Battle of S/PDIF vs USB: which is better?

[amirm]

Isn't there a Coaxial vs Optical argument to investigate?

disclaimer: *plugs stuff in if it works I figure it works

Ah yes. That has been out there for so long but I don't remember any measurements backing the argument that toslink has more jitter. I will put it on my Todo list.

 

[svart-hvitt]

Ah yes. That has been out there for so long but I don't remember any measurements backing the argument that toslink has more jitter. I will put it on my Todo list.

Here are some toslink measurements:

http://archimago.blogspot.no/2013/05/measurements-toslink-optical-audio.html?m=1

 

[Jakob1863]

Around 1990 - 1994 quite a lot of measurements were done and usually measurements at the toslink outputs showed much higher jitter levels than the measurements of the SPDIF outputs of the same player.

 

[svart-hvitt]

Around 1990 - 1994 quite a lot of measurements were done and usually measurements at the toslink outputs showed much higher jitter levels than the measurements of the SPDIF outputs of the same player.

Then why are Archimago’s measurements supporting the cable agnostic view?

Did he have luck? Or are his measurements irrelevant, should he have made other measurements?

 

[Vincent Kars]

Around 1990 - 1994 quite a lot of measurements were done and usually measurements at the toslink outputs showed much higher jitter levels than the measurements of the SPDIF outputs of the same player.

What I have heard is that the 5V Toslink generation was pretty poor in the jitter department.
Todays 3V performs much better.
I once saw a measurement of a Oppo and indeed the coax performed better.
http://www.thewelltemperedcomputer.com/Intro/SQ/Toslink_Coax.htm

 

[amirm]

Here are some toslink measurements:

http://archimago.blogspot.no/2013/05/measurements-toslink-optical-audio.html?m=1

Thanks. My comparison will be toslink against coax.

 

[DonH56]

I don't have any data at hand and am far too lazy to look it up but for years I have "known" coax had lower jitter than TOSLINK, partly due to the designs of the transceivers. At a circuit level there are good reasons for optical TOSLINK to be higher noise. Audible, who knows?

For bad connectors, RCA gets my vote, though HDMI is pretty sucky as well. Of course, that's from a guy who has had to pay hundreds of dollars or more for a single RF connector, no cable attached...

 

[Fitzcaraldo215]

I don't have any data at hand and am far too lazy to look it up but for years I have "known" coax had lower jitter than TOSLINK, partly due to the designs of the transceivers. At a circuit level there are good reasons for optical TOSLINK to be higher noise. Audible, who knows?

For bad connectors, RCA gets my vote, though HDMI is pretty sucky as well. Of course, that's from a guy who has had to pay hundreds of dollars or more for a single RF connector, no cable attached...

Agreed, especially about the connectors. RCA has been banished from my system long ago in favor of the smoothly elegant functionality of XLR. Love the little click on a positive connection.

Ethernet connection is not bad, especially when the active port lights up on plugin.

USB could be a little better. Wish I didn't try to plug the rectangular end in upside down so often, though.

HDMI is terrible, except I found some cables with proprietary locking HDMI connectors years ago. I love those, and they solved all my problems.

But, Toslink? If I had a 10-20 year old DAC with only a choice between Toslink and Spdif, I would still probably go spdif without a second thought. BNC connectors on coax are not bad and far superior to RCAs. Not sonically, but in terms of pleasure in their ease of use.

As for the future, I do not see Toslink or even spdif coax as being a part of it. They are part of ancient history and too limiting.

 

[Don Hills]

... USB could be a little better. Wish I didn't try to plug the rectangular end in upside down so often, though. ...

Explained by quantum physics:

 

[Blumlein 88]

Here is a VLink USB to SPDIF converter feeding a Tact RCS 2.0. The Vlink has both coax and optical outputs and was fed the same usb signal in both cases. The Tact has both coax and optical inputs. So same clocks etc. The differences were just down to optical vs coax. Coax cable used was a meter of Audioquest VideoLink cable. Toslink was 6ft of Monoprice optical cable.

