Why different roon bridge sounds different

(Mr Fix It ) #41

[rant]You will never ever hear the same sound twice. Think about it…the slightest changes in anything like the position of your head in the listening space, the air pressure and temperature, the placement of your shoulders or glasses or breathing in and out or the blood rushing in your head or the expression on your face. Forget about 2 people hearing the same thing…even if the sound source is 100% repeatable, you will not hear it identically ever again.

Shoot me down…nobody hears the same thing…everyone hears differently. Who taught you to hear? When do you remember starting to hear? How do you know you are doing it correctly?

It all comes down to if a difference is sounding better or worse to your ears…who else do you have to please…unless you are producing a track for others consumption…in which case you have no control over anything despite how you think it should sound.[//rant]

(Fernando Pereira) #42

Chapter 4 surveys several subtleties of human hearing and measurement techniques like correlograms that get a bit closer to those subtleties. I only sort-of understand a fraction of what is there, but I’ve also had many conversations over the years about the limitations of standard measurements with pros. The practical comparisons between different digital source methods that I’m most confident of involved listeners who did not know which source was playing; they reported on (small-ish) differences consistently. On the other hand, I totally agree there’s a lot of magical thinking (cables, don’t talk to me about cables!) in this field.

(Derek Wyman) #43

Another thing to keep in mind is how our ears (our brains, really) get “used to” and then adjust to what we hear. A lot of “burn in” rhetoric is more about our brains getting used to a different sound then it was used to.

I just swapped speakers after about 20 years and had to keep telling myself just to wait for a bit until everything calmed down. My brain knew exactly what every track was supposed to sound like. And it would be easy for me to try to chase that sound instead of trying to make a decision on what sounds “better” to me. Not objectively more accurate, but more pleasing to me. I’m a big proponent of transparency in equipment but not naive enough to think that i don’t like a little less-than-perfect reproduction in real life.

(Reader of the Internets) #44

I’m completely on-board with respect to the mysterious and unpredictable vicissitudes of human hearing, including all the psycho-acoustic effects, including expectation bias. But the OP was wondering how two different streamers, which convey the same bits in the same way to the same DAC and the same downstream analog configuration – same amps, speakers – could sound different.

@wizardofoz suggests nothing ever sounds the same, and that could be true, but I don’t see how it advances the question. The OP suggested the effect was repeatable.

I think the only possible “mechanical” (that is, non-psycho-acoustic) hypothesis (aside from some Gaslight scenario with aliens playing the part of Charles Boyer using powerful electromagnets to differentially affect Isiah’s brain to mess with his hearing) is electrical or electromagnetic coupling between the streamer and the analog equipment which induces distortion, either in the operation of the DAC itself, or in some latter part of the analog chain. Could be through the power supply connection to mains power, the USB cable, or through the air due to some unfortunate routing of susceptible cables serving as antennas.

Archimago’s tests, which seem to me adequate for his purpose, reported only that he couldn’t find such distortion in his streamer+DAC setup. Clearly his setup is not going to be the same as any of ours, if only because of the routing of cables, so any extrapolation of his results to our equipment have to be made judiciously.

(Frank Daman) #45

The DAC is the same. I don’t know the DAC, but it seems to be a plug-in card. It follows that it will be running on different hardware with different drivers and from a different motherboard in each case. Just the drivers themselves could cause a difference in signal.

Hoofbeats, zebras, horses,…

(Michael Fanning) #46

@Bill_Janssen You’ve hit the nail on the head. As my favorite just-departed screenwriter William Goldman famously said, “Nobody knows anything… Not one person in the entire motion picture field knows for a certainty what’s going to work. Every time out it’s a guess and, if you’re lucky, an educated one.” We all have different set-ups with unique networking, cabling and environmental issues. One person’s educated opinion can help us discern the truth but there’s no Deus Ex Machina to save each of us!

(Anders Vinberg) #47

Gah. Double gah.

Goldman is talking about predicting what the audience will like.
But his statement does not apply to more engineering oriented aspects of the movie industry, such as how to manage exposure of the film given cameras and lenses and lighting — they are quite expert and quite predictable. I believe a cinematographer who told the producer and director that nobody knows anything and we will just have to try a few exposures and see how it works out would soon be driving an Uber.

Audio equipment is engineering.

