Close in phase noise

[jkeny]

......

So your thesis is quite wrong. We can and do measure performance of DACs well beyond our hearing thresholds. And psychoacoustics helps us figure out audibility. What a person says otherwise is neither here, nor there unless they submit to controlled listening tests.

Ok, just to sum up this rambling post of yours - FFT of USB input shows a difference to the FFT of Toslink input BUT (& here's the crux of the matter) you state that nothing shown on the USB FFT is audible & JA listening impressions should be ignored.

 

[jkeny]

Plot is lost again. We are only talking about differences in clock oscillators that differ in performance at very low frequencies. Here is a graph that was put forward by Mike in the Rutger's write-up:

Notice that by the time we get to 100 Hz, the "old" no good clock source has noise level that is a whopping -140 db down. We are talking about part of the last bit in a 24-bit audio converter which is always noise anyway.

Keep posting about noise just to demonstrate that your really don't have a clue what phase noise means - just like your previous gaffs about USB audio retransmitting packets & oversampling in FFTs - the hole gets deeper & deeper

Above 200 Hz, they both have noise levels below -150 db which goes beyond what an ideal 24-bit DAC could produce (best case performance of an audio DAC is about 20 bits). So this discussion is not at all about "broadband signals." It is about narrowband but random noise. This is why it broadens the skirts of our test tones. Otherwise it would have elevated the entire noise floor.

My reel to reel deck has signal to noise ratio of just 80 db. Even if all of that clock noise was pumped into the output of the DAC, its contributions would have been 60 db less than my Reel to Reel deck. While I do hear the background noise in my R2R deck at times, no way, no how can you talk about audibility of such immensely low level noise profiles in digital systems.

You simply have no case. None based on engineering. None based on measurements (which you lack). None based on controlled listening tests.

It is all about inventing a problem, then building a supposed solution, which itself has not been verified to solve the original "problem." The hope is that by using fancy technical terminology, you lose the reader and they resort to lay assumptions and believe you. Not going to work here.

Again you're cracking me up with your irony, Amir - "fancy technical terminology" "not going to work here" - this is exactly what you are guilty of & you demonstrate it yet again just a post or two ago with your garbled talk about "If you keep dividing as Rob said, the energy keeps getting reduced further and further. Generalizing, your jitter gets reduced by the tune of 20*log(N) where N is the division factor." - nothing to do with what we are talking about but it's what you learned in your training so you damn well are going to try impress others with it, right?

And the hole gets deeper & deeper - they will enjoy your jokes & irony in Oz

 

[jkeny]

Just to give you a clue, Amir - phase noise is the cause of spectral impurity i.e the spreading of a single frequency pure tone into a wider frequency signal - no longer as pure a tone.
Got it?
Look it up or ask a question and show that you have some clue or have learned something about this!

 

[jkeny]

Forgot the punchline. You must, must show us measurements of what comes out of the DAC. No amount of stolen powerpoint graphs online is going to substitute for that. We don't listen to digital clock source. We listen to the analog waveform out of the DAC. You must show that design changes that are measureable at component level, also are measureable in the output of the DAC.

I didn't see your PUNCHLINE - missed the drum roll & cymbal crash
Eh no, I don't listen to the analogue out of the DAC, I listen to a transducer which is usually connected to an amplifier & maybe a preamplifier before that
So based on your simplistic logic you should be measuring the in-room signal as that's what we ACTUALLY listen to or headphone output.
You probably will not find any sign of changes in these measurements & you can rest assured that you need not worry about anything, right!!

 

[RogerD]

Just to give you a clue, Amir - phase noise is the cause of spectral impurity i.e the spreading of a single frequency pure tone into a wider frequency signal - no longer as pure a tone.
Got it?
Look it up or ask a question and show that you have some clue or have learned something about this!

About the best piece of info I have read here among all these many pages on Audio.

 

[amirm]

Just to give you a clue, Amir - phase noise is the cause of spectral impurity i.e the spreading of a single frequency pure tone into a wider frequency signal - no longer as pure a tone.
Got it?

Didn't tell you it was a single tone. I said that we are discussing a specific aspect of phase noise/jitter as embodied in your thread title which you keep forgetting:"Close in phase noise"

What makes phase noise "close in" is that it is a) bandlimited and b) is low in frequency. These will NOT generate wideband noise spectrum. They will create narrowband noise skirts as I showed in Linn turntable profile:

That is the area under our main tone identified as "Random Low Frequency Jiter." I even misspelled Jitter on purpose to get your attention!

