[Mark74]

If your DAC doesn't have enough Toslink inputs, some options are:

a) Buy a DAC with more Toslink input ports
b) Buy a Toslink switch box - active
c) Buy a Toslink switch box - passive

I presume (speculating here) that a DAC with multiple Toslink inputs works as follows:
....Receive light pulses, convert to electric voltage signals (logic ones and zeros), use electrical switching (mosfets or relays) to shift from one input channel to the next.

Now since the Active Toslink switch (see attached picture) has a 5v DC power input, I assume it does the same thing - light pulses to electric logic levels and use electrical switching between channels.

The Passive Toslink switch, on the other hand, physically lines up one of the incoming fibre bundles with the outgoing one.

QUESTION A:
...If you're dealing with short distance (< 1m) connections, is there anything in the physics that would make passive more robust and less subject to transmission errors than active?

QUESTION B:
...Would the DAC with multiple Toslink inputs, "likely" do its switching via the same mechanism as the Active toslink switcher? (If there are many mechanism types, I realise this question doesn't make sense).

QUESTION C:
...When using the Active switcher, the four optical feed cables stay seated in the same position, meaning the physical connection is undisturbed in the long term. With the Passive switcher, the physical rotation mechanism is operated a few times a day, and therefore potentially a thousand times a year. But if the friction is low and the materials suitable, it may just keep lining up nicely for years. Or is that a bad bet?

The above questions are just meant to elicit objective discussion of the relative merits of the device options, if anyone here has views on that.

I'd like not to focus on the anecdotal "X sounded more airy" or "Y provided better imaging" experiences, if possible, though I'll be happy to read every type of opinion offered.

 

[Strangelove424]

A) It shouldn't matter. The great thing about optical, or any other digital transmission for that matter, is it's either working or it's not. It's not like noise on an analogue cable. The music will play, or it will completely cut out. And if it starts to completely cut out, it'll be due to critical failure of the cable. One of the original benefits to optical was resilience to interference , but it's nearly impossible to get so much noise into a digital transmission that it becomes compromised. What's far more likely to happen, in my experience, is that a sensitive optical cable will make one twist too many in its serpentine run to the DAC or receiver, and start to cut out from damage.

B) No. A DAC will take optical inputs and give you analogue output, most likely RCA. With a DAC you are fundamentally translating the form of the data (converting it from digital data to analogue signal) whereas switchers are merely passing the digital data message along further upstream.

C) Well, in my personal experience optical are the most sensitive of all the cables in audio. I would prefer no moving parts.

I hope that helps, and that I understood your questions correctly.

 

[bigshot]

HDMI cables are very fussy over longer runs and kinks too. When that acts up, you end up with everything going black for a few moments while it renegotiates the handshake.

 

[pinnahertz]

A) It shouldn't matter. The great thing about optical, or any other digital transmission for that matter, is it's either working or it's not. It's not like noise on an analogue cable. The music will play, or it will completely cut out. And if it starts to completely cut out, it'll be due to critical failure of the cable. One of the original benefits to optical was resilience to interference , but it's nearly impossible to get so much noise into a digital transmission that it becomes compromised. What's far more likely to happen, in my experience, is that a sensitive optical cable will make one twist too many in its serpentine run to the DAC or receiver, and start to cut out from damage.

B) No. A DAC will take optical inputs and give you analogue output, most likely RCA. With a DAC you are fundamentally translating the form of the data (converting it from digital data to analogue signal) whereas switchers are merely passing the digital data message along further upstream.

C) Well, in my personal experience optical are the most sensitive of all the cables in audio. I would prefer no moving parts.

I hope that helps, and that I understood your questions correctly.

B). I believe he was referring to DACs with more than one optical input and on-board switching. The question was how would such a DAC handle its optical input switching. I would guess with active switching, but it's probably dependant on the specific design.

 

[Strangelove424]

HDMI cables are very fussy over longer runs and kinks too. When that acts up, you end up with everything going black for a few moments while it renegotiates the handshake.

I hate when that happens. The flatness of the HDMI connection seems to act as a lever, and pulls the pins up. I made the problem worse for myself by buying Monoprice cables with heavy sleaving. I reasoned that "if my HDMI cables are strong enough to swing from like Tarazan, well... that obviously must be beneficial somehow." It's not. Just makes the leverage thing worse.

