Hi cumbb,
I have done that (increased power supply cap size). I have removed stupidly over-sized capacitors and restored proper values. I have un "dual mono" amplifiers off one supply (to troubleshoot when one was damaged). Imaging has never changed. Reducing capacitor size has sometimes reduced HF spikes (no shock there).
Imaging has never changed. My bench speakers are Klipsch THX6000 (not cheap), main sys to PSB STratus Gold, other system is Klipsch RP 8000. So all highly resolving systems.
I have done that (increased power supply cap size). I have removed stupidly over-sized capacitors and restored proper values. I have un "dual mono" amplifiers off one supply (to troubleshoot when one was damaged). Imaging has never changed. Reducing capacitor size has sometimes reduced HF spikes (no shock there).
Imaging has never changed. My bench speakers are Klipsch THX6000 (not cheap), main sys to PSB STratus Gold, other system is Klipsch RP 8000. So all highly resolving systems.
Hi cumbb,
I can hear differences just fine. I've had quite a lot of practice over the decades! lol!
When I hear anything, I investigate. If I see something in measurements, I listen more carefully. For sure, there are things you may hear that are tiny on a spectrum test - but they are there to be seen.
As my equipment got better over the ages, I was able to learn more. You know, show correlation between heard and measured. One thing for sure, if your equipment isn't up to snuff, you're in the dark ages where things happen by either magic or divine will. I'd much rather know the truth.
I can hear differences just fine. I've had quite a lot of practice over the decades! lol!
When I hear anything, I investigate. If I see something in measurements, I listen more carefully. For sure, there are things you may hear that are tiny on a spectrum test - but they are there to be seen.
As my equipment got better over the ages, I was able to learn more. You know, show correlation between heard and measured. One thing for sure, if your equipment isn't up to snuff, you're in the dark ages where things happen by either magic or divine will. I'd much rather know the truth.
Hi anatech,
In my modest view what you said is extremely interesting as well as extremely challenging.
Everything I'll say below is said in a humble and convinced (from my side) manner.
Also I think there is something to better define in the quoted speech.
Yours is actually a yearning that does not necessarily have an instrumental correspondent, and in fact there is nothing that measures imaging, why?
Why has no one answered this question yet?
As I've already said several times, I'm not an expert technician nor even a technician LOL, but who ever said that everything that there is to measure currently in an electrical signal corresponds to everything that we will then be able to hear at the end of the sound reproduction process that comes out of the final part of the system?
What I mean to say is that no one has ever established that an oscilloscope can show all the possible analyses of what will then be transduced from the electrical signal into an audible sound, or am I wrong?
So, as much as your yearning is laudable and certainly the more precise and expensive instrumentation will offer better guarantees of precision, but perhaps it is not only from that side that one should investigate,
But if the instrument is only an oscilloscope I do not see how one can go further,
And yet we need to go further, evidently.
Also because, for the good of Audio, and as I've already said many times (FWIW) we should unite the so-called subjectivists and objectivists not separate them even more.
To put it in a few words, if on the visualization level of instrumentations the correspondent of our eyes is the video camera, which if connected to a computer running an adequate software can do and analyze really many things, we do not have an electro-mechanical correspondent of our ears.
What about a pair of electronic/mechanical ears (of course, I'm not thinking of a "simple" stereo microphone at all) connected to a computer with proper software that were able to analyze the sound, instead of the electrical signal?
That would be a step forward in measurements and consequentially in the union of the so-called objectivists and subjectivists.
On the other hand, as I've already said many times too, an objectivist automagically transforms into a subjectivist when he listens to his newly built or just measured device.
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You can go further. Perhaps the first step would be to convey some change in imaging to another person. Certainly a YT video recorded on a cell phone isnt going to do that. I've seen expensive setups involving a head model with mic capsules embedded in the ear structure and I just didnt get it when listening to the resulting YT video. Maybe its whatever happens between the electrical signal coming off those mics and the one coming into my headphones, via YT codec - I dunno.
I did have some success with making my own recordings that way, only using capsules stuffed into my own ears, seated in front of my speakers. Playback using over the ear, open back headphones. Fairly convincing representation of what's going on in the soundfield. Proudly I say I even tricked my wife into thinking the speakers were playing, when the signal was actually only through the headphones. Other systems have successfully tricked the listener in the same way, including the far more sophisticated Siegfried Linkwitz, I once read.
