[Torq]

With confusing the receiver im not pointing to jitter but the receiver mistaking 1's for 0's or visa versa cause of the longer 'light on' times due to overlap of the strands light pulse arrivals.

The difference in maximum potential (i.e. worst-case-scenario) signal ToF differential within a multi-strand cable is insufficient to cause this. The typical scenario is an order of magnitude better than that. It also does not meaningfully change from a single-strand cable vs. multi-stand - assuming similar aggregate fiber diameter and materials. Typically multi-strand fibers are clad, which dramatically improves their RI vs. unclad, further reducing the potential delta.

In practical implementations, it just doesn't matter.

With higher sample rates the overall pulses time is shorter making the overlap error of longer on times more relevant. 192k seems to be on the edge of the tolerance

192 kHz is double the original sample rate for the TOSLINK spec. It is at the edges of tolerance because it needs 80ns pulses for the S/PDIF subframes, and the typical TOSLINK emitter/receiver has a rise/fall time of 30-40ns (which yields a 50% tolerance for a 96 kHz sample rate). For reliable discrimination you need the rise/fall time to be half (ideally less) of the pulse duration.

A marginal emitter/receiver (or a bad pairing - i.e. technically suitable devices, but each operating at the wrong ends of their performance tolerance/rating) may not rise/fall fast enough to maintain clean 80ns pulses. When this happens, the connection fails ... rather than 0s or 1s being misinterpreted.

You'll usually see more variation in the performance of a TOSLINK connection based on how well aligned and tolerance the sockets are than you will in the same connection using a multi-strand vs. single-strand cable.

 

[Reactcore]

I find it hard to get motivated by these arcane discussions about whether optical is better than USB or SPDIF or whatever. Any of these interfaces has a million times lower distortion than the lowest distortion headphone or speaker on the planet. When I stream a high Rez album on Qobuz, it could be traveling thousands of miles through hundreds of links, who knows how many transmitters are involved. Yet barring a technical glitch in my local internet, I get the original file intact bit by bit perfect. End of story. If you want to solve the really hard problems in high fidelity, focus on the headphone or speaker design problem. That’s where the challenges lie. Headphones are so bad a transducer and distort so badly, it’s a joke. On control your room resonances. Trying to minimize absolutely trivial amounts of digital noise on a 1 meter optical or USB link is so silly, all my CS and ECE colleagues will laugh themselves to death over it. Heck, we can receive beautiful pristine images from the James Webb telescope that is now 1 million miles away from Earth. Heck, we can detect two galaxies colliding billions of light years away releasing more energy in one collision than all the observable matter in the universe using LIGO detectors. The engineering challenges here are so formidable that they took decades to solve to make sure the measurements are not corrupted by noise. Worrying over digital noise in a 1 meter cable is really wasting time over an absolute triviality.

Just my $0.02! Feel free to ignore me and continue this discussion.

Oops you seemed to have been landed on a HiFi freak's forum

We are merely discussing why a user's streamer wont do 192k files on optical and trying to see if a different cable choice might do the trick lol

 

[muski]

Just caught up on the past few pages of this thread. It's really interesting to read a post and then compute the author's Likes/Post ratio. Rob's ratio is an enviable 3.3! Others are not so high. Hmmmm...

muski

 

[chesebert]

So firstly there is no master clock to be recovered from the SPDIF - but I digitally convert the SPDIF format into a parallel I2s like format - that is word clock, data left and data right. The word clock is extracted directly from the pre-amble, this word clock extraction only works on the fixed pre-amble so has no possibility of data related jitter, unlike using a conventional PLL based clock extraction, which relies on all transitions, pre-amble and data.

The extracted word clock then is fed to the DPLL. I should not call it a DPLL, (DFLL is more appropriate term) as phase locking is only applied initially; once initial lock is obtained, it works upon frequency only and is frequency locked to the incoming word clock - so the phase (and hence jitter) of the incoming word clock has zero influence on the generated word clock, which is generated from the local low jitter 104.25MHz fixed frequency oscillator. The DPLL ensures that the generated word clock is frequency locked to the incoming word clock, and it has a time constant of many seconds.

Meanwhile the data is fed into a micro buffer, and the data is read out from the buffer via the generated word clock, which is synchronous to the 104.25MHz low jitter fixed clock.

But I can talk as much technicalities as I like - ultimately it does not matter. The fact is that using my MSI lap-top I got identical sound quality from using optical SPDIF as using USB with Dave. USB of course is asynchronous, the data is fed to the DAC with an integer count of the 104.25 MHz low jitter clock, so no clock generation is done at all, nor any conversions from SPDIF to parallel data either. So I know the DPLL system is innately transparent. This does not mean that all USB sources sound the same as optical, as the galvanic isolation on the USB is not perfect - some RF noise can leak into the DACs ground plane from noisy USB sources via the 2pF isolation capacitance on the USB interface. But you can treat the optical input as the SQ reference, with USB either sounding identical to optical or worse, depending upon the cables and the source and how much RF noise is fed into the DAC.

Is this a really complicated way to say chord uses spdif to i2s conversion using ASRC? An ASRC block does solve the clock jitter/noise issue.

 

[Rob Watts]

So there’s no possibility of USB sounding any better than optical unless the optical output of the source is inferior to its USB implementation, leaving the only reason for using a USB input down to the 96k (sometimes 192k) limit of optical cables ?

There is no possibility of USB performing better than optical (excepting opticals 192k limit). And I use the term performing rather than sounding better as "sounding" depends upon the ear and taste of the beholder - and there is no accounting for that!

Ideally, it would be better if all USB bit perfect sources sounded identical to all bit perfect optical sources, then the source arguments would cease - in the same way when you used a noisy RF linear PSU it sounded identical to the supplied SMPS (power delivery the same) then the linear arguments would cease. It's my goal to have DACs in the future being able to accomplish this - but this actually is a very much bigger challenge than one might think at first - as the ear/brain is extremely sensitive to minute and immeasurable levels of noise floor modulation. And its changes in noise floor modulation in the analogue portion of the DAC that accounts for the SQ changes one hears from PSUs and digital sources.

No doubt after spending many years (or decades?) in the future creating such a stupendous DAC that was completely immune to RF noise from the source and the PSU, some audiophile would then criticise this DAC for not being "transparent" because they can't hear differences from sources... C'est la vie, or you can't please all the people all the time!

 

[Reactcore]

There is no possibility of USB performing better than optical (excepting opticals 192k limit). And I use the term performing rather than sounding better as "sounding" depends upon the ear and taste of the beholder - and there is no accounting for that!

Ideally, it would be better if all USB bit perfect sources sounded identical to all bit perfect optical sources, then the source arguments would cease - in the same way when you used a noisy RF linear PSU it sounded identical to the supplied SMPS (power delivery the same) then the linear arguments would cease. It's my goal to have DACs in the future being able to accomplish this - but this actually is a very much bigger challenge than one might think at first - as the ear/brain is extremely sensitive to minute and immeasurable levels of noise floor modulation. And its changes in noise floor modulation in the analogue portion of the DAC that accounts for the SQ changes one hears from PSUs and digital sources.

No doubt after spending many years (or decades?) in the future creating such a stupendous DAC that was completely immune to RF noise from the source and the PSU, some audiophile would then criticise this DAC for not being "transparent" because they can't hear differences from sources... C'est la vie, or you can't please all the people all the time!

Lucky us we have a enormously patient Rob willing to keep us all informed.. even if sometimes he has to repeat the same kind of answers

 

[Malcyg]

No doubt after spending many years (or decades?) in the future creating such a stupendous DAC that was completely immune to RF noise from the source and the PSU, some audiophile would then criticise this DAC for not being "transparent" because they can't hear differences from sources... C'est la vie

That did make me chuckle.

 

[Jawed]

And its changes in noise floor modulation in the analogue portion of the DAC that accounts for the SQ changes one hears from PSUs and digital sources.

Would a valve (tube) be more resilient against noise floor modulation?

It seems that noise floor modulation occurs due to intermodulation distortions and I'm wondering whether the distortion characteristics of a valve-based output would reduce the sensitivity of the output stage to RF noise.

 

[adrianm]

The lights on the multi core optical is dependent on the bend of the cable.

Optical is still the best for me,if it sounds fuzzy, gotta upgrade the upstream device as optical is very sensitive to psu quality and vibration. Place sorbothanes.

I mean, upgrade it to what? It's not exactly a cheap source. I'm extremely skeptical regarding anti-vibration treatment for a headphone setup.

 

[The Jester]

There is no possibility of USB performing better than optical (excepting opticals 192k limit). And I use the term performing rather than sounding better as "sounding" depends upon the ear and taste of the beholder - and there is no accounting for that!

Ideally, it would be better if all USB bit perfect sources sounded identical to all bit perfect optical sources, then the source arguments would cease - in the same way when you used a noisy RF linear PSU it sounded identical to the supplied SMPS (power delivery the same) then the linear arguments would cease. It's my goal to have DACs in the future being able to accomplish this - but this actually is a very much bigger challenge than one might think at first - as the ear/brain is extremely sensitive to minute and immeasurable levels of noise floor modulation. And its changes in noise floor modulation in the analogue portion of the DAC that accounts for the SQ changes one hears from PSUs and digital sources.

No doubt after spending many years (or decades?) in the future creating such a stupendous DAC that was completely immune to RF noise from the source and the PSU, some audiophile would then criticise this DAC for not being "transparent" because they can't hear differences from sources... C'est la vie, or you can't please all the people all the time!

For me at least a perfect reply, all I want from my CD collection is to hear as accurately as possible what’s on the disc, all of what’s on the disc and only what’s on the disc, you don’t need to go too many pages into any dedicated component thread to find cable discussions and opinions, likewise power supply options, so now close the book on sources and their interconnect cables and pursue possibly more meaningful improvements further down the chain, headphones, speakers, etc..

 

[801evan]

I mean, upgrade it to what? It's not exactly a cheap source. I'm extremely skeptical regarding anti-vibration treatment for a headphone setup.

Oh you have a good source actually. Well you're hitting a point where you need to consider isolations. I use sorbothanes on everything and it's the biggest reason I'm getting good blacks and stable imaging. Clocks are sensitive to mechanical vibration so one must use isolation not just for external dampening but internally generated vibrations too.

 

[Rob Watts]

Would a valve (tube) be more resilient against noise floor modulation?

It seems that noise floor modulation occurs due to intermodulation distortions and I'm wondering whether the distortion characteristics of a valve-based output would reduce the sensitivity of the output stage to RF noise.

OK noise floor modulations in a valve (or vacuum tube) based output stage would definitely be worse than bipolar (particularly when using my second order noise shaping OP structure) as there is little global feedback to reduce the in-band noise floor modulation. Feedback definitely reduces noise floor modulation when the cause is OP stage non-linearity.

But consider the input stage. This is more complex, as some input stage distortions are not corrected by feedback - consider a non-linear input current that modulates the voltage on the input resistors - feedback won't fix that. And here it's much more complex, and it's possible that valves with a high grid voltage swing may be more tolerant. So would I consider using a valve input stage? Definitely not; the poor transconductance of valves over bipolar (some 20 times worse) means that the virtual earth performance of the amp would be damaged, and the virtual earth impedance for the DAC is absolutely crucial to get no noise floor modulation from the DAC switching elements. This is a much bigger problem than the input stage non-linearity.

Moreover, the secret to removing RF is to use lots of localised RF filtering - and 1mm of track impedance can make a huge difference. I once did a DAC prototype (15 years ago) that used a small zero ohm SMD resistor as a shorting link on the virtual ground summing point. The design had measurable noise floor modulation; and I couldn't get rid of it. Replacing 1.5mm SMD zero ohms with a wire link eliminated the issue. So using a huge valves as a differential input would be impossible to decouple effectively over the 100kHz-10GHz bandwidth.

Valve amps sound soft and warm because of poorer damping factor, transformers in the OP stage, coupling capacitors and the increase in even order harmonics. It's possible that noise floor modulation plays a part in this too; but possible bipolar disadvantages are hugely outweighed by the benefits of allowing better RF filtering, and the elimination of OP stage created noise floor modulation. Looking at some valve amp measurements, they look horrendous - with evidence of PSU noise floor modulation, and anharmonic distortions (which sound like noise floor modulation too), so the evidence suggests that it's not better noise floor modulation that gives valve amps their warmth but simple distortions.

 

[sm60]

OK noise floor modulations in a valve (or vacuum tube) based output stage would definitely be worse than bipolar (particularly when using my second order noise shaping OP structure) as there is little global feedback to reduce the in-band noise floor modulation. Feedback definitely reduces noise floor modulation when the cause is OP stage non-linearity.

But consider the input stage. This is more complex, as some input stage distortions are not corrected by feedback - consider a non-linear input current that modulates the voltage on the input resistors - feedback won't fix that. And here it's much more complex, and it's possible that valves with a high grid voltage swing may be more tolerant. So would I consider using a valve input stage? Definitely not; the poor transconductance of valves over bipolar (some 20 times worse) means that the virtual earth performance of the amp would be damaged, and the virtual earth impedance for the DAC is absolutely crucial to get no noise floor modulation from the DAC switching elements. This is a much bigger problem than the input stage non-linearity.

Moreover, the secret to removing RF is to use lots of localised RF filtering - and 1mm of track impedance can make a huge difference. I once did a DAC prototype (15 years ago) that used a small zero ohm SMD resistor as a shorting link on the virtual ground summing point. The design had measurable noise floor modulation; and I couldn't get rid of it. Replacing 1.5mm SMD zero ohms with a wire link eliminated the issue. So using a huge valves as a differential input would be impossible to decouple effectively over the 100kHz-10GHz bandwidth.

Valve amps sound soft and warm because of poorer damping factor, transformers in the OP stage, coupling capacitors and the increase in even order harmonics. It's possible that noise floor modulation plays a part in this too; but possible bipolar disadvantages are hugely outweighed by the benefits of allowing better RF filtering, and the elimination of OP stage created noise floor modulation. Looking at some valve amp measurements, they look horrendous - with evidence of PSU noise floor modulation, and anharmonic distortions (which sound like noise floor modulation too), so the evidence suggests that it's not better noise floor modulation that gives valve amps their warmth but simple distortions.

Yes, but any half way decent valve amplifier has infinitely better measurements than any headphone or speaker I have seen. Even the 70 year old Quad II or McIntosh 275 amplifier perform far better than most loudspeakers or headphones on this planet. And if you want to really get state of the art in valve technology check out the measurements of the latest McIntosh 1100 two chassis valve preamplifier. Hi Fi News measured something like 0.0005% THD of this preamplifier. I’d like to see a headphone or speaker perform anywhere close to that, heck I’d settle for a speaker that won’t distort at 10% THD like many popular moving coil loudspeakers do in the bass. Don’t believe me? Check out the measurements of the latest Kef LS 50 Meta loudspeaker in audioscience.com — under 200 Hz, even at 85 dB, the THD of this speaker is off the charts.

Like I said, you’re all welcome to continue this discussion of USB vs optical, but it’s a ridiculously academic discussion in light of the absolutely horrible performance of headphones and loudspeakers. I’m talking of distortion that’s a million times larger. The $600 Topping DAC has linearity errors that are less than -130dB on ANY input, USB or optical or AES or I2S. There’s no speaker or headphone on the planet that has linearity error less than -60dB. Even the wonderful Quad electrostatics that I have used for 30+ years have -70dB distortion only above 100Hz and that too only for sound pressure levels around 85 dB. Over 90 dB, the Quad 63 overloads quickly in the bass, although the region above 100 Hz still performs admirably. Other moving coil speakers perform dreadfully. Ever seen what inputting a square wave produces from your average moving coil? It’s a shambles. Only a small handful of phase accurate speakers like the Quad produce a reasonably accurate square wave at the output when fed one at the input.

You’re all barking up the wrong tree here fretting over optical vs USB, and ignoring the elephant in the room: your speakers or headphones. The day we can stream bits directly into our brains through neural implants and avoid headphones or speakers will introduce a new era in high fidelity. Or someone figures out how to do a truly digital headphone or speaker that avoids any D-to-A conversion prior to it.

 

[801evan]

There’s no speaker or headphone on the planet that has linearity error less than -60dB.

DCA Stealth is THD .03% on a good part of the band which equates to -70dB

 

[adrianm]

Oh you have a good source actually. Well you're hitting a point where you need to consider isolations. I use sorbothanes on everything and it's the biggest reason I'm getting good blacks and stable imaging. Clocks are sensitive to mechanical vibration so one must use isolation not just for external dampening but internally generated vibrations too.

*puts on tinfoil hat* Do you have a link? i'm not even sure what i would be looking for or why it would make a difference in a headphone setup, but i am curious to (not) hear it for myself.