The psychoacoustics of that is completely different than broadband noise. It is the narrowband aspect that subjects to strongest masking effect. Here is the explanation of that again from Dolby paper which covered both psychoacoustics and listening tests:

So don't keep confusing low-bandwidth phase noise with broadband.

Look it up or ask a question and show that you have some clue or have learned something about this!

Let's have you explain to analog audiophiles why the above low frequency random jitter is not bothersome to them even though its level is orders of magnitude higher than in digital.

 

[jkeny]

I'm not sure if this is possible, however but I'll try - this is just to further Amir's education - here's 3 different views of jitter taken at the same time on the same device, a Hiface




This was done with a A TEK 7354. €35,000 scope analyser & shows 3 different analysis plots of Time Interval Error function
The first being a trend plot which shows the jitter of each sample over time
The second shows a statistical histogram of jitter - showing a typical bell curve of pS jitter
The third shows the phase noise plot

 

[amirm]

I didn't see your PUNCHLINE - missed the drum roll & cymbal crash
Eh no, I don't listen to the analogue out of the DAC, I listen to a transducer which is usually connected to an amplifier & maybe a preamplifier before that
So based on your simplistic logic you should be measuring the in-room signal as that's what we ACTUALLY listen to or headphone output.

Good because nowhere do I see you listening to the clock oscillator output at Megahertz frequencies which is the sales pitch we are being subjected to.

You probably will not find any sign of changes in these measurements & you can rest assured that you need not worry about anything, right!!

"Probably?" So you don't know. Come back when you do.

 

[amirm]

This was done with a A TEK 7354. €35,000 scope analyser & shows 3 different analysis plots of Time Interval Error function
The first being a trend plot which shows the jitter of each sample over time
The second shows a statistical histogram of jitter - showing a typical bell curve of pS jitter
The third shows the phase noise plot

First of all, this shows nothing relevant to the discussion at hand. It is another pedantic attempt to say there is jitter. Whoopty do.

Second, you trying to impress folks with the price of that scope but once again, as with Mike, you don't understand the instruments used for design, versus evaluation of audio quality. As I have explained in ASR Forum thread, that is a big mistake. Here are the specs for that scope:

What do you see at the bottom? Yes, that expensive scope has dreadful dynamic range of less than 6 bits. Let me repeat, it only has a dynamic range of 6 bits or less!

It has wide bandwidth and that is what causes the effective bit resolution to shrink so much. For audio analysis though, we don't need 500 Mhz+ bandwidth. We just need tens of Kilohertz if that. That allows us to use audio optimized ADCs, giving us 20+ bits of dynamic range. This is the reason the whole world uses Audio Analyzers like Audio Precision instead of a scope. AP as a company was founded on this very basis.

I trust you have never used a Tek scope if you would have known all of this. As any senior electrical engineer if a scope can be used for audio analysis and they will tell you no.

Now, the scope can be used with additional software to make time domain measurements at many megahertz where an audio instrument cannot be used. Relying on scopes of time domain accuracy you can extract data as you are showing. As we agreed though we don't to the megahertz output of the clock oscillator but rather, the low bandwidth output of the DAC. So we measure there with the instrument made for that purpose. An audio analyzer with incredibly higher dynamic range than a scope.

Bottom line remains the same: using randomly found objective data to mislead.

 

[jkeny]

...

Let's have you explain to analog audiophiles why the above low frequency random jitter is not bothersome to them even though its level is orders of magnitude higher than in digital.

Again, simple IYI 1st order thinking & failure to deal with complexity - sorry but you failed your test, Amir

You are looking at a single tone & arguing this shows what we listen to, doh!!

Extrapolate to the multiple tones & harmonics seen in music & we see a far different picture with many skirts around many tones, overlapping each other. psychoacoustically this is broadband because the energy in these many overlapping skirts span across many critical bands in our cochlear filter.

Now extrapolate this to the dynamically changing series of tones in music & we have a noise floor of skirts which is modulating with the music

Now extrapolate this to two channel stereo where the signal is different in the other channel & we have a similar (but different) modulating broadband noise floor in each channel.

Oh & your FFTs that you believe show everything is particularly blind at showing fluctuating noise floor

Need any more help with this?

 

[jkeny]

Good because nowhere do I see you listening to the clock oscillator output at Megahertz frequencies which is the sales pitch we are being subjected to.

Still showing your ignorance in all of this & what phase noise means - go read some basic books on digital audio, Amir

"Probably?" So you don't know. Come back when you do.

