My advice: think less from textbook theory but read, learn and experiment. Noise from computers is a real issue, especially through USB. There’s many forum posts by engineers that design DAC’s that give us a bit of an insight to what are some of the issues (like RFI noise, bad clocks, and dirty ground planes) in computer audio and DAC’s and the way they try to tackle these issues in their designs. The two below are taken out of their contexts here a bit but are IMO still interesting in a general sense.
Of course there are more ways than one to tackle these issues, one may be better at addressing an issue than another but at least these posts show the care required in a design. Workaround solutions like the many “USB optimizers” out there and also the Mutec MC-3+ USB working/having a great effect IMO shows that many great DACs are not immune or properly/sufficiently addressing the issues. At least I know that my €13k Devialet is not.
Of course there’s many more written on the net so consider these “samples”. I would recommend reading more of Rob Watts’ posts on Head-Fi, they’re excellent, honest and real-world practical. I believe he’s soon going to try a microRendu too (see the end of the thread I linked to).
The audiophile community tends to not implement the latest technology for some reason. The XMOS chips have been specifically designed to isolate the computer/USB of a DAC implementation from the digital conversion (DAC chip) side. Additionally, newer DAC chips will allow the electrical separation of the digital circuitry from the analogue:
Again, there is a lot of material there but even though it is on the marketing side, it is pretty low in fluff as these folks are selling to the designers of DACs and AV Receivers.
If you are interested in a low cost implementation of these chips, try an Aune X1s:
I have a couple and am very impressed with the sound quality. they also seem to be completely indifferent to the computer feeding the USB. I drive one from my Mac Pro and the other from a Raspberry Pi with no noticeable difference in sound quality in an informal A/B comparison using Roon and the same amp/speaker combination.
1 Like
John_Kenny
(Ciunas.biz - Digital Audio device manufacturer )
135
Absolutely agree, Antoine - the links you posted are crucial & explain where these measurements are wrong - it’s the noise floor fluctuations during music playback that is the likely issue being changed by the microRendu, NOT the static noise floor while silent or while playing a test tone.
Many people are being led astray by this whole measurements episode & what is actually being addressed by the microRendu & many USB cleaning/reconditioning/isolating devices - assuming that noise floor is the same as noise floor MODULATION - it’s not & it’s not measured in the same way
Both Rob Watts & George Klissarov (DAC designers who grapple with these issues daily in real-world implementation) recognise that noise floor MODULATION is one issue in USB audio. Noise floor MODULATION is when the noise floor changes when a dynamic music signal is being processed through the playback system. What does is mean? It means that the system’s effective resolution varies with the signal. How does this sound? Well one can read the many listening impressions of the MicrRendu or indeed go back to John Swenson’s own words:
"The microRendu produces a very clean USB signal to the DAC, which seems to produce lower noise levels in the DAC. The exact mechanism for this is not well understood at this time. The lower noise in the DAC allows the DAC circuit to operate at its peak performance. "
Note the words in bold “SEEMS to produce lower noise levels in the DAC”. Why would an engineer of Swenson’s calibre say this & then go on to say “The exact mechanism for this is not well understood at this time” if it was just static noise floor that he was talking about? Static noise floor is easy to measure & it’s certainly not a mystery or “not well understood at this time” Swenson is obviously talking about his perception of the sound which, I would expect someone to check if they were intending to do measurements of the microRendu.
So what we see in the ASR thread on the measurements of the microRendu is a wrong interpretation of the above words & the wrong thing being measured i.e. static noise floor of a DAC+microrendu while using a static 12KHz test tone.
I pointed this out on that thread & was banned !!
If you read Rob Watts you will see what he says about noise floor modulation that the Audio Precision APX55 is “Its the only test equipment I know that can properly measure noise floor modulation, as ADC’s have a lot of noise floor modulation.” The problems with measuring noise floor modulation is that you are trying to measure a very low level signal (the noise floor) in the presence of a high amplitude signals & this has to be done many times with different signal levels to see the fluctuations - accurate measurement of low level signals mixed with high amplitude signals is difficult for measuring equipment to achieve. If anyone is interested in reading further you can search Head-fi to see what else Rob Watts says about this issue.
Anyway, I thought that this was worth pointing out - the measurements of noise floor as see in ASR are misguided.
Looking at the response & measurements from AMR of the iFi iPower (in that thread on computerAudiophile) the measurements on ASR are also incorrectly done as a result of grounding issues. The measurements from AMR of the iFi iPower show that something is seriously amiss in the ASR measurements.