If you say nobody knows anything and anything can affect the sound in totally unknowable ways — why are we even having these conversations in these threads? Even recommendations by other users would be meaningless, because my house may be different than yours.

(Mr Fix It ) #48

The OP was moving a USB DAC from an iMac to Raspberry Pi…so on the digital side you have isolation via the network (Wifi) but the software side of the USB connection would be different - Alsa vs Core Audio.

I cant know if the USB is also providing the power supply for the DAC as its not mentioned that I scanned for - but that would be another significant contributor if it’s different.

Note I saw mention that the RPi is powered bu a 1A iPad charger!!! A RPi is spec’d to require a 2.5A charger just as an FYI. Adding on a USB powered DAC or HAT could very well require more than that.

(Anders Vinberg) #49

Yes, I expected this answer, it’s the standard subjectivist argument, that measurements are useless because we don’t measure the right things and don’t even know what we don’t know.

It is not entirely unreasonable. There have been times when we have discovered things we didn’t know. I remember when Matti Ottawa discovered crossover distortion, which had not previously been known and was the cause of many well-measuring amps sounding bad.

But there is a difference: Ottala was an engineering researcher, he assumed there was a technical reason for the observed misbehavior and set out to identify the cause, and identify a way to measure it. Most of today’s subjectivist affirm, proudly, that it is impossible to understand what makes a device sound good or bad because it is a process that involves the human neuro-physiological system, and the human psyche, which are unknowable.

I don’t accept this. And I don’t believe that competent engineers operate that way.

There is a common pattern where the latest problem is rolled out as an explanation for alleged effects. Feedback. Phase discrepancies. Jitter. Now it’s noise.

Jitter is certainly a real problems, but it is not a factor in asynchronous transfer. Wikipedia: jitter is the deviation from true periodicity of a presumably periodic signal. The network is not presumably periodic, it is packet switching and the foundational technology does not even guarantee that packets are delivered in order, or correctly, or at all (why the receiver can request retransmission). If I were to tell you that my CD player suffers from severe jitter because Fedex delivers the packages from Amazon only once a day and not on sundays, you would rightly consider me a fool — Fedex is not part of the “presumably periodic” delivery chain, periodicity is introduced later. But if I offer an audiophile network cable based on its low jitter, I am afforded great respect and large checks.

Noise is a real problem that plagues some systems, and there are techniques for remediating it. But it is not a mystic, spiritual thing. It is possible to measure it, and to A/B test it. And if a remediation is offered (for serious money), it is possible to determine if it does indeed do so, if it is an effective solution, both in terms of reducing the noise and in terms of reducing the putative secondary deleterious effects (where people say the noise may not be measurable or audible but can impair sound indirectly).

If the device is not proven to work, through measurement or rigorous listening tests, but people claim to hear the improvement — I don’t care what you do with your money, but we should not base our engineering on faith.

(Sean) #50

This is a little bit over the top. I’ve been on this forum approx. 3 years and I notice each year you get more entertaining on these subjects :grin:

The measurement gear being used to create the gear we love has gotten us to this fantastic point - nobody questions that…

The designer of the Hugo2 you have, Rob Watts, has his own APx555 (doesn’t belong to Chord). I’m not sure Archi’s gear is as sensitive… And if you ask the designer of that state of the art DAC you have there, he will say that his state of the art measurement gear is not as sensitive as the ear/brain system… I know he will say this, because I’ve had this discussion with him :wink:

The measurement gear being used to create the gear we love has gotten us to this fantastic point - nobody questions that…

Rob says his DACs measure at the limit of his state of the art AP machine… he’s building what he believes to be the greatest ever A-to-D converter, not only for commercial applications (Pro Audio) but to also help with better measurements for his own future designs…

Things may be more complex than Archi’s measurements can show and more complex than perhaps you (and I) may understand…

This is an interesting post and in fact the entire thread is interesting:

"I don’t think anybody is trying to invalidate Fourier Analysis. It just has lot of limitations that are good to acknowledge. Other algorithms don’t have the same limitations, but human hearing is still pretty much among the best algorithms there are. And can beat Fourier transform in decomposing frequencies on time-axis (time-frequency analysis). I think this is one of the best quotes from the researches I agree with:

We were still extremely surprised by how well our subjects did, and particularly surprised by the fact that the biggest gains appear to have been, by and large, in timing. You see, physicists tend to think hearing is spectrum. But spectrum is time-independent, and hearing is about rapid transients. We were just told, by the data, that our brains care a great deal about timing.




(Isiah Lau) #51


Thanks for bringing this up again.

The USB doesn’t provide power supply to DAC. It’s self powered and the USB power pin is not connected according the manufacturer. From the following diagram, I guess it means pin 1 and pin4 are not connected at all inside the device?

Actually, I changed to Raspberry pi stock power supply (5v 2.5A). There’s no sound quality change.

So you are right. This is a long thread now and somewhere I already mentioned. If all physical connections don’t matter, I am pinpointing the software difference: ALSA and CoreAudio.

But some people saying the bitstream of ALSA and Coreaudio to the USB DAC should be the same, is that true? This makes me recalling the software Audirvana Plus. With Direct mode (bypassing coreaudio) or through coreaudio sounds absolutely different. That means coreaudio DO change the sound, doesn’t it?

Talking about how to measure the result from @andersvinberg @Bill_Janssen @Fernando_Pereira , can we simply use this device?

(Fernando Pereira) #52

I’ve spent quite a bit of time over the years with top audio engineers who designed some of the signal coding, compression, and enhancement methods that we all use every day. They are a lot more humble about what their bench measurements get and what they don’t know how to measure than you seem to be. That’s why every major advance in audio processing also required extensive human testing.

Of course we amateurs often share impressions that are indeed subjective because they lack adequate controls. But that does not imply that bench measurements are enough to exactly predict the full details of human response in controlled conditions.

Anyway, we are obviously stuck, no different from the typical political or religious discussion.

(Mr Fix It ) #53

@Isiah_Lau1 not sure if you are one and the same as @Isiah_Lau - I shall assume you are…

if you have another Mac / Mac mini / MacBook etc. to try via a network stream to roon bridge running on it only in place of the RPi and see how that sounds perhaps

(Sean) #54

I’ve seen people claiming to know more about measurements than the actual designers of the very same gear that they love and enjoy every day… Always entertaining :grin:

(Isiah Lau) #55

I didn’t know I was using two accounts! Sorry.

Yes let me try later. In fact I tried some other idevices. iphone 6s/iphone Xs/iPad Air 2 sound almost the same. iPad Pro 2018 uses USB-C and sound a bit different.


From my own experiments powering an Odroid C2 endpoint with the Hardkernel wall wart and a very quiet LPSU there’s a palpable reduction in noise floor during playback. The USB input on the DAC I used is externally powered (pity). Using a modified USB header to enable the USB input to be independently powered (ie taking the data feed only from the Odroid) yielded no additional reduction in noise floor.

Conclusion: Electrical noise from the source device definitely made its way into the audio chain on this DAC. The weird thing is it wasn’t at all discernible until presented with a quieter input at which point the lowered noise floor was obvious.

(Mr Fix It ) #57

I was powering a khadas tone board with a rpi powered by the HDD Usb connection from a set top box…yeah I know (_8{} DOH but it was the closest Usb I had at the time and then I heard at some time later there was some horrid noise being made by my speakers…even on other inputs than the TB Dac until I moved it to a different Usb device (Nuc/rock) and all was dead quiet again…power supplies matter for sure.

(Anders Vinberg) #58

Touché :joy:

Yes, auronautical engineers are pros, but they still have test pilots.
And Rob Watts and Ted Smith and engineers like that do listening tests.

What troubles me ranges from charlatans to mysticism to misleading beginners.

(Sean) #59

And do you know what kind of listening tests they (Rob and Ted specifically) do? The answer may disappoint you and Archimago… but best you take up that discussion with them directly…

(Isiah Lau) #60

OK, to answer my own question about should coreaudio and ALSA sending the same bitperfect stream (which previously answered “yes” in this thread), I finally came across this article with further information

Archimago said this in the conclusion:

Whether in the past with Mac OS X, or Windows, and now Linux, there is no evidence that operating systems make any difference to sound quality if you’re playing “bitperfect” to the hardware directly (ie. ALSA to DAC with no software conversion similar to Windows ASIO, Kernel Streaming or WASAPI). Obviously this statement would not apply to sounds running through an internal mixer/DSP like PulseAudio or Windows mixer. Likewise, I see no evidence that we should be concerned about jitter of any audible consequence these days with asynchronous USB DACs like the Geek Out V2.