I wouldn't say "probably" in your case, Amir - I would say "definitely" as you identified already your DAC likely masks any such improvements audible to the rest of us - that and/or your negative bias prevents your own discoveries - pity, but that seems the most likely explanation.

 

[jkeny]

First of all, this shows nothing relevant to the discussion at hand. It is another pedantic attempt to say there is jitter. Whoopty do.

Second, you trying to impress folks with the price of that scope but once again, as with Mike, you don't understand the instruments used for design, versus evaluation of audio quality. As I have explained in ASR Forum thread, that is a big mistake. ........

Bottom line remains the same: using randomly found objective data to mislead.

Bottom line is that measurements should be meaningful to illustrate and quantify the subject - anybody can use inappropriate measurements & wast everybody's time as you have done on so many occasions now so please don't try to lecture us about measurements.

 

[amirm]

About the best piece of info I have read here among all these many pages on Audio.

You could have saved trouble and read the ASR Forum thread where I not only explained that, but showed it with my own measurements: http://www.audiosciencereview.com/forum/index.php?threads/close-in-jitter.1621/page-2

So once again we see how revealing a simple, high frequency tone at high amplitude is in showing all that ails the DAC. For low frequency random jitter which triggered this thread, see the spreading of the main tone.

The simplicity of the test, i.e. a single tone, makes it easy to see all the distortion products as represented by the spikes, or changing of the noise floor. It is for this reason that J-test continues to get heavy use. It works and works simply to show incredibly small distortions including clock jitter.

 

[amirm]

Bottom line is that measurements should be meaningful to illustrate and quantify the subject - anybody can use inappropriate measurements & wast everybody's time as you have done on so many occasions now so please don't try to lecture us about measurements.

Have you ever performed and posted a measurement of your own on this forum John?

 

[jkeny]

You could have saved trouble and read the ASR Forum thread where I not only explained that, but showed it with my own measurements: http://www.audiosciencereview.com/forum/index.php?threads/close-in-jitter.1621/page-2

You & ASR must be desperate for attention - me. me, me, I said it first, sir - look at my webpage, sir!!

The difference between you & me is that you claim it is not audible & I KNOW it is from empirical testing!

Why I started this thread was to express my thoughts on possible mechanisms by which close-in phase noise is audible.

 

[amirm]

Again, simple IYI 1st order thinking & failure to deal with complexity - sorry but you failed your test, Amir

You are looking at a single tone & arguing this shows what we listen to, doh!!

Extrapolate to the multiple tones & harmonics seen in music & we see a far different picture with many skirts around many tones, overlapping each other. psychoacoustically this is broadband because the energy in these many overlapping skirts span across many critical bands in our cochlear filter.

Now extrapolate this to the dynamically changing series of tones in music & we have a noise floor of skirts which is modulating with the music

Now extrapolate this to two channel stereo where the signal is different in the other channel & we have a similar (but different) modulating broadband noise floor in each channel.

Great. Now explain why none of that is bothersome to analog lovers which have such effects at orders of magnitude higher than digital. That was the question.

 

[NorthStar]

John and Amir, you guys are two digital scientists. We can learn some great stuff from both of you; close in phase noise, digital jitter, digital hi-res audio from computers, etc. I have the greatest respect in audio forums with the audio people who participate in them. How can we advance all together in harmony?

 

[jkeny]

Have you ever performed and posted a measurement of your own on this forum John?

Oh, here we go - you are losing the argument so this tactic comes out of the Amir bag of debating - a well known & patently transparent tactic

 

[amirm]

The difference between you & me is that you claim it is not audible & I KNOW it is from empirical testing!

Ah, those wonderful ears of yours. Forgetting of course the thing in between them, the brain, which happily every day of the week and twice on sunday manufactures differences that don't audibly exist.

Do you think you have superior hearing to me and all the people who listen to analog audio?

 

[RogerD]

You could have saved trouble and read the ASR Forum thread where I not only explained that, but showed it with my own measurements: http://www.audiosciencereview.com/forum/index.php?threads/close-in-jitter.1621/page-2

JKeny explained it better than you have....In my view.

Quote Originally Posted by jkeny View Post
Just to give you a clue, Amir - phase noise is the cause of spectral impurity i.e the spreading of a single frequency pure tone into a wider frequency signal - no longer as pure a tone.
Got it?
Look it up or ask a question and show that you have some clue or have learned something about this!

About the best piece of info I have read here among all these many pages on Audio.