Thanks John and I have to give you lots of kudo’s for standing up to Amir and the funky bunch at ASR. The amount of ##### thrown at you by those flat-earthers is more than any person should endure.
Anyway, here’s another great post by Romaz/Rob Watts covering many subjects on a higher level. Of course it’s a bit Chord Dave centered but nonetheless interesting since much applies to electronics in a general sense. They also discuss the noise floor modulation issue.
[quote]
What is noise floor modulation?
What is noise floor modulation? When a sine wave signal is used in a DAC, you get different types of distortion - harmonic distortion (distortion of integer multiples from the sine wave fundamental) enharmonic distortion (distortion products that are non integer) and changes to the noise level. So for example you may have a DAC that produces noise at -120dB with -60dB sine wave (traditional dynamic range test) but the noise with a 0dB sine wave maybe -115dB - thus the noise has increased by reproducing a higher level sine wave - in this case the noise floor (seen by doing an FFT measurement) would increase by 5dB.
Now noise floor modulation is highly audible - it interferes with the brain’s processing of data from the ear - and immeasurably small levels of noise floor modulation is audible. I know this as I have listened to noise floor modulation at around -200dB - these numbers are derived from simulation - and heard the effect when the noise floor modulation mechanism was switched on and off.
What does noise floor modulation sound like?
Noise floor modulation is extremely important subjectively - you perceive the slightest amount as a brightness or hardness to the sound. When it gets bad, you hear glare or grain in the treble.
Less noise floor modulation, smoother sound quality. The curious thing about this is that the brain is very sensitive to it, so you can easily hear it. Problem is that many listeners hear the brightness as more detail resolution, and so think it sounds better - but that’s another story.[/quote]
John_Kenny
(Ciunas.biz - Digital Audio device manufacturer )
138
[Moderated]
Well, there seems to be a lot of people who have the wrong end of the stick here & elsewhere i.e. that static noise floor is what these USB devices are trying to reduce. Is it not better to correct this misapprehension than to let it multiply. It doesn’t really matter but when a device (two devices) from the same company (& I have nothing to do with that company) are hammered in the way that Amir has done with wrong measurement, then is it not better to point out how & why these measurements are wrong?
I agree that it’s much Ado about nothing but misinformation is misinformation & I guess it’s an individual’s decision how to deal with that.
I’ve moderated this thread again, after receiving complaints of inappropriate content, by deleting posts or parts of posts which are personal attacks or discussions of such attacks.
Posts discussing ideas will usually avoid moderation. Posts discussing other posters are likely to infringe guidelines, attract complaint and be moderated.
I’m stepping on comments about other posters more vigorously in this thread than may be the case on the Forum generally, because I do not want this thread to descend into pointless ad hominem accusations and replies. It lowers the standard of discussion and deters participation.
8 Likes
John_Kenny
(Ciunas.biz - Digital Audio device manufacturer )
141
The main point I wanted to make was that there are a number of audio devices that consumers can purchase which are operating in this same area of reduction of noise floor modulation (Regen, MicroRendu, Intona). These are called higher order effects by engineers & the measurement techniques to measure these effects have not yet been nailed down. However the absence of such fluctuating noise is perceptible & hence auditory perception is the best means of assessing this issue, at the moment…
Agree @John_Kenny. As I said earlier in this / other mR thread, and got flak for from a few people, your ears are the best measuring tool. I seem to be quite acute to these ground plane noises, I recognise them in playback whilst the music playing is bit perfect, it’s all there, all the detail, all the resolution, but I hear a slight graining around the edges of notes etc. To me it’s all power related, how that ‘noise’ gets through, again to me, determines how good those hardware components are in a system. What we all maybe termed as ‘digital hardness’ in the past.
Certainly, as far as using USB as the input on a Devialet 200 amp, the Regen previously and the mR now do reduce this type of noise. Beneficially, I don’t need to measure it, I can hear it, I like it, others might not. That is not expectation bias either, I did not expect either of these to make as big a difference as they have done. Indeed, when I first introduced the Regen, I was slightly taken aback, there seemed to something sucked out of the music I had been used to. Until I realised it was a layer of noise that you were attuned into before, but then it is removed (or reduced to a much lower level). This is really low level stuff, but it has an effect overall on what you hear.
I will confess that I am very happy that I am not into all the science. My mR replaced a Mac Mini and I could not be more thrilled. To my ears, it sounded incredible fresh out of the box. I let it play for 48 hours straight for burn in and have since not even considered the Mac Mini. While I have never had a Vinyl setup, my system has never sounded so good. The mR > HQP/NAA mode is phenomenal to my ears. I don’t need measurements lol
Bottom line, combination of iFi Power and microRendu are responsible for creating mains related distortion products that are not there otherwise when microRendu is tested without iFi iPower and iPower is tested without microRendu. iFi’s theory that all of this due to measurement error I am afraid does not hold water based on my testing as the measurement system remains the same in all of these scenarios.
Answering a related question, no, I don’t think these mains distortions are audible. While they are 30 db higher than what the DAC does without, they rise up to -90 db or so in low frequencies where our hearing systems is least sensitive.
Should you use it otherwise? I wouldn’t. There are a lot of choices in power supplies. If you are spending this much money, spend more and get a linear power supply to power microRendu. It is your money and I feel free to spend it for you.
Last but not least, while the iFi iPower has gotten all the attention, it is really a side show. The bigger message from my measurements which no one has disputed at theory or otherwise is that even when using linear power supplies, no fidelity improvements are seen whatsoever. The noise floor does not change. Such a noise floor was thought for sure to be lower in countless arguments until I did my testing to dispute it.
Now there are theories of dynamic noise floor but yet again no data is there to show such. The designer and manufacturer has not made any such measurements either, no is there any design implemented in there that specifically addresses this issue. It remains wishful thinking that this benefit exists.
And kudos to whoever said that if you have high fidelity USB DACs, it better darn well not be sensitive to vagaries of USB input. To think that such a DAC designer is not competent enough to accomplish this, but the designer of microRendu was using a couple of regulators and clock modules, is able to do so, stretches imagination far beyond where I want to go.
Thanks for taking the effort to do your testing and explain your results. It seems to be a thankless task judging by the responses. What I took away from your testing is that the mR, when powered by your bench PS, performed the same as the USB attached to your data source server. The iPower introduced low level, low frequency noise in the mR.
Given that we are dealing with data systems for the information being transferred to the DAC unit, the data will be unchanged. I have has a lot of conversations over the years with people who believe that changes in the data chain can affect the analogue audio, hence the proliferation of expensive USB and Ethernet cables. Yesterday I posted links to sites that directly have designed equipment and components to address USB noise, electrical isolation and the like. I find it very illuminating that no-one has taken the time to read and comment on that material. I would post some links on expectation bias and also the physical limitation of human hearing, but I don’t think anyone is interested in upsetting their belief system.
Again, thanks for taking the time and effort to test the claims of these two manufacturers.
[quote=“Amir_Majidimehr, post:146, topic:11761”]
no fidelity improvements are seen whatsoever.
[/quote] I would hope that most people would be listening for improvements in fidelity, not trying to see them.
4 Likes
John_Kenny
(Ciunas.biz - Digital Audio device manufacturer )
149
Just to clarify this, I said it before but I will repeat it again - John Swenson, the designer of this device said this
is it beyond the realms of possibility that your measurements were based on your own interpretation of what John Swenson, the designer said about the device?
There are two schools of thought, one that feel that bits of bits and everything sent to the DAC will be processed properly, and the other that the software, computer and what we are feeding the DAC can make a difference. This is fair and there will always be differing opinions. I suppose if there was a thing as a perfect DAC this conversation might not be taking place, but in my opinion there is still no such thing as a perfect DAC. I have successfully been able to listen and determine differences in software and hardware across many different operating systems, software and hardware platforms, and I am satisfied that there still are a ways to go before we reach the point (if ever) that bits are bits, and nothing else matters.YMMV.
It is not actually a matter of schools of thought. In data transmission, if there is an error the data is dropped. For audio, a person will hear clicks or drop outs depending upon the duration of the data transmission failure. A poor cable may cause these issues, but once the data is transmitted cleanly, and any decent computer store cable will do this, there is no room for improvement. As per my earlier post, if modern USB controllers (such as the XMOS) are used, there cannot be any analogue pollution coming in through the USB channel - that is the purpose of the chip. Any improvements in sound in this case based on cables or computers are wishful thinking or expectation bias.
Different DACs will sound different even if they implement the same DAC chip and USB controller because the manufacturers like to tune the analogue output stage leading to the RCA connectors (or balanced connectors). The digital domain will be identical.