I have done the same test feeding a Focusrite 18i20 from the Vlink with the same results. Same being no difference in optical or coax. The result was actually a bit cleaner without the few sum+difference tones sticking up.

 

[Sal1950]

Explained by quantum physics:

Very informative Don, I always wondered why I had that insertion issue.
Thanks.

 

[Jakob1863]

Then why are Archimago’s measurements supporting the cable agnostic view?

Did he have luck? Or are his measurements irrelevant, should he have made other measurements?

I am not sure that i understand your question, as i was referring to measurements done roughly 20 years ago on devices comparing the TOSLINK and SPDIF interfaces while archimage did a comparison of optical cables (though i´ve to admit to only gave it a short glance).

As Vincent Kars link shows a difference between the interfaces migh be measureable even on more modern players.

But in any case it is important to remember that there might exist differences in jitter performance between the various interfaces even on the same device and that these differences might be even more pronounced on older devices.
Equally important it is to consider that the performance overall depends on the jitter (level and spectra) delivered by the source, additional effects coming from the connection and on the jitter transfer function of the DAC at the end.

 

[Jakob1863]

What I have heard is that the 5V Toslink generation was pretty poor in the jitter department.
Todays 3V performs much better.
I once saw a measurement of a Oppo and indeed the coax performed better.
http://www.thewelltemperedcomputer.com/Intro/SQ/Toslink_Coax.htm

Not sure if the performance overall is generally better in the 3V versions. Datasheets contain often only typical or max. specs on "jitter" so it might be. Uusally the older transmitters were spec´d around 20 ns typical (which is not so surprising given the requirements of the standardized interface) while the newer are often typical around 1,5 ns but with 15ns given as max.

So it is imo always the same, to be safe you have to measure....

 

[Cosmik]

Trying to assess the effectiveness of a digital link by measuring the output of a DAC is a bit of a flawed experiment. It may appear to be the 'all in one' measurement, but it is the result of multiple mechanisms, including (as mentioned before) shifting clock frequencies, random grounding schemes, stray RF, etc.

Studying the characteristics of the link itself and the mechanisms by which various DACs function would be far more useful. Then you could actually predict what was going to happen worst case rather than just sucking it and seeing.

 

[svart-hvitt]

Trying to assess the effectiveness of a digital link by measuring the output of a DAC is a bit of a flawed experiment. It may appear to be the 'all in one' measurement, but it is the result of multiple mechanisms, including (as mentioned before) shifting clock frequencies, random grounding schemes, stray RF, etc.

Studying the characteristics of the link itself and the mechanisms by which various DACs function would be far more useful. Then you could actually predict what was going to happen worst case rather than just sucking it and seeing.

Hear, hear!

 

[DonH56]

Sounds like an opportunity for Amir to get a new 'scope and compliance packages that do eye diagrams and jitter separation...

 

[Deleted member 65]

Thanks. My comparison will be toslink against coax.

Amir, make sure you have a Glassfibre optic cable when measuring and not a cheap plastic one.

 

[Blumlein 88]

JA at Stereophile measured the eye pattern of the Vlink via 15 ft of toslink plastic optical cable. Unfortunately he didn't do the same for coax, but nothing wrong with the optical result. JA reported the AP calculated jitter of the datastream as 395 picoseconds. Of course SPDIF inputs optical or coax usually are able to filter datastream jitter to lower levels than whatever is in the datastream.

 

[RayDunzl]

Amir, make sure you have a Glassfibre optic cable when measuring and not a cheap plastic one.

I would suspect that for the few feet the light has to travel the transmitting "laser" and the receiving sensor characteristics would overwhelm any differences between Glass and Plastic Multimode cores.

I could be wrong.

*worked with long-haul singlemode fiber, up to 60 miles/95 km between dispersion correction and amplification shacks, with up to 48 OC12 (10Gbit) channels (light frequencies) muxed into one fiber, often error free (even before correction) coast-to-coast.

 

[Sal1950]

I could be wrong.

NEVER!
Like you, I don't allow for that kind of miscalculation.
I thought I was wrong once, turned out I was only mistaken.