If such a capture can be made with resolution enough that more than one human can hear the soundstage difference between amplifiers, then there's a chance the distinguishing recordings can be worked on by some type of analysis. I'd put my bets on AI, where it does it, but you dont get to know how it does it.
The first step is a recording methodology where I can hear it, you can hear it and she can hear it. The difference between amplifiers used, that is. Much like reproducing something in a second laboratory using the same formula. The sticky part is, if the soundstage change cant be recorded and reproduced into the perception of another person to begin with, the how else could one "trust but verify" another's claim that such happened?
Because the brain is fairly unlimited in what it can "fill in" the "I can hear it too" brings one more toward certainty that something is really happening. A colleague, deaf in one ear due to an operation, told me he still hears music in stereo! Then there's folks who dont hear spatialality at all, only tone. So it's back to I can hear it, you perhaps not, so it matters to me, you, not so much. Maybe training is effective (as I've experienced people who can hear what I cant) where the granularity of another's audio perception can be conditioned.
Just to add some food for thought,
I was watching a couple of speaker reviews on YT, along the lines of "$50k - $1zillion sound systems with dissimilar recording conditions".
Even though I was listening through ANC plastic Sony headphones, I could detect that the Cube Nenuphar 2 (FR driver with whizzers) seemed a lot more coherent and "snappy" than the Sigma MAAT (big multi-way in another video). The latter had the typical issue that multi-way systems often seem to have: comb filtering from multiple drivers spaced too far apart from each other. The image snapshot I got through headphones was that of a chorus of drivers, with various room reflections highlighting lots of interference patterns.
In another video, a bi-amped Nautilus seemed smoother, which it should, given the double-dose of band-limiting that helps reduce distortion (assuming they used active filters). It still seemed to have a little hint of a chorus effect, but the drivers seemed much more tightly integrated than with the Sigma.
~~~
Going back to the distortion aspect, say we have a left and right set of speakers playing a slightly different signal: a sine wave with a 0.5ms delay on one side and slightly different amplitude between L and R to achieve a panning effect. Added to that there's a mono sine wave playing at a different frequency.
The stereo frequency on its own would have some amount of delayed HD. Within reason, there should not be any obvious changes in the stereo effect if amplifiers are swapped and HD changes. The harmonics have the same lag as the fundamental, so the imaging and localisation effects shouldn't change.
The same can't be said about intermodulation products though. The side-band frequencies that get generated on each side have no obvious/meaningful "stereo" relationship to each other, so where do they sound like they're coming from? What's more, if a phantom image is located away from the speakers, it might be less effective at masking low level distortion that sounds like it's coming directly from the speaker.
I was watching a couple of speaker reviews on YT, along the lines of "$50k - $1zillion sound systems with dissimilar recording conditions".
Even though I was listening through ANC plastic Sony headphones, I could detect that the Cube Nenuphar 2 (FR driver with whizzers) seemed a lot more coherent and "snappy" than the Sigma MAAT (big multi-way in another video). The latter had the typical issue that multi-way systems often seem to have: comb filtering from multiple drivers spaced too far apart from each other. The image snapshot I got through headphones was that of a chorus of drivers, with various room reflections highlighting lots of interference patterns.
In another video, a bi-amped Nautilus seemed smoother, which it should, given the double-dose of band-limiting that helps reduce distortion (assuming they used active filters). It still seemed to have a little hint of a chorus effect, but the drivers seemed much more tightly integrated than with the Sigma.
~~~
Going back to the distortion aspect, say we have a left and right set of speakers playing a slightly different signal: a sine wave with a 0.5ms delay on one side and slightly different amplitude between L and R to achieve a panning effect. Added to that there's a mono sine wave playing at a different frequency.
The stereo frequency on its own would have some amount of delayed HD. Within reason, there should not be any obvious changes in the stereo effect if amplifiers are swapped and HD changes. The harmonics have the same lag as the fundamental, so the imaging and localisation effects shouldn't change.
The same can't be said about intermodulation products though. The side-band frequencies that get generated on each side have no obvious/meaningful "stereo" relationship to each other, so where do they sound like they're coming from? What's more, if a phantom image is located away from the speakers, it might be less effective at masking low level distortion that sounds like it's coming directly from the speaker.
