLink Optical to coax S/PDIF converter (inexpensive).

What other options do I have? Anyone have experience with converting digital to digital in this manner.
I am, of course, looking to achive bit transparency from source to loudspeakers.

 

[Gatsu]

An inexpensive converter should do the job pretty well. There is no difference between the signals really, just one is optical and the other electrical. The format of the signals is exactly the same.

http://en.wikipedia.org/wiki/S/PDIF

If you take a look at the epanorama link down the bottom it should have some converter circuits.

 

[Soundproof]

Quote:

Originally Posted by Gatsu /img/forum/go_quote.gif An inexpensive converter should do the job pretty well. There is no difference between the signals really, just one is optical and the other electrical. The format of the signals is exactly the same. http://en.wikipedia.org/wiki/S/PDIF If you take a look at the epanorama link down the bottom it should have some converter circuits.

Hi. Thanks. I know it's S/PDIF in both versions -- I wanted to plumb the forum as to whether there's a risk of reducing bit transparency unless one uses a specific converter.
Also - I wonder whether anyone knows of a connection that would draw on the USB or Firewire outs, and deliver an S/PDIF coax signal which I could then run straight without any conversions.

 

[error401]

You might want to think about pulling the digital signal out to coax in your Mac. Since the signal is identical you can pretty much just take the data line going into the optical module out to some coax or a custom coax jack. You should impedance match to 75Ω with a pulse transformer, but this is not strictly necessary. This would be the best way to get coax out of the Mac, but as it requires modifying the computer, it might not be feasible for you.

Another option would be to build or purchase a device that accomplishes the same goal, but with the optical as input instead. You'd need a 5V power supply, optical receiver module, and some kind of buffer as a line driver. Really a rather trivial circuit, and likely what you've already got. This might introduce some (possibly significant) jitter into the system, but shouldn't cause a significant increase in bit-error rate. It's extra, unnecessary conversion though. If you don't have one with an impedance matched output you might improve things slightly by adding the pulse transformer, but I imagine this would only make a difference for poor transmission lines or receivers.

A more complicated option would be to do something similar, but use an SPDIF transceiver in the circuit instead of just a plain buffer to lock the signal and regenerate it. This would hopefully reduce the jitter problems, but it's a lot more complicated to implement and I don't know of any commercial products. A chip like CS8427 would be appropriate for this.

There are USB -> SPDIF interfaces available for sale at various places. They consist of a USB receiver like the Burr Brown PCM2707 and an SPDIF encoder/transmitter like the CS8406. Check out the UD-10 that's inexpensive and seems to be well liked as a transport. I think you'll find that the jitter will be much worse than just converting the TOSLINK to coax, however, as USB doesn't provide any good way to clock the signal, it's even worse than SPDIF in this respect.

In any of these cases I don't see how the bit-error rate would ever be significantly increased, jitter would be the main concern with any of these options. The best of them would be to pull the logic directly off the sound board, followed by running it through a good quality receiver to reclock and regenerate it.

 

[Soundproof]

Thanks. I really appreciate this.
Think I'll go the modifying route - the Mac that will be managing my music, etc., will be a dedicated unit -so modifying it shouldn't be a problem. Will check into this ASAP.

As you say, the point must be to have as few conversions as possible. I'm going to have the computer connected to my music server (ReadyNAS) via Ethernet, and then pipe the music from the Mac directly to a pair of digital BeoLab 5 speakers (daisy-chained).

 

[grawk]

I would highly recommend AGAINST modding your mac. You'll invalidate any warranty instantly on doing that, and there are a number of less expensive and equally reliable ways to get spdif out.

 

[Soundproof]

Hi Grawk,

Oh, you should see my Macs. I have owned Macs since 1985 and have very rarely had any warranty issues -- and I'm willing to take the chance here. Have several computers I'm not using actively now that have processor speeds that would be more than adequate to manage the task.
Though also looking forward to October, the Leopard lunch and the new (rumored) Mini which is supposed to be specifically targeted at the mediacenter market.

I don't think getting the signal going into the optical module would be expensive, and I am attracted by the notion of going to the source, with no in-betweens, to get the S/PDIF.

But do suggest alternatives, if you want.

 

[krmathis]

You could buy an external DAC or converter box which take optical digital input and output coax digital. My Electrocompaniet ECD1 have this option, and I am sure other devices have this option as well.

 

[Soundproof]

Quote:

Originally Posted by krmathis /img/forum/go_quote.gif You could buy an external DAC or converter box which take optical digital input and output coax digital. My Electrocompaniet ECD1 have this option, and I am sure other devices have this option as well.

Thanks, yes - I'm aware of this, but I would like to avoid going via optical, since the s/pdif signal is available straight from the tap, so to speak. There's a lot of discussion back and forth as to whether these conversions degrade the signal by introducing jitter - by going direct from the source that discussion is closed (at least I'll only be dealing with the jitter from the media, though by reading from harddisk and using a wordclock it's possible to eliminate that).

===

Have received suggestion concerning card and interface that will also solve my requirements for a wordclock. And I won't have to mod the Mac.

http://www.mediaspec.co.uk/detail_ne...RME&stock=1116