B). I believe he was referring to DACs with more than one optical input and on-board switching. The question was how would such a DAC handle its optical input switching. I would guess with active switching, but it's probably dependant on the specific design.

Ok, misunderstood the question. I'd just add that unless the DAC has a pass-through output it will be processing the data, which will have a far greater effect on the final output than any optical switching circuitry would.

 

[pinnahertz]

I hate when that happens. The flatness of the HDMI connection seems to act as a lever, and pulls the pins up. I made the problem worse for myself by buying Monoprice cables with heavy sleaving. I reasoned that "if my HDMI cables are strong enough to swing from like Tarazan, well... that obviously must be beneficial somehow." It's not. Just makes the leverage thing worse.

I have to hold back from getting on my HDMI rant...so the short version: It wasn't technically necessary, we had a single cable solution already. HDMI was mandated by the Film industry with the advent of HD to implement copy prevention (which the pirates have completely worked around anyway). HDMI is a poorly engineered, poor mechanical design, short-sighted, ever changing, expensive and stupid hot mess.

I could go on for pages, but we're stuck with it.

Ok, misunderstood the question. I'd just add that unless the DAC has a pass-through output it will be processing the data, which will have a far greater effect on the final output than any optical switching circuitry would.

Do DACs really have optical pass-throughs? So, the on-board version of an optical splitter? Why?

 

[Strangelove424]

Do DACs really have optical pass-throughs? So, the on-board version of an optical splitter? Why?

No idea, I've never seen one. Maybe a DAC that's trying to shrug off responsibility to another DAC? A slacker DAC. Its motto: "Here, you handle it." But they're selling all sorts of strange i/o these days, so I try to leave the options open.

 

[bigshot]

Some DACs are designed for two channel only. They hand off certain codecs intended for home theater. I think my Oppo HA1 has that passthrough option. Personally, I think the whole idea of dedicated DACs is pointless. A player should be able to play everything with perfect sound. That's its job. Relegating it to just being a transport is a waste. It goes back to the old McIntosh days of having a wall covered with aqua glowing black boxes. It has nothing to do with sound quality.

 

[pinnahertz]

DAC with a pass-through: "I have one job to do. Here, you do it."

 

[Mark74]

DAC with a pass-through: "I have one job to do. Here, you do it."

I think in the Pro Audio world the pass-through could be handy for recording or "insert DSP" of the digital signal while you pump the DAC's analogue outs to the studio monitors or headphones (without having to plug/unplug cables).

Thanks for the info so far.

Sounds like Toslink cables are more brittle than I thought; but then the lack of interference and providing isolation (ground loops) is really attractive to me.

 

[pinnahertz]

I think in the Pro Audio world the pass-through could be handy for recording or "insert DSP" of the digital signal while you pump the DAC's analogue outs to the studio monitors or headphones (without having to plug/unplug cables).

Thanks for the info so far.

Sounds like Toslink cables are more brittle than I thought; but then the lack of interference and providing isolation (ground loops) is really attractive to me.

That would be an inert point, not a pass through.

The pro audio world uses AES/EBU, rarely TOSLINK if ever.

 

[Mark74]

By the way Pinnaherz, your quote:

"DAC with a pass-through: I have one job to do. Here, you do it."

really doubled me up; top humor in my book.

Now, on balance I'd rather have a digital pass-through on a pre-amp cum Dac just for possible versatility (I recall TapeIn TapeOut on old amplifiers and how that was sometimes used).
I don't think Toslink is THAT rare on pro devices - I own a couple of purely pro audio units (an "SM Pro" and a German "Mindprint") and both have SPDIF toslink and coax ins and outs but no AES/EBU port, so other brands probably have some similar stuff too.

But I'm getting off-topic here, I'm really fishing for pros and cons of Passive vs Active Toslink switchers.

And in the case of Active ones, is the technology (the laser pulse to voltage conversion) so mature that it's done by one or two common ICs so there's no real incentive to chase an expensive vs inexpensive unit?

 

[pinnahertz]

The thing about a so-called "Pro" DAC is that in most real pro applications you won't find any 2 channel interfaces, certainly not a single play-only DAC. They are kind of useless. The professional needs more channels, and records as well as plays, so there has to be an ADC as well, many times even with mic preamps ahead of it. That means the digital interface part is actually likely ADAT or MADI, both of which are designed for multichannel transport. ADAT handles 8 channels, MADI can do 32 channels at 96K, 64 at 48K. AES and Optical are limited to uncompressed 2 channels. You actually don't find a lot of AES on ADC/DAC stuff these days because of that limit, but it's included along with the S/PDIF and optical connection for versatility and connecting a two-channel device. It's on a lot of older gear too, and I have a vague memory of a multichannel device with multiple AES connections, but it's a long time ago. There are optical connections on 2 channel interfaces in the semi-pro/music market, but that's not what I meant. And the presence of balanced analog connections does not define anything as "pro".

