But then, since Diretta calls for two interconnected boxes instead of one, it must surely add yet another glass pane.
Three Hundred! 
It’s like Waiting For Godot, surely as dull a story as The Old Man And The Sea!
I’ll stick with empiricist - sounds better 
Measuring results are in. Please check out the new dedicated thread: Diretta Measurements and Listening Tests - Tinkering - Roon Labs Community
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Hi @Marian,
First off—Bravo.
I want to publicly thank you for the immense effort you put into building the kit, setting up the test bench, and documenting the results so thoroughly in the new thread. You promised to peel the banana, and you did exactly that.
On the Measurements
Your data is fascinating. Specifically, your findings that the power rail noise on the Target is largely indistinguishable from the Host, and that the Topping D70’s output remains identical regardless of the transport, are compelling data points.
As a tinkerer, I have to be willing to admit when a hypothesis doesn’t hold up.
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My Hypothesis: I theorized that Diretta’s steady data flow would visibly reduce voltage ripples (dI/dt noise) on the Pi’s power rails.
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Your Data: The scope traces suggest this effect is either non-existent or far below the threshold of significance on the 5V/3.3V rails of a Raspberry Pi.
This is how science works. We observe a phenomenon, we guess at the cause, and we test. It appears my specific theory about power rail noise being the smoking gun was incorrect. Thank you for testing that!
On the Listening Tests (And Why Methodology Matters)
I am glued to my seat waiting for Part 2, but I did notice a comment you made earlier that gives me pause:
“Both my sons expressed some frustration at the inability to do rapid switching… and tended to push back when I suggested they should listen for 20 minutes or so at a time.”
This is the crux of the issue.
If the goal is to spot a difference in frequency response (e.g., “is the treble brighter?”), rapid A/B switching is the correct tool. But if the goal is to detect lower cognitive load (ease, flow, lack of glare), rapid switching is the wrong tool.
Rapid switching forces the brain into a state of hyper-analytical alert. You are actively hunting for a difference. That state of high-alert focus overrides the subtle sensation of “relaxation” that Diretta brings. It is impossible to measure how relaxing a chair is if you are only sitting in it for 10 seconds while someone shouts “IS THIS ONE BETTER?!”
The fact that your kids were “frustrated” suggests they were in a high-stress analytical mode, which effectively masks the very phenomenon (listening ease) we are trying to observe.
The Remaining Mystery
We now have a fascinating paradox:
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Objective Data: Showing no measurable difference at the DAC output.
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Subjective Data: A growing cohort of listeners (myself, @Andrew_Stoneman, @Brad_Burnside, @denniswaugh, @Larry_Deniston, and scores of others) reporting distinct, repeatable improvements in soundstage and engagement.
For the pure objectivist, the conclusion is “Placebo.” That is a valid stance.
For the rest of us—the fence-sitters and the tinkerers—the mystery deepens. If it’s not power rail noise, and it’s not bit errors, what is it? Is it ground plane noise in a frequency range we aren’t looking at? Is it simply that some DACs (like your D70) are more immune than others?
Regardless, this is exactly the kind of deep-dive exploration I hoped this thread would spark. Thanks for keeping us all honest!
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Interesting comment. However, it’s only a paradox if you make it so!
I really wonder why “the fence-sitters and tinkerers” (as you said it) feel so strongly that they would like an objective, “external” explanation for the changes they are hearing. Is there some kind of loss of face to say that it could be all to do with how the brain works? Truly, I am not asking to be provocative but am genuinely interested.
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Although I have a degree in media production which included some science, such as how voice and musical instruments propagate sound, I am not a technician and happily admit to being highly suggestible. I believe that this propensity contributes to my very satisfying emotional connection with great performances realistically rendered in my own home. The goal, for me, is to be transported away from everyday existence into the music.
So I am comfortable with the mystery, however it comes out, and grateful to Marian for his considerable efforts to understand this process -with no “loss of face”. Thank you.
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Er, should these latest contributions be here - or on Marian’s measurements thread?
I’d love to know if what I’m hearing cannot be explained by measuring the gear, or that the theory of how it works is nonsense. I’m told to accept that Quantum computers rely on entanglement and tunnelling - I find the entanglement bit particular-ly (ho ho) weird
There’s a lot we don’t know…
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@Brad_Burnside and @Andrew_Stoneman - thanks for taking my comment in the spirt intended.
No problem at all, it was a fair point well put
Following on from Brad’s post above, my 40 year career has been as an industrial buyer in 20 odd different industries all around the world. Understanding how things work in layman’s terms, assessing costs, performance, weeding out marketing ■■ from genuine value etc etc is in my blood - so when I say I’m genuinely interested in how this works, I mean it
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Hi @thumb5,
I appreciate the question, and I don’t take it as provocative. It gets to the core of the philosophical divide in audio.
The Answer:
No, there is no loss of face. If tomorrow, someone proved definitively that Diretta (and all high-end digital transport engineering) is purely a psychoacoustic trick, I would happily accept that I hacked my brain for $300 and enjoy the music just the same!
Why “It’s Just the Brain” Doesn’t Fit the Data
The reason we tinkerers look for external/objective explanations isn’t ego; it’s because the “Brain/Placebo” hypothesis fails to explain two critical observations:
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Durability: Psychoacoustic bias and placebo are typically fleeting. The “new toy” excitement fades. However, the improvements reported with Diretta (and similar architectural shifts) tend to be durable. We aren’t adjusting to the sound of “no difference” over time; we are consistently finding the system more engaging months later.
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The Industry Reality: If “bits are just bits” and transport noise is irrelevant, then an entire sector of high-end audio engineering (Taiko, Grimm, dCS, MSB, Innuos, Aurender) is built on a foundation of nothing.
- These companies employ brilliant engineers who spend their careers mitigating electrical noise, jitter, and ground plane pollution.
- Are they all just selling stuffed animals or river rocks to put on speakers? Or have they identified (and solved) physical problems that standard measurements overlook?
The Middle Ground
I believe the truth lies in the middle.
- Yes, our brains are suggestible.
- But, digital audio reproduction is a fragile analog process (electricity) representing math.
It is intellectually lazy to dismiss all unmeasured phenomena as “imaginary.” It stops inquiry. I prefer to assume that if a distinct, repeatable, and durable change is heard by many experienced listeners, there is likely a physical cause waiting to be measured.
But until we find that measurement, I’m going to keep enjoying the “hack,” whether it’s in the ground plane or in my head!
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Just to be clear, I have never (and would never) dismiss a perceived experience as imaginary.
But what is your basis for making that assertion? It seems to be part of a circular argument.
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This is a great question. It stems from the first rule of signal integrity engineering: There is no such thing as a digital signal.
“Digital” (1s and 0s) is just a logical abstraction we layer on top of an analog reality.
- The Physics: To a physicist, a square wave (a perfect digital pulse) requires infinite bandwidth to exist. In the real world, we are sending analog voltage waves down a copper wire. Capacitance, inductance, and resistance turn those crisp “1s” into curvy, messy analog slopes.
- The Fragility: The receiver has to decide exactly when a “0” becomes a “1” based on a voltage threshold.
- If the Ground Plane is modulating (due to the “sawtooth” current draw of a bursting CPU), the voltage reference shifts relative to the signal.
- This causes the receiver to trigger too early or too late.
- That timing error is Jitter.
So, while the data (the math) is robust and can be error-corrected, the timing of that data is an analog property that is physically fragile and sensitive to the electrical environment.
My hypothesis is simply that by stabilizing the CPU load, Diretta minimizes that modulation of the ground reference, preserving the integrity of those analog transition points.
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HansB has done a few YTs on this subject, I believe
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But ground references are irrelevant for the transmission of digital data over USB and Ethernet. Both USB and Ethernet employ differential signalling where two lines are employed - call them data+ and data-. The data- line carries an inverted version of the data+ signal. At its simplest, when data+ is greater than data- it is interpreted as a ‘1’. When data- is greater than data+, it is interpreted as a ‘0’. The voltage levels carried on the data+ and data- lines do not matter as long as the relative voltage is correct.
The whole idea of differential signalling is that changes in signal level caused by environmental factors are common to both the data+ signal and the data- signal and thus cancel out. Simple analogue noise on the two lines does not necessarily cancel out but the difference in signal value is such that the signal to noise ratio ensures that this analogue noise is unable to affect the interpretation of the signal (except in very extreme conditions - so extreme that they will not be found in home or even office environments).
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That’s a familiar argument which might perhaps apply to a DAC receiving a data stream from something like an S/P-DIF input. You’re going to have to explain how it would apply to a DAC with a USB or Ethernet input, where the DAC necessarily has an in-memory buffer containing bit-perfect data and uses its internal clock to time conversions.
Of course, I agree that if there’s enough noise on the ground plane it will affect the analog output but that’s in the (fragile!) analog domain.
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Hi @Wade_Oram,
“ground references are irrelevant for the transmission of digital data over USB and Ethernet.”
With respect, this is incorrect.
While USB uses differential signaling (D+/D-), the USB specification explicitly requires a common ground connection between the Host and the Device. The differential receiver in the DAC measures the voltage difference relative to its local ground reference.
- If the Host’s ground is bouncing (due to processing noise), it induces common-mode noise on the D+/D- lines.
- If that common-mode noise exceeds the receiver’s CMRR (Common Mode Rejection Ratio) or the Common Mode Voltage Range, it causes timing errors (jitter) or bit errors.
Differential signaling rejects external noise (like RFI picked up by the cable), but it does not make the system immune to source noise (Ground Bounce) generated by the transmitter itself.
This is why signal integrity engineers spend their careers designing low-impedance Ground Return Paths—because the ground reference is absolutely relevant.
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Yes, there is. The fact that the physical layer works with analog voltages is not relevant once the bits are recovered and go into buffers.
Infinites are more of a mathematician’s than a physicist’s thing 
Not that it matters, as digital signaling doesn’t rely on infinites. Moreover, a square wave is but one way to transmit a digital signal. There are many other ways, many of which rely on sine carriers (e.g. phase- or amplitude-shift keying, QAM).
Again, that’s just one way to resolve bits. Other ways rely on wave fronts, so the actual shape or amplitude of the wave is largely irrelevant. And when based on threshold, the voltage bands corresponding to ones and zeroes are quite large and rarely, if ever, become ambiguous. If detection is based on wave fronts, then the shape matters even less. If digital transmissions were as fragile as you think, we would not be able to download anything from the web or use undersea cables thousands of miles long.
Which disappears without a trace once the bits are stored in a buffer and are picked up one by one by the DAC’s - not the transport’s - clock.
What happened when you unplugged the network cable with RAAT? The music continued for seconds. It seems plenty clear to me that the exact time the bits were resolved off of the physical transport is completely irrelevant.
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