Bandwidth limit of TOSLink?


#1

I’ve been looking into building a music server for the DS, and there are TOSLink cards that appear to pass 192/24-bit audio, so should be able to do DSD64 also. Is that the limit for TOSLink, or will they someday pass DSD128 and DXD?

I’d like to know because it may prove far simpler/cheaper than I2S via HDMI for comparison with USB. (Pink Faun has a suitable I2S card but it is also limited to 192kHz PCM, and seems to require Windows.)


#2

24/96 is the theoretical limit of TOSLink (it was designed for 48k) Still there are a lot of transceivers out there that, with good cables, can reliably pass 176.4k or even 192k. None (or almost none) will pass 352.8k (DXD and/or double rate DSD via DoP.)


#3

Ah, that’s interesting. The lack of ground issues and the fact that you say it’s “just a TOSLink receiver module and a wire to the FPGA” in the DS makes it appealing. Has anyone compared TOSLink to I2S in the DS using the same source?

By “almost none”, do you mean that you know of a transceiver brand/type that is capable of passing 352.8k? I did a quick search and it seems that optical transceivers used in digital audio are not particularly fast. Fibre network PCIe cards seem to be able to pass 1000Mbps or more. Uh-oh, might be heading down the rabbit hole here …


#4

That’s why I said “None (or almost none)”. I didn’t want to make a categorical statement, but I don’t know of any and I don’t know why someone would build one - it’s better bandwidth wouldn’t help with anything that’s already out there so you might as well use some other standardized interface.

A lot of the experiments I’ve heard of people doing with TOSLink against other inputs are flawed in that they leave the other input connected while they listen to TOSLink. The beauty of optical interfaces is galvanic isolation: keeping things electrically connected while listening to optical connections throws the baby out with the bath water.

The experiments I’ve done between I2S, AES/EBU, S/PDIF and TOSLink from the PWT to the DS show that all of the connections sound essentially identical if you don’t disconnect all wires except the one you are listening to. I.e. leaving everything connected means that you are masking effects of differing shielding, grounding, etc. and since the DS is relatively input jitter insensitive the jitter differences between the various inputs doesn’t matter much.

I’m certainly happy with TOSLink when I don’t need to play anything greater than 176.4k. Unfortunately I broke the TOSLink output from my PWT :slight_smile:


#5

ted, the dsd specs state 24/96 as maximum for toslink input. true? seems to be …i have a new xmos u8 converter box that gives me silence at 24/192.


#6

Yes, TOSLink was originally designed for 48k, but it does 96k reliably and 176.4k at times and 192k somewhat less often. It depends on the particular transmitter, receiver and cable. You may find that a better cable will work, I’d try an inexpensive glass cable instead of an expensive plastic one first. I don’t know what hardware you are using but you might also be bitten by DRM, each DVD, DVD-A or Blu-Ray disc can control whether it’s output will allow any sample rate over 48 (or 96k).


#7

If you have problems finding a toslink cable that will pass the max reliably, go to Sys. Concepts Inc.
They sell a 1300 strand glass toslink at a very reasonable price that has always performed flawlessly for me.


#8

Ted, My bad …i just pushed in the TOSLINK cable further into the DS …a proper click. Now I can do full 24/192 no problem. And yes, i have pulled all other connections …so my DS is fully isolated from RF noise (apart from what creeps in thru the AC Mains). The sound is spectacular and, frankly, I am not wanting for USB with all its attendant RF noise problems. Wonderful, thanks. For those interested in the USB-to-SPDIF i used, it’s here. All of $68 shipped from China to my house.


#9

Purchased the same toslink converter. Got it today. Best $50 upgrade ever. Beats curious usb with and without regen. Less grain more texture - more dimensional etc. PS should recommend that the DS be used with Toslink. Would think it would beat I2S also. It’s not a subtle improvement… Thanks for the great tip.


DirectStream better without Uptone Regen?