 

[Orestes1984]

I have to hold back from getting on my HDMI rant...so the short version: It wasn't technically necessary, we had a single cable solution already. HDMI was mandated by the Film industry with the advent of HD to implement copy prevention (which the pirates have completely worked around anyway). HDMI is a poorly engineered, poor mechanical design, short-sighted, ever changing, expensive and stupid hot mess.

HDMI might not be needed for stereo audio, but its certainly needed to transfer Dolby TrueHD, DTS-HD Master Audio etc. Optical cables by their inherent design are also flimsy. Because of the nature that they work in transferring light they can also temporarily fail or be permanently damaged if the cable is tightly bent because it damages the light transfer mechanisms in the cable. HDMI doesn't suffer from this issue. I've lost count of how many TOSLINK and Mini TOSLINK cables that I've destroyed over the years simply because they're a flimsy mechanism that requires light transfer in a cable that is far too thin. Look at the size of optical fibre cables by comparison.

You can get all kinds of DACs now including some very cheap ones which will tear a lot of more expensive gear to pieces. If you piggyback something like this onto a media streamer that has 96bit passthrough you will get full 96khz passthrough, the only problem is your analogue RCAs on the end which will lose some signal quality depending on the length of the cable. This is an example of one. You get all the benefits of a high quality chip without the bells and whistles.

https://hifimediy.com/SPDIF-9018-DAC

You can build a digital system using a media box and a DAC which will poo poo on home Hifi equipment which will cost you many thousands of dollars as a source device. Problem is your output stage has to match that also. Not everyone is going to out and buy a set of speakers and an amplifier that can handle such HQ audio like that and then you reach the laws of diminishing returns as to whether you can actually hear the difference or not.

 

[pinnahertz]

HDMI might not be needed for stereo audio, but its certainly needed to transfer Dolby TrueHD, DTS-HD Master Audio etc. Optical cables by their inherent design are also flimsy. Because of the nature that they work in transferring light they can also temporarily fail or be permanently damaged if the cable is tightly bent because it damages the light transfer mechanisms in the cable. HDMI doesn't suffer from this issue.

The only reason HDMI is now necessary to transfer TrueHD and Master Audio is its position in the marketplace. It is far for the only technology capable of transmitting that sort of data bandwidth, and as I said, was not technically necessary in the first place. It was and is just a means of transmitting and connecting video and audio with one connector that includes copy protection by device identification and handshaking. We had the bandwidth already, and had single cable solutions already, and still do (Thunderbolt, IEEE 1394, and coax to name a few) . But we can't use any of them because the only connection we have on gear is HDMI.

If you're trying to say that optical cables and connectors are more fragile than HDMI, I might agree with that, but HDMI is far from robust. Next to optical it's the most delicate and fragile connector/cable system ever conceived for consumer use. HDMI cables are heavy and stiff, but plug into non-locking connectors with 19 contacts in a very small area, that are surface mounted to circuit boards. On yank in the wrong direction and that connector is snapped off the board it connects to and your device has a permanently damaged HDMI connector. Permanently, because the fix is replacement of the entire HDMI interface circuit board at a cost that approaches unit replacement. Neither HDMI or optical is field-terminatable (there was one option but it required expensive and proprietary wire and tooling), so we all buy cables that are too long and coil up the excess. HDMI and optical are both length limited, but the theoretical limits are often longer than the practical ones.

HDMI cables cannot be easily and reliably tested without expensive equipment, and failure modes are erratic and unpredictable. Optical cables are difficult to evaluate qualitatively also, but can easily be field tested in application, and failure is confined to just a few symptoms.

I frankly don't favor either method. But while we've had Toslink in one form or other since 1983, and it's typically been an option along side coax or pro SP/DIF, HDMI is not an option for the consumer in most cases, it's mandatory. Never has there been such a badly conceived and planned, and poorly engineered yet fully mandatory interconnect foisted upon the unwitting consumer as HDMI.