@jjasniew
Extremely interesting and very well described indeed. 👍
Just like in other fields, where a machine (hardware+software+even AI, maybe) outclasses the human being's ability to discriminate "something".
In that case, once the appropriate standards were established, and the machine measured certain imaging characteristics of a device then if someone couldn't hear those characteristics then it would be only their "fault".
But we would know a significant piece of information, and that is that the device has an imaging of a certain type, classified according to the standards mentioned above.
In principle.
Extremely interesting and very well described indeed. 👍
A machine could do it, this is the direction my hypothetical and desirable point would go.
Just like in other fields, where a machine (hardware+software+even AI, maybe) outclasses the human being's ability to discriminate "something".
In that case, once the appropriate standards were established, and the machine measured certain imaging characteristics of a device then if someone couldn't hear those characteristics then it would be only their "fault".
But we would know a significant piece of information, and that is that the device has an imaging of a certain type, classified according to the standards mentioned above.
In principle.
The main thing is that if person believe to know all the physics in this question, then it will be ignore any real changes. Some people may not hear like another. It is normal. Hearing is a feeling and may be vary from person to person.
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Hi Logon,
You have to know the limitations of the instruments you have, and the appropriate instrument to use.
I have several oscilloscopes, one >$25K digital one. But for all the money it cost, it is a fairly crude instrument. The analogue oscilloscopes have far better resolution vertically for example, but even they are very crude. You won't get the detailed answers you need from those. They have fantastic abilities to see some things, and to store waveforms.
What you need is a sensitive spectrum analyzer with a low noise floor, and also the skill to use it. Very low noise examples are called "audio analyzers" and are very expensive. They generally cover the range up to 90 ~ 96 KHz. Their noise floors are far lower than a human being is as well. More importantly, they have something no human being has. References. They are always in calibration, consistently reading to the same standards day after day, minute by minute no matter how you are feeling. They also store, with precise readings, your measurements for posterity. That is also something human beings are horrible at.
What a spectrum analyser is normally set up to do is display signal amplitude (signal strength) on a log scale (like your hearing) against frequency, again on a log scale. This allows us to see a huge range of signal strength. Otherwise a test signal would either clip to see the other signals we don't want, or make the scale so we couldn't see them. This allows us to see what else is in there as far as signals we didn't send to the unit under test. So harmonics and intermodulation products. Our timing is far finer than humans can discern, so that is out of the question. The only two things any signal amplifier can do is add harmonic or intermodulation distortion. Compression shows up as these also.
What you hear arrives at your ears as air pressure variations. We can measure and record those. If we reproduce the same thing, the sound is exactly the same. However, once those pressure variations enter your ears, differences in tension on your eardrum can change things. So can how your mind processes those impulses, plus any idea you may have. This is where reviewers get messed up. This is where advertisers generate the results they want. This is how the audio industry (much of it anyway) makes money today. That and producing art that happens to make noise.
The current arguments stem from earlier in time when we were not able to measure things as we can today. Back in the 1970's, you were correct to say you can hear things we can't measure. You were also subject to what was in your head, mass confusion was the rule of those times. Today we can measure and that is the enemy of the advertiser or anyone with a lower performing product. Back in the early 80's, some equipment performed better and measurements were beginning to show why. Sales people had no defence but to throw confusion into the mix. However measuring and understanding grew to a point where we could see and explain.
I have been in the industry since the mid 1970's and lived through all the stupidity and lying. I am sick to death of people making a living from the surrounding confusion. They prey on folks with an open mind and lower technical ability. Many of these people do understand how things really work, yet proclaim their magic and skill makes their products better. The measuring is a science. Interpreting what we measure is a skill. Building equipment that "perfect" from our perspective is possible and has been done. That is also a skill, and it can be learned.
The age of "magic" is over. Applying skill, there is where the tricks are. Clear the air. Separate what goes on in someone's head from the actual sound pressure variations and everything becomes clear. Since we can't control what goes on in someone's head, ignore it. You can't even fully control what you are thinking. To try is to run in circles forever, but at least you'll be in good shape! lol!
The one and only thing electronics manufacturers can control is the ability to send a signal out without any added distortion. We do that and the rest is your problem.
You have to know the limitations of the instruments you have, and the appropriate instrument to use.
I have several oscilloscopes, one >$25K digital one. But for all the money it cost, it is a fairly crude instrument. The analogue oscilloscopes have far better resolution vertically for example, but even they are very crude. You won't get the detailed answers you need from those. They have fantastic abilities to see some things, and to store waveforms.
What you need is a sensitive spectrum analyzer with a low noise floor, and also the skill to use it. Very low noise examples are called "audio analyzers" and are very expensive. They generally cover the range up to 90 ~ 96 KHz. Their noise floors are far lower than a human being is as well. More importantly, they have something no human being has. References. They are always in calibration, consistently reading to the same standards day after day, minute by minute no matter how you are feeling. They also store, with precise readings, your measurements for posterity. That is also something human beings are horrible at.
What a spectrum analyser is normally set up to do is display signal amplitude (signal strength) on a log scale (like your hearing) against frequency, again on a log scale. This allows us to see a huge range of signal strength. Otherwise a test signal would either clip to see the other signals we don't want, or make the scale so we couldn't see them. This allows us to see what else is in there as far as signals we didn't send to the unit under test. So harmonics and intermodulation products. Our timing is far finer than humans can discern, so that is out of the question. The only two things any signal amplifier can do is add harmonic or intermodulation distortion. Compression shows up as these also.
What you hear arrives at your ears as air pressure variations. We can measure and record those. If we reproduce the same thing, the sound is exactly the same. However, once those pressure variations enter your ears, differences in tension on your eardrum can change things. So can how your mind processes those impulses, plus any idea you may have. This is where reviewers get messed up. This is where advertisers generate the results they want. This is how the audio industry (much of it anyway) makes money today. That and producing art that happens to make noise.
The current arguments stem from earlier in time when we were not able to measure things as we can today. Back in the 1970's, you were correct to say you can hear things we can't measure. You were also subject to what was in your head, mass confusion was the rule of those times. Today we can measure and that is the enemy of the advertiser or anyone with a lower performing product. Back in the early 80's, some equipment performed better and measurements were beginning to show why. Sales people had no defence but to throw confusion into the mix. However measuring and understanding grew to a point where we could see and explain.
I have been in the industry since the mid 1970's and lived through all the stupidity and lying. I am sick to death of people making a living from the surrounding confusion. They prey on folks with an open mind and lower technical ability. Many of these people do understand how things really work, yet proclaim their magic and skill makes their products better. The measuring is a science. Interpreting what we measure is a skill. Building equipment that "perfect" from our perspective is possible and has been done. That is also a skill, and it can be learned.
The age of "magic" is over. Applying skill, there is where the tricks are. Clear the air. Separate what goes on in someone's head from the actual sound pressure variations and everything becomes clear. Since we can't control what goes on in someone's head, ignore it. You can't even fully control what you are thinking. To try is to run in circles forever, but at least you'll be in good shape! lol!
The one and only thing electronics manufacturers can control is the ability to send a signal out without any added distortion. We do that and the rest is your problem.
@Logon
I would say its important for you to get a good handle on PSS versus non-PSS distortion and noise, the processes that create them, and how such things are measured. Otherwise its easy to get snowed by someone doing typical steady state measurements under the belief that's all there is. For one example, its now possible to measure correlated amplitude noise and phase noise independent of each other as they come out of a dac. Expensive test equipment is required, but apparently cost of test equipment is not a problem for some folks.
I would say its important for you to get a good handle on PSS versus non-PSS distortion and noise, the processes that create them, and how such things are measured. Otherwise its easy to get snowed by someone doing typical steady state measurements under the belief that's all there is. For one example, its now possible to measure correlated amplitude noise and phase noise independent of each other as they come out of a dac. Expensive test equipment is required, but apparently cost of test equipment is not a problem for some folks.
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Hi Mark,
A sine wave, or pair of them are not steady state signals. But, we can do tone bursts if you'd like. That's ancient testing.
All distortion, PSS and non-PSS distortion shows up in spectrum measurements. Absolutely anything you can think of. If you want to get fancy, gated samples.
Yeah, the cost of admission is stupid high. It is a problem for most of us, I do without other things. But to do a job properly, you simply must have the equipment required. No matter what you would rather do. Maybe the term you're looking for is commitment.
Now the phase noise thing is specific to going from the analogue realm to the digital one and back. Those sampling and clock rates are far higher than the audible range. I'll read the rest of that article (many thanks). One caution, don't try to apply ideas in one situation directly to another (called read across) without compensating for the different situation. Sometimes the data is valid, other times it is not. They are using RF concepts here, and the boards and layout can affect the outcome. These things absolutely do show up in spectrum displays.
