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Ooooh... Charts and Graphs

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stereotactic

Experienced
No, I'm saying that the tests in the OP don't measure aliasing, unless something has been done to completely isolate the effect of aliasing (which it plainly hasn't) from any other effects. TrueRTA is a spectrum analyser, not an aliasing analyser.

I believe the "isolating effect" is that the Axe models exclude analog thermal noise from the modeled amp. Not sure what other brands do, but I and probably most other modeling converts do not require an exact replica of all aspects of the amp such that it includes idling high gain hiss or other non musical artifacts of the analog amps. As I mentioned previously, the lack of hiss and hum in my high gain amp blocks and that very low noise floor seems a distinct advantage in my quest for clarity and detail. It's yet another way amp modeling can excede the real thing, like there being no possibility of the preamp oscillating at the highest gain settings

Is there such a thing as an "aliasing analyzer"? I could find no mention of one on the web. A spectrum analyzer is an aliasing analyzer if the only analog thing being inputted into the model and then outputted into said analyzer is a tone going through a digital architecture replicating a high gain amp signal path. As I understand the graph, the only other analog signal in evidence in the graph beyond the 9-11k tone, are the harmonics from the mains voltage. If there were other analog noises mixed into a high gain architecture, like modeled high gain hiss, I think it would be much louder than the harmonics from the mains hum and would show up as something with an amplitude higher than the mains harmonics, but less than the 9-11kz tone. The absence of any higher amplitude/gained up analog noise modeled artifacts and the low Axe noise floor leaves only aliasing, right?

You'd be quite surprised how closely an amp's response under identical conditions (the 9-11kHz sweep) matches that of the Helix...

As above, there are plenty of things about real amps I'm happy to have left out of a modeler, like tone controls that barely do anything when an amp is gained up high, the weight of my Marshall Major's transformers and cabinetry, standby switches that barely work...

"Noise curve" is Copyright Me, 2018. Just a way to describe the graphs in the OP, since they obviously don't just show aliasing (see above). If it did, then a real amp would show zero response apart from the original signal and the harmonics - would you like to place a bet on whether that's true or not?

(I wouldn't take the bet, 'cos I already know the answer and I'm cursed with a sense of ethics).

Oddly, the more accurate the modeller, the more noise you'd see - if every component in an amp is modelled perfectly, then the overall model will display just as much noise outside the original signal as the original amp did, and that wouldn't be aliasing.

Bet? I'm just tying to understand where the misunderstanding is, yours or mine. Ethics? Axe grind much? Pun intended..:)

Where did you get this zeal for "accuracy" and "perfection" in modeling? How granular is your definition of "accurate"? It would appear that it's a good deal more granular than mine.
 
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NeoSound

Fractal Fanatic
Cliff simply states the hardware in the III has superior performance to other tested units in a certain areas. What we know about the hardware specs and potential of the Axe III so far seems to be FAR beyond any other device yet produced for guitar sounds. For someone to start posting brand x that was designed several years ago with mass marketing in mind is just as good as the III has some kind of issues or agenda?
 

digitalscream

New Member
I believe the "isolating effect" is that the Axe models exclude analog thermal noise from the modeled amp. Not sure what other brands do, but I and probably most other modeling converts do not require an exact replica of all aspects of the amp such that it includes idling high gain hiss or other non musical artifacts of the analog amps. As I mentioned previously, the lack of hiss and hum in my high gain amp blocks and that very low noise floor seems a distinct advantage in my quest for clarity and detail. It's yet another way amp modeling can excede the real thing, like there being no possibility of the preamp oscillating at the highest gain settings

Yes! Now we're getting somewhere. The issue here is that while the Axe models may exclude analogue thermal noise, the assumption in Cliff's post is that the Helix does too. Personally, I'm absolutely cool with the flaws of the original amp's topology being represented in the modelling...I can understand why other folk might not be, but the assumption that it must be aliasing isn't supported by the data presented because - as I've said repeatedly - there is no "control" plot, which would be an amp of the original model. It wouldn't be perfect, because it wouldn't have been the specific amp being modelled (we all know that 1950s tech can be variable at best...just ask Nuno about the amp he used on Waiting for the Punchline...), but it would give a big pointer to that.

Is there such a thing as an "aliasing analyzer"? I could find no mention of one on the web. A spectrum analyzer is an aliasing analyzer if the only analog thing being inputted into the model and then outputted into said analyzer is a tone going through a digital architecture replicating a high gain amp signal path. As I understand the graph, the only other analog signal in evidence in the graph beyond the 9-11k tone, are the harmonics from the mains voltage. If there were other analog noises mixed into a high gain architecture, like modeled high gain hiss, I think it would be much louder than the harmonics from the mains hum and would show up as something with an amplitude higher than the mains harmonics, but less than the 9-11kz tone. The absence of any higher amplitude/gained up analog noise modeled artifacts and the low Axe noise floor leaves only aliasing, right?

No, to my knowledge, there is no such thing as an aliasing analyser - that was kind of my point. Apologies if I didn't make that clearer :)

As above - if you assume that the Axe noise floor is that low (I haven't seen evidence, but I can well believe it) and you assume that the Axe's modelling deliberately discards bits of the original amp's signal that aren't deemed desirable (like the thermal noise, poor signal path isolation etc), then yes...that works for the Fractal gear. I'm not so sure about your other suppositions, though; whenever I've encountered ground loops the hum has been much more apparent than any hiss introduced from multiple gain stages at high signal volume. However, we don't really have a frame of reference here, which is why I was asking for more details on the test setup so it could be replicated.

As above, there are plenty of things about real amps I'm happy to have left out of a modeler, like tone controls that barely do anything when an amp is gained up high, the weight of my Marshall Major's transformers and cabinetry, standby switches that barely work...

Definitely with you on the weight thing; my whole rig weighs about 25kg 'cos I'm a broken shell of a human being and any more would mean I'm sitting in a wheelchair on stage every night ;)

As for the rest of it...that's down to taste. I'm firmly of the opinion that a lot of amps - particularly older ones - sound the way they do because of the flaws and stuff that are mild annoyances, but add to the subtle differences in behaviour.

Bet? I'm just tying to understand where the misunderstanding is, yours or mine. Ethics? Axe grind much? Pun intended..:)

I'd like to know more about it, so I can try to run these tests myself and work out what's aliasing and what's deliberate. I don't think anyone's misunderstanding stuff, really, because there isn't enough information presented to get to any conclusion at all.

Where did you get this zeal for "accuracy" and "perfection" in modeling? How granular is your definition of "accurate"? It would appear that it's a good deal more granular than mine.

For my part, I think I've already explained that up there ^^. I don't have a zeal for it, I'm just aware that it presents an explanation for the noise across the spectrum which is a plausible alternative to Cliff's assumption that it must be aliasing and therefore poor design.

Cliