MDAC First Listen (Part 00101001)

[clivem2]

The point is surely that esoteric cable sales and foo regeneration is dead in the water if everyone realises that a systems that only sees 0 and 1 or on and off does not care about all the mush in the middle.

You need to read up on what John's Detox device is intended to do. Hint - most DACs do not seem to be immune to the effects of RF polluting their analogue stage.

 

[adamdea]

Adam have you read Julian Dunn's 'Jitter Theory' it is really interesting, Alan sent me the PDF, if you haven't I will email you the document.
Keith.

Thanks Keith, is it the one from Measurement Techniques for Digital audio ie the long article (possibly a book chapter) which you can download from Audio precision?
He was a very good writer. Great shame he isn't still around

 

[moosemeat]

John is working on it it and it is called the Detox

Yes, but that's just treating the symptoms. What ti33er is proposing would treat the cause, which presumably would be a fundamentally simpler and better solution than spawning a new industry of ReGen / Detox gadgets.

 

[Ciunas Audio]

... From the point of view of how hard the receiver has to try to read the signal (mechanism 2), it still seems to me that the pre-regen signal might be "good enough".

Apologies for the rambling, I'm just trying to work out what this all means.

But you have to pose the question to yourself "good enough" for what? Good enough for the bits to get to their destination - yes, nobody ever suggested otherwise. "Good enough" that there is no primary & secondary noise effects which have an influence on the receiving USB audio device - that is the question to pose & the one JohnW has already hinted at.

Should receiving USB audio device be immune to such noise & interference on their transmission line - yes but it's not currently possible when using USB high speed transmission to isolate the device from this noise.

A large part of the reason for this situation is that computer hardware is designed to be "good enough" to get the bits to their destination - nothing else matters. And what has been said all along is that this "good enough" is not "good enough" when analogue D/A conversions come into the picture.

 

[sbgk]

who's going to be the first objectivist to come out and say they can hear a difference now that they've seen the measurements ?

 

[Rune]

Yes, but that's just treating the symptoms. What ti33er is proposing would treat the cause, which presumably would be a fundamentally simpler and better solution than spawning a new industry of ReGen / Detox gadgets.

To me it sounds like a pipe dream that computers will come with a "true TxRx fibre optical connection port for audio equipment" without it costing ££££.

Lets be practical and get a solution for something that exist today and the foreseeable future.
I much prefer a generic solution like the Detox that can be used with any computer and DAC with USB that exists today.

 

[BE718]

But you have to pose the question to yourself "good enough" for what? Good enough for the bits to get to their destination - yes, nobody ever suggested otherwise. "Good enough" that there is no primary & secondary noise effects which have an influence on the receiving USB audio device - that is the question to pose & the one JohnW has already hinted at.

Should receiving USB audio device be immune to such noise & interference on their transmission line - yes but it's not currently possible when using USB high speed transmission to isolate the device from this noise.

A large part of the reason for this situation is that computer hardware is designed to be "good enough" to get the bits to their destination - nothing else matters. And what has been said all along is that this "good enough" is not "good enough" when analogue D/A conversions come into the picture.

The usb audio device should certainly be designed to minimise the issues even if it is not possible to eliminate them. The reason being is that "noise" in various forms from a PC is a given. Fixing the PC is not going to happen.

The other question regarding "good enough" is an interesting one, however I'm not sure we have established that this is a significant issue, let alone establish a method for measuring and quantifying the effect on the audio output.

As you know my experience has been that only a very small effect is noticed, could be I have a well behaved PC of course

 

[Rjpcardoso]

With all respect, are we not distracting from mdac2 and vfets now with the regens?
We are less than 4 months away from the supposed final products. This is something that surely we can look afterwards or will it impact mdac2 design?

Was the analogue board already tested? When will it be first auditioned? What are the next milestones for both analogue and digital boards?

Just concerned that John is taking too much on and that it may impact dates again.
Looking forward for the day when mdac and vfets arrive at my door.

 

[adamdea]

who's going to be the first objectivist to come out and say they can hear a difference now that they've seen the measurements ?

they will have to be a stupid one, because the intelligent ones know they nothing has been shown at all.

 

[JohnW]

John -thanks this is very interesting.
I'm not 100% sure what I'm looking at, could you help me to understand- is this in effect the plot of many many cycles of usb signal (voltage against time) overlaid ?

The process is called colour Grading - so from Black (no Waveform hits) to Red most Waveform "hit" areas.

If the signal was perfect with no modulation then each waveform would overlay the previous and next waveforms and displayed as purely Red with no fluctuation from one cycle to the next (no other traces or colour) - the background would be Black.

"A digital phosphor oscilloscope (DPO) uses color information to convey information about a signal. It may, for example, display infrequent signal data in blue to make it stand out."

If it is then I can see that the main signal (high crossing to low and back again forming an x) is much sharper in the second case, showing much less fluctuation from one cycle to the next.

Also I see the difference in the background colour which I understand forms some sort of spuria. I also see that there are 3 green horizontal lines on the non-regen version - what are these (are they the rest state of the signal between data?)

The scope timebase was 200pS a Div, so very fast any LF modulation causes the location of the eye pattern to shift in time - so the location of the crossing points fell into other areas which results these hits being colour graded - Lower Frequency events in Blue, more frequent events in light blue etc.

The Green graded hits indicate "medium frequency events" - so these "odd states" happen frequently - Observing the Waveforms on a very fast Analogue scope "WITH IMAGE INTENSIFIER" to allow LF events to be visible on the CRT at such fast sweep speeds (500pS Div) you can see the "runt" events directly related to the processing tasks of the PC - the frequency of their occurrence is visibly modulated by the operating system workload / operation.

I'm trying to understand how we should interpret this information. I suppose it's difficult to be too prescriptive here because it's not clear what the transmission mechanism is for whatever undesirable results we are trying to eliminate

For sure any signal with unwanted modulation is not a good thing to have "flying around" a DAC PCB - these modulation effects will be very visible with an RF spectrum analyser looking at the Audio outputs - how the Audio system copes with this is anyone guess, and this is not the only mechanism this unwanted modulation can cross into the Analogue domain.

1) the signal shape itself on the basis that it somehow directly affects the dac however it is read (as in your example of the jitter on the signal which somehow radiates within the dac even when the data is fed into a buffer via (in my words not yours) the glitch caused each time data is read into a buffer)

With any signal you need a return current path, as there is no such thing as true zero ohms ESPECIALLY at high frequency (Think GHz here with HS USB) the signal currents can be found almost everywhere on the PCB and internal to the silicon. So now you have unknown isolation attenuation between the Digital and analogue domain with such a signal, then its for sure a good thing to reduce any unwanted modulation of this signal.

2) the signal shape insofar as it causes the usb receiver to have to try hard to read the data (this is what I understand to be JS' hypothesis)

No, I totally don't agree with JS's hypothesis, I think John misses the main point about the unwanted modulation encoded within the USB signal - as the Colour graded plots clearly show.

3 the noise in the signal (not the 5v line) which somehow pollutes the dac through some other mechanism
[have I got this right- are there other mechanisms I have missed]

Yes, unrelated RF noise on the Data lines also needs to be attenuated which requires RF filtering - a separate function to the data repackaging / timing.

4) the noise on the 5v line (not not relevant to this plot I assume)

Not directly related, but any noise on the 5V line (and thus Ground) will couple into the Data lines, so should be avoided.

Having regard to those considerations (particularly the first and second). I'm trying to get my mind round the question of what it is about the signal that really matters. Am I right in thinking that because usb is a differential signal the receiver would automatically ignore the common mode noise, as it would be reading the difference signal?

What do you think the Common Mode rejection performance will be at 1GHz? even my US$5K Tek test probe is only around 20dB CMR at 1 GHz, I can assure you that the USB Cable / interface will be less then this!

Apologies for the rambling, I'm just trying to work out what this all means.

Yes, I seem to have awoken some deep seated concerns - but atleast I have been able to measure quite a significant modulation of the USB Data related to the CPU / System processing which opens the possibility that the "Bodge fix" attempts of optimised software players might have a foundation in "reality" - although they are a very wrong / incomplete band aid to a problem that should not be allowed to cross into or even effect the analogue domain in the first instance.

 

[Ciunas Audio]

The usb audio device should certainly be designed to minimise the issues even if it is not possible to eliminate them. The reason being is that "noise" in various forms from a PC is a given. Fixing the PC is not going to happen.

First, an understanding of the cause & effect is needed before any definitive statements are made. Noise is such a general term & this needs to be analysed & defined to identify the characteristics of the noise & maybe correlate to the effect on SQ. At that stage we should be in a better position to say what can & can't be done at the PC end, the transmission stage or at the receiving USB device.

The other question regarding "good enough" is an interesting one, however I'm not sure we have established that this is a significant issue, let alone establish a method for measuring and quantifying the effect on the audio output.

As you know my experience has been that only a very small effect is noticed, could be I have a well behaved PC of course

As I said to you before there could be something masking this effect from you or indeed you could have a Sony laptop which is blameless as far as noise is concerned - a very unlikely situation, don't you agree? You stated before that this was your Regen test config & not a PC, right? "MDAC and Oppo PM1 fed from Sony laptop running Win 10 and Roon or Jriver".

 

[JohnW]

With all respect, are we not distracting from mdac2 and vfets now with the regens?
We are less than 4 months away from the supposed final products. This is something that surely we can look afterwards or will it impact mdac2 design?

Was the analogue board already tested? When will it be first auditioned? What are the next milestones for both analogue and digital boards?

Just concerned that John is taking too much on and that it may impact dates again.
Looking forward for the day when mdac and vfets arrive at my door.

Today I'm back working on the MDAC2 analogue board - The Detox project is an evening project to help keep the mid fresh.

The target is to release the updated analogue PCB design for T0 (production line built sample) in October, and within the week I hope to have the Quote for the FDAC / VFET amp chassis so we can proceed with to sample units.

The indepth investigations into the USB is not confined to the Detox only as I'm sure there will be a direct benefit to the design of the FDAC Digital PCB (its USB interface).

 

[JohnW]

they will have to be a stupid one, because the intelligent ones know they nothing has been shown at all.

I don't agree, I have shown that the USB data stream is heavily modulated by the processing actions of the Host PC - and that a USB Hub device repackages and re-times these USB data packets I believe that this is the first time its been shown in an Audio related thread, although technically it will come as no surprise as its very simple to understand the mechanises involved - and to be expected.

The argument that will rage is how does this modulation mechanism cross into the Analogue domain (with a well designed product it should not)... but I've heard its effects in many instances so its not so important to me ATM... I know what can to be done to attenuate the unwanted signal modulation - that's what I'll work on.

I do know that when a person has a deep seated belief no 'snip-its' of information that might bring into question this belief will cause them to question their opinion...

My concern is to resolve issues that I believe can effect the audio domain - while I can measure a host of undesirable signal modulations, at the end of the day my results are judged by listening - and then each to there own

 

[Ciunas Audio]

I don't agree, I have shown that the USB data stream is heavily modulated by the processing actions of the Host PC - and that a USB Hub device repackages and re-times these USB data packets I believe that this is the first time its been shown in an Audio related thread, although technically it will come as no surprise as its very simple to understand the mechanises involved - and to be expected.

The argument that will rage is how does this modulation mechanism cross into the Analogue domain (with a well designed product it should not)... but I've heard its effects in many instances so its not so important to me ATM... I know what can to be done to attenuate the unwanted signal modulation - that's what I'll work on.

I do know that when a person has a deep seated belief no 'snip-its' of information that might bring into question this belief will cause them to question their opinion...

My concern is to resolve issues that I believe can effect the audio domain - while I can measure a host of undesirable signal modulations, at the end of the day my results are judged by listening - and then each to there own

Isn't that the truth!!
I believe it goes back to how the mind works - we have two mechanisms that are at play - the part that doesn't use rationality but comes to quick conclusions based on other factors & the part that uses rationality. By & large we make most of our decisions with the first mechanism & rationalise the decision with the second. Science & objectivity is meant to use the second mechanism.........

I started a thread on here last year which proved to be very interesting called "Sorting out evidence-based from faith-based"

 

[iansr]

Isn't that the truth!!
I believe it goes back to how the mind works - we have two mechanisms that are at play - the part that doesn't use rationality but comes to quick conclusions based on other factors & the part that uses rationality. By & large we make most of our decisions with the first mechanism & rationalise the decision with the second. Science & objectivity is meant to use the second mechanism.........

I started a thread on here last year which proved to be very interesting called "Sorting out evidence-based from faith-based"

Yup there is a whole new science developing about how we make decisions. There was an Horizon programme about it a little while back. We are a lot less rational than we think we. I've always believed the instinctive part of our psyche has a much bigger influence on our behavior than we give it credit for, and this is one manifestation of it. Are you sitting in my chair?

 

[JohnW]

Done some listening evaluation of Regen and AQ Jitterbug in my system this weekend.

Using Roon (go try it if you haven't already) as player, overspecified MediaPC w. PPA v2 USB card (HDPlex LPS) - AQ JB - Regen (HDPlex LPS) - Norma Internal DAC.

Listening on my goto evaluation CD-rip "The All Star Percussion Ensemble". Improvement noticed when I added Regen in my system, no improvement noticed when adding the AQ JB.

I'd agree that the Regen resulted in the greatest measurable difference to the downstream USB Data

 

[clivem2]

Could it be that some objectivists form a (subjective) view then search for data to support this? Surely not....

 

[Sibbers]

The target is to release the updated analogue PCB design for T0 (production line built sample) in October, and within the week I hope to have the Quote for the FDAC / VFET amp chassis so we can proceed with to sample units.

The indepth investigations into the USB is not confined to the Detox only as I'm sure there will be a direct benefit to the design of the FDAC Digital PCB (its USB interface).

Amazing, I was just about to ask about this. Sadly I don't know enough about the USB regen and filtering biz to take part in the conversation and am really just waiting for a conclusion... It seems like it works, and if the isolation principle is applied to the FDAC then I feel like I've just aquired another unknown benefit.

The SQ is the obvious primary reason to be excited, but actually I'm still really excited about the EQ in the digital domain. Do you think there is a chance we can adjust levels (as many as you can fit) using the buttons on the case and the screen as an indicator?

Also for DRC, is each speaker treated to its own set of filters? Aaaaaaand, can we save profiles for those who like to move their speakers around?

Do you think realistically there is a chance to have this all done before xmas? it just seems like it's hurtling towards us...

 

[JohnW]

John,

Even though I don't really understand what I'm looking at, the difference is so spectacular that I have to wonder if you have quietly taken a job as a sales rep for Uptone Audio!

It is very clear from these that what is going to the DAC is drastically different in the two cases. I know it's a long stretch from the pictures to be able to say that this is a difference which we can hear, but at least it correlates well (even to the 'blackness' which some people report for the sound with Regen....). You don't say anything about PS, so I assume this is with the SMPS, and I'm quite anxious to see what comes from using a linear supply. Nevertheless this is a clear demonstration, probably the first one, that the Regen really does do something measurable to the data.

Hey just saying it as it is

I've was sent the Regen and Jitter Bug by a fellow PFM member but without PSU, so these test where performed with a low noise linear lab PSU.

Without doubt, the normally supplied SMPS will be worst - if I get my hands on a unit then I can post the measurements...

 

[Ciunas Audio]

Could it be that some objectivists form a (subjective) view then search for data to support this? Surely not....

Wash your mouth out & perish the thought!!
But it's no different from how we all come to decisions except a lot of us don't bang on incessantly about "proof" which makes it just so much harder to take.