A sine wave, or pair of them are not steady state signals. But, we can do tone bursts if you'd like. That's ancient testing.
All distortion, PSS and non-PSS distortion shows up in spectrum measurements. Absolutely anything you can think of. If you want to get fancy, gated samples.
Yeah, the cost of admission is stupid high. It is a problem for most of us, I do without other things. But to do a job properly, you simply must have the equipment required. No matter what you would rather do. Maybe the term you're looking for is commitment.
Now the phase noise thing is specific to going from the analogue realm to the digital one and back. Those sampling and clock rates are far higher than the audible range. I'll read the rest of that article (many thanks). One caution, don't try to apply ideas in one situation directly to another (called read across) without compensating for the different situation. Sometimes the data is valid, other times it is not. They are using RF concepts here, and the boards and layout can affect the outcome. These things absolutely do show up in spectrum displays.
There is something called fold-down. Just sayin'
There are also demodulation and related effects possible in output stages. If they don't stay at one frequency, then they look like noise on a spectrum analyzer with little energy in each bin. Doesn't mean they sound like benign noise though. Even white noise can sound like popping and frying.
There are also demodulation and related effects possible in output stages. If they don't stay at one frequency, then they look like noise on a spectrum analyzer with little energy in each bin. Doesn't mean they sound like benign noise though. Even white noise can sound like popping and frying.
Hi anatech,
First of all thank you again for your extremely informative and educational comment, as usual. 👍
Then, I would like to reiterate the fact that as I've already said countless times I do not have an electronic technical background and therefore what I say I do hypothetically for what I believe I have understood so far about audio technology and measurement technology about the audio signal.
That said, and not wanting to appear insistent, but if I didn't understand something, well I didn't understand it, what I would like to underline is exactly what I quoted from your (great) post because in my opinion it contains in itself exactly what I mean.
What I mean to say is that exactly as in the 70s no one imagined being able to discover, invent and build measuring equipment like today's, then today's equipment will not be like this forever because in the same approximately 50 years that separate the 70s from today then in 25 years the things discovered, invented and built to measure "audio" could, indeed should be even more powerful and precise and descriptive of what will happen.
I hope I have managed to explain what I want to say otherwise it would mean that I have understood absolutely nothing of what exists, but I still do not understand why certain things that are strictly connected with audio are still dark and they are not yet measurable.
I'm not talking about listening proofs, but about the building design technique.
Which is actually the OP's question.
Ultimately what I want to emphasize is that '70 instrumentation said much, but non too much, today's equipment tells us really a lot, but not everything.
Tomorrow's equipment could perhaps tell us almost everything, if not everything...
Just as an example, what your two fascinating discussions highlight to me (that technically speaking understand them a little only) is that there is still something to discover, and that something more is discovered step by step in audio.
It seems impossible that audio is the only technology so far from being completely understood, or even almost.
A TVC that is sold as having deep and truly black blacks is much easier to share and recognize: you look at it and realize that the blacks are truly black and deep, maybe you compare them with a visual reference and you are at peace.
Its not so much that things are unknown, its just that some things are harder to meaningfully measure than others. Also, there is still some controversy as to whether or not things harder to measure can be audible. A lot of that controversy is because its hard to do science to correlate audibility, or even design an experiment, if its hard to meaningfully measure some known physical effect.
I agree with you and others like you that I have repeated this several times around.
My view is that Physics is evolving, and so it is not at all excluded that there may be further physical effects to discover and then also to understand.
Hi Logon,
For sure. Technology marches on. Every technology. Maybe we will be able to "see" into the way someone thinks and learn more.
My point is very simple. Within the limits of what we actually do know, and we know those things for certain having investigated and proved countless times by various labs and researchers, ideas that are counter simply are not true. We know we have certain senses, we know approximate limits for our perception of the world around us. We also know why our senses and processing developed the way they did. Nature is extremely efficient. What we need to survive is there and works very well. Anything we don't need simply doesn't exist. All animals are the same, plants too.
