Cleaning up USB signal for DAC

[miksu8]

Hi, my first post here

 

I'm owner of Chord Mojo DAC and probably upgrading to Hugo 2 and using laptop USB as source.

 

My questions are about cleaning up USB signal with additional device between source and DAC:

 

1) Chord provides error correcting ASIO drivers so is it still possible that jitter, if any created, can cause audible errors? Should any such driver always eliminate the effect of jitter?

 

2) In case where jitter doesn't matter can a reclocking "USB purifying device" make sound any better? Can reclocking USB signal do anything else but eliminate jitter?

 

3) I read that RF noise from USB source can make almost any DAC sound worse and it should be filtered out. So how can this be achieved? Galvanic isolation which is breaking the ground signal of USB?

 

4) If DAC doesn't draw power from USB, as Chord doesn't, cleaning up the power should not make any changes to sound?

 

5) In addition to jitter and RF noise, USB cable can pick up some noise too? So I guess proper shielding of cable eliminates that?

 

Sorry lots of questions but I'm just interested in the theory how things work. And trying to choose right device for my setup. Where I live we have practically only Ifi devices, so probably choosing from them (iUSB3.0, iSilencer etc).

 

I posted some of these questions to head-fi too but didn't get any answer there.

[ElviaCaprice]

Hi, my first post here

 

I'm owner of Chord Mojo DAC and probably upgrading to Hugo 2 and using laptop USB as source.

 

My questions are about cleaning up USB signal with additional device between source and DAC:

 

1) Chord provides error correcting ASIO drivers so is it still possible that jitter, if any created, can cause audible errors? Should any such driver always eliminate the effect of jitter?

 

2) In case where jitter doesn't matter can a reclocking "USB purifying device" make sound any better? Can reclocking USB signal do anything else but eliminate jitter?

 

3) I read that RF noise from USB source can make almost any DAC sound worse and it should be filtered out. So how can this be achieved? Galvanic isolation which is breaking the ground signal of USB?

 

4) If DAC doesn't draw power from USB, as Chord doesn't, cleaning up the power should not make any changes to sound?

 

5) In addition to jitter and RF noise, USB cable can pick up some noise too? So I guess proper shielding of cable eliminates that?

 

Sorry lots of questions but I'm just interested in the theory how things work. And trying to choose right device for my setup. Where I live we have practically only Ifi devices, so probably choosing from them (iUSB3.0, iSilencer etc).

 

I posted some of these questions to head-fi too but didn't get any answer there.

I used a Chord Hugo and soon to be alternative, 2Qute or Hugo2. On the Hugo's (non TT) you will need galvanic isolation. At this point I highly recommend the Intona, that one component is a given regardless which direction you go. There are two different routes to streaming to your Chord DAC from a controlling PC that I would recommend.

1. Ethernet with Renderer/USB to DAC (Best for audio only)

2. Direct USB (Best for hi quality video and audio combined) (most versatile for playback software, easiest to implement)

 

Which you choose is entirely up to your needs and skills. The needle is always moving, but regardless it would seem every component, power included, is a factor in SQ outcome.

 

We don't know if the Hugo 2 will require a 5Vbus input (flashing) for USB powering up. Even though the Hugo 2 won't require the 5Vbus for powering the DAC. With that in mind, I have argued with John Franks about this feature being a detriment to SQ on the Hugo's. Therefore I would recommend a clean 5Vbus be fed to the Hugo 2 if it does require this feature. I see that Mr. Watts has mentioned that the Hugo 2 will power down with 10 minutes of inactivity, regardless of input. Maybe there is hope that Chord has dropped the flashing requirement for USB implementation???

[plissken]

Why not just purchase a DAC that has properly implemented USB?

[ElviaCaprice]

Why not just purchase a DAC that has properly implemented USB?

Who said that any USB DAC has not a proper implemented USB? Wouldn't even work if not having this basic minimum. Are you just trolling for an argument? LOL

[plissken]

Who said that any USB DAC has not a proper implemented USB? Wouldn't even work if not having this basic minimum. Are you just trolling for an argument? LOL

 

No, I'm saying call up some DAC manufacturers and find out if their USB is galvonically isolated and doesn't run on buss power.

 

I know Schiit, Emotiva, Benchmark will all give you that information. Benchmark showed that their DAC was capable of pristine operation with a 100 foot cable that had a ton of noise and errors on it.

[ElviaCaprice]

No, I'm saying call up some DAC manufacturers and find out if their USB is galvonically isolated and doesn't run on buss power.

 

I know Schiit, Emotiva, Benchmark will all give you that information. Benchmark showed that their DAC was capable of pristine operation with a 100 foot cable that had a ton of noise and errors on it.

 

The op is going to use a Hugo 2 more than likely and is looking for solutions. He's not looking for another DAC. Plus galvanic isolation claims by manufacturers does not mean equality in effectiveness, including the Intona.

[mmerrill99]

Who said that any USB DAC has not a proper implemented USB? Wouldn't even work if not having this basic minimum. Are you just trolling for an argument? LOL

 

Plissken is BSing & out of his depth, as usual - he knows nothing about this even though he uses bullish statements which attempt to portray him as some sort of expert.

@miksu8 - there appear to be two factors being addressed by these USB isolators & regenerators. The first factor is leakage currents & keeping them away from sensitive areas such as any D to A conversion. The small currents are a fact of life - to paraphrase Bill Whitlock ( a wel known expert in grounding & these areas) "In UL-approved ungrounded (i.e., 2-prong ac power plug) devices (such as laptop power bricks), this current is limited to 0.75 mA. any connection between two such devices or such a device and a grounded one will carry this leakage current. We must accept this fact as reality." Isolation of the USB signal prior to the USB receiver chip is the correct place to prevent these leakage currents from affecting the internal D to A conversion.

 

Signal cleaning/regeneration seems to have a positive audible effect also but it's not exactly know what mechanism is at play here which audibly affects the D to A conversion.

 

Whether either of these will have an audible effect on your particular setup involves analysing many parameters& no definitive conclusion can usually be reached - it's a case of try & see - hopefully with devices that can be returned for refund?

[hfvienna]

The cheapest and easiest solution I would try is the Audioquest Jitterbug, which filters USB Signal AND Power to a certain extent for just a couple of bucks.. If you want to get serious I would look at home , these guys are providing professional links between source and DAC. As @mmerill99 already noted , its always a trial game here , cause every setup is special in case of grounding, noise path etc.

[miksu8]

Thank you for all the comments.

 

Regarding to getting DAC with "proper" USB implementation or galvanic isolation: Mojo and Hugo2 are portable devices so they can't draw current from the source and so can't be galvanically isolated (if I understood correctly). So getting external isolator for desktop use is the way to go and you get to use them on the go too.

 

I'm on limited budget so USB is only option. There would be some nice ethernet solutions I know

 

Jitterbug I have but for some reason I get dropouts with Mojo. Intona is getting lots of positive feedback so probably going to try it.

 

There really are lots of variables here and of course the ultimate test is to compare some devices by listening, but it's always nice to have some techical explanations too why "this should work better than that" . And getting devices for testing is not so easy here.

 

So from Ifi products I'll listen to iSilencer and micro iUSB3.0 and try to get hold of Intona too.

[miksu8]

Okay have to wait and see what is this about.

[bogi]

Signal cleaning/regeneration seems to have a positive audible effect also but it's not exactly know what mechanism is at play here which audibly affects the D to A conversion.

 

John Swenson wrote some interesting posts and articles on the topic.

About signal integrity and how it can affect DAC: http://www.computeraudiophile.com/f27-uptone-audio-sponsored/uptone-audio-regen-22803/index20.html#post418669

 

packet jitter, edge jitter, PLLs: Q&A with John Swenson. Part 2: Are Bits Just Bits? | AudioStream

 

Interconnect signal integrity handbook from samtec: http://suddendocs.samtec.com/literature/samtec_si_handbook.pdf

[Norton]

Before buying such add-ons my first question would be: are you actually dissatisfied with the sound of your DAC?

 

I ran a Hugo as a main system DAC for about 9 months via both SPDif and USB inputs from the same Bryston BDP. Yes I had a very slight preference for SPDif, but it was very slight, so i can't see that adding an isolating device to USB is likely going to add that much in the way if performance. My natural scepticism suggests to me that if this was so readily identified and important to performance, in what must be a very competitive market, it would have already been addressed by the designer. In other words, why don't Chord address this in the device itself or sell isolating devices themselves?

[plissken]

Before buying such add-ons my first question would be: are you actually dissatisfied with the sound of your DAC?

 

I ran a Hugo as a main system DAC for about 9 months via both SPDif and USB inputs from the same Bryston BDP. Yes I had a very slight preference for SPDif, but it was very slight, so i can't see that adding an isolating device to USB is likely going to add that much in the way if performance. My natural scepticism suggests to me that if this was so readily identified and important to performance, in what must be a very competitive market, it would have already been addressed by the designer. In other words, why don't Chord address this in the device itself or sell isolating devices themselves?

 

 

Good luck introducing logic to the conversation.

[mmerrill99]

John Swenson wrote some interesting posts and articles on the topic.

About signal integrity and how it can affect DAC: http://www.computeraudiophile.com/f27-uptone-audio-sponsored/uptone-audio-regen-22803/index20.html#post418669

 

packet jitter, edge jitter, PLLs: Q&A with John Swenson. Part 2: Are Bits Just Bits? | AudioStream

 

Interconnect signal integrity handbook from samtec: http://suddendocs.samtec.com/literature/samtec_si_handbook.pdf

 

Thanks bogi - I'll have a read of the Samtec pdf

Yes I read those Swenson quotes before but he also stated more recently "The purpose for both the microRendu and the REGEN is to improve the SI of the USB signal going to the DAC. Why does this make any difference? Nobody really knows. There have been several hypothesis why this may be but tracking down what is going on has been very difficult."

[mmerrill99]

Good luck introducing logic to the conversation.

The logic which makes perfect sense is that he might trial such devices himself & decide on their effectiveness.

The o/p opened this thread to ask for advice - all you offer is illogical biased & uninformed opinion.

[plissken]

The logic which makes perfect sense is that he might trial such devices himself & decide on their effectiveness.

The o/p opened this thread to ask for advice - all you offer is illogical biased & uninformed opinion.

 

It's food for thought that one might want to first contact manufacturers and get their input about how they approach their USB implementation.

 

That's the advise I'm giving.

[ElviaCaprice]

Thank you for all the comments.

 

Regarding to getting DAC with "proper" USB implementation or galvanic isolation: Mojo and Hugo2 are portable devices so they can't draw current from the source and so can't be galvanically isolated (if I understood correctly). So getting external isolator for desktop use is the way to go and you get to use them on the go too.

 

I'm on limited budget so USB is only option. There would be some nice ethernet solutions I know

 

Jitterbug I have but for some reason I get dropouts with Mojo. Intona is getting lots of positive feedback so probably going to try it.

 

There really are lots of variables here and of course the ultimate test is to compare some devices by listening, but it's always nice to have some techical explanations too why "this should work better than that" . And getting devices for testing is not so easy here.

 

So from Ifi products I'll listen to iSilencer and micro iUSB3.0 and try to get hold of Intona too.

 

 

Hold on, Alex from Uptone Audio says they have a new product coming out soon. Sounds like it will be an all in one product.

[ElviaCaprice]

Before buying such add-ons my first question would be: are you actually dissatisfied with the sound of your DAC?

 

I ran a Hugo as a main system DAC for about 9 months via both SPDif and USB inputs from the same Bryston BDP. Yes I had a very slight preference for SPDif, but it was very slight, so i can't see that adding an isolating device to USB is likely going to add that much in the way if performance. My natural scepticism suggests to me that if this was so readily identified and important to performance, in what must be a very competitive market, it would have already been addressed by the designer. In other words, why don't Chord address this in the device itself or sell isolating devices themselves?

Ahhh, because it is a portable device first! Thus it won't necessarily have access to 5Vbus for galvanic isolation. I think you're giving the DAC designers too big of shoes to fill.

[miksu8]

Before buying such add-ons my first question would be: are you actually dissatisfied with the sound of your DAC?

 

I ran a Hugo as a main system DAC for about 9 months via both SPDif and USB inputs from the same Bryston BDP. Yes I had a very slight preference for SPDif, but it was very slight, so i can't see that adding an isolating device to USB is likely going to add that much in the way if performance. My natural scepticism suggests to me that if this was so readily identified and important to performance, in what must be a very competitive market, it would have already been addressed by the designer. In other words, why don't Chord address this in the device itself or sell isolating devices themselves?

 

I have most of times been quite satisfied with my current system until heard a better system. That has happened several times Just want to make sure I have the best sound possible at my budget level.

[miksu8]

John Swenson wrote some interesting posts and articles on the topic.

About signal integrity and how it can affect DAC: http://www.computeraudiophile.com/f27-uptone-audio-sponsored/uptone-audio-regen-22803/index20.html#post418669

 

packet jitter, edge jitter, PLLs: Q&A with John Swenson. Part 2: Are Bits Just Bits? | AudioStream

 

Interconnect signal integrity handbook from samtec: http://suddendocs.samtec.com/literature/samtec_si_handbook.pdf

 

Just doesn't make sense to me how jitter or other SI errors can change sound if you have error correction at driver level. Of course if nothing gets through correctly error correcting has to give up at some point but that's not normal situation.

[Jud]

Just doesn't make sense to me how jitter or other SI errors can change sound if you have error correction at driver level. Of course if nothing gets through correctly error correcting has to give up at some point but that's not normal situation.

 

Reclocking and injecting clean power are both ways of reducing electrical noise in the DAC itself, as is galvanic isolation. This plausibly could, though so far has not been conclusively demonstrated to, reduce jitter at the DAC and/or electrical noise coming through it to the rest of the system.

 

 

Since the DAC clock itself controls timing with async USB, how could jitter be affected? Two possible ways. First, the "clock" itself is a sensitive electrical component, and noise could degrade performance (we are talking about clocks spec'd to femtoseconds). Second, the evaluation of when the signal changes from 1 to 0 or vice versa depends on a comparison of signal to a presumably silent ground. If there's noise on ground or in the signal, the timing could be affected, and thus you would have jitter.

 

 

Sent from my iPhone using Computer Audiophile

[bogi]

Just doesn't make sense to me how jitter or other SI errors can change sound if you have error correction at driver level. Of course if nothing gets through correctly error correcting has to give up at some point but that's not normal situation.

 

It's not about any difference in digital data. Its about noise and jitter, which can influence D/A conversion and this way become audible.

[miksu8]

It's not about any difference in digital data. Its about noise and jitter, which can influence D/A conversion and this way become audible.

 

 

Okay I thought jitter just adds or loses some bits which can be recovered with error correction. Is any any easy text/explanation what jitter actually causes?

 

That I understood that noise through ground wire is hard to remove inside DAC so should be done by galvanic isolation.

[bogi]

Okay I thought jitter just adds or loses some bits which can be recovered with error correction. Is any any easy text/explanation what jitter actually causes?

 

Yes, I linked an Q&A article part 2 in my previous post

http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/cleaning-universal-serial-bus-industry-standard-cables-connectors-and-communications-protocols-between-computers-and-electronic-devices-signal-digital-analogue-converter-31736/#post639093

Read also the 1st part of Q&A Q&A with John Swenson. Part 1: What is Digital? | AudioStream

 

A very simplified example scenario to make a picture (read rather the John Swenson Q&A series):

Noise originating from computer hardware (it depends on load = running software) on ground computer plane can cause time inaccuracy in generating USB packets at computer side. That so called packet jitter results to ground plane noise in DAC side USB receiver. That noise can affect DAC clock and can result to time inaccuracy of generated analog values. If that time inaccuracy has some pattern (it can depend on computer software and hardware), it can cause some form of sound coloration, detail loss or background noise. Depending on level of isolation between digital and analog part of DAC it can happen that noise from digital part can influence the analog part also directly.

[Jud]

Yes, I linked an Q&A article part 2 in my previous post

http://www.computeraudiophile.com/f6-dac-digital-analog-conversion/cleaning-universal-serial-bus-industry-standard-cables-connectors-and-communications-protocols-between-computers-and-electronic-devices-signal-digital-analogue-converter-31736/#post639093

Read also the 1st part of Q&A Q&A with John Swenson. Part 1: What is Digital? | AudioStream

 

A very simplified example scenario to make a picture (read rather the John Swenson Q&A series):

Noise originating from computer hardware (it depends on load = running software) on ground computer plane can cause time inaccuracy in generating USB packets at computer side. That so called packet jitter results to ground plane noise in DAC side USB receiver. That noise can affect DAC clock and can result to time inaccuracy of generated analog values. If that time inaccuracy has some pattern (it can depend on computer software and hardware), it can cause some form of sound coloration, detail loss or background noise. Depending on level of isolation between digital and analog part of DAC it can happen that noise from digital part can influence the analog part also directly.

 

The analog distortions resulting from jitter are -

 

- An overall increase in noise level. This is an effect of jitter uncorrelated with the signal. At the levels of jitter in current typical async USB DACs, this is often viewed as fairly innocuous.

 

- THD (total harmonic distortion) and IMD (intermodulation distortion) - These are effects of jitter correlated with the signal, where jitter on the digital side results in spurious harmonics, and those harmonics then intermodulate with the real analog signal (music). This is often viewed as a worse impact than a slight general increase in noise. However, I haven't seen citations to academic work and testing directly relating levels of THD and IMD caused by jitter with audibility, so I can't tell you what the generally accepted view is regarding the audible impact of such jitter with current typical async USB DACs, nor even whether such a generally accepted view exists.