So take that information and apply it here. There are things that are simply beyond the powers of our senses to resolve. We can measure far below those limits. Now, how some folks interpret that information can differ
As Mark correctly pointed out above, some audible things are very small features in a spectrum display. Then there is the entire variability of our perception and the way we interpret what we may hear from time to time, moment to moment. All kinds of ambiguity here. Basically a ton of noise in our observations. Sorting that out might be the actual challenge. Humans are not walking test instruments and too much in our minds affect what we think we may hear.
There are also plenty of things we can see in measurements that frankly, we cannot hear. But at least we are at that level.
Back to imaging. The sound is all time difference. A mental image is all mind. So you have to separate the technical from the psychological. You can't win with the psychological, and this does not negate the physical. In fact, it all starts with the physical, measurable stuff. If you get that right, it is entirely up to the observer and have fun controlling that.
For sure. Technology marches on. Every technology. Maybe we will be able to "see" into the way someone thinks and learn more.
My point is very simple. Within the limits of what we actually do know, and we know those things for certain having investigated and proved countless times by various labs and researchers, ideas that are counter simply are not true. We know we have certain senses, we know approximate limits for our perception of the world around us. We also know why our senses and processing developed the way they did. Nature is extremely efficient. What we need to survive is there and works very well. Anything we don't need simply doesn't exist. All animals are the same, plants too.
So take that information and apply it here. There are things that are simply beyond the powers of our senses to resolve. We can measure far below those limits. Now, how some folks interpret that information can differ
As Mark correctly pointed out above, some audible things are very small features in a spectrum display. Then there is the entire variability of our perception and the way we interpret what we may hear from time to time, moment to moment. All kinds of ambiguity here. Basically a ton of noise in our observations. Sorting that out might be the actual challenge. Humans are not walking test instruments and too much in our minds affect what we think we may hear.
There are also plenty of things we can see in measurements that frankly, we cannot hear. But at least we are at that level.
Back to imaging. The sound is all time difference. A mental image is all mind. So you have to separate the technical from the psychological. You can't win with the psychological, and this does not negate the physical. In fact, it all starts with the physical, measurable stuff. If you get that right, it is entirely up to the observer and have fun controlling that.
@anatech
Maybe I'm starting to see your point better.
I'll think about it and think about it some more...
Thanks.
And yet I still wonder: what drives a guitarist to buy a Gibson Les Paul if not its sound.
Or a Fender Stratocaster, if not to get "that" sound.
So, it may also be psychological, but there is a collective psychology of sound, in my view.
And in my opinion it should be encouraged, not hindered (I'm not saying by you, but by those who hinder it).
For the sake of audio.
Maybe I'm starting to see your point better.
I'll think about it and think about it some more...
Thanks.
And yet I still wonder: what drives a guitarist to buy a Gibson Les Paul if not its sound.
Or a Fender Stratocaster, if not to get "that" sound.
So, it may also be psychological, but there is a collective psychology of sound, in my view.
And in my opinion it should be encouraged, not hindered (I'm not saying by you, but by those who hinder it).
For the sake of audio.
Did you actually read the article?
Here is an excerpt from the conclusion:
"The power-detector option does not require a PN analyzer, which is a specialized and expensive instrument. The FFT analyzer can be implemented in GNU radio on the Z-Board, after adding an ADC daughterboard. Overall, this version probably fits in the budget of a radio amateur or hobbyist."
I was thinking about this setup:
The benefit of this approach is given as:
The other option requires a commercial PN analyzer. In fact, the design and implementation of such instrument is definitely not simple. The virtue of a fully-digital PN is the wide dynamic range, inherent in the CORDIC algorithm used to extract the random phase modulation from the sampled input [44].
My comment: already instruments such as professional PN analyzers are necessary to measure PN of clocks such as I use and some others use for audio. In fact, performance NDK SDA are measured on such equipment. If we want to obtain similar accuracy results from the approaches taken in this article, I would suspect that a more professional set of test equipment could be required.
The benefit of this approach is given as:
The other option requires a commercial PN analyzer. In fact, the design and implementation of such instrument is definitely not simple. The virtue of a fully-digital PN is the wide dynamic range, inherent in the CORDIC algorithm used to extract the random phase modulation from the sampled input [44].
My comment: already instruments such as professional PN analyzers are necessary to measure PN of clocks such as I use and some others use for audio. In fact, performance NDK SDA are measured on such equipment. If we want to obtain similar accuracy results from the approaches taken in this article, I would suspect that a more professional set of test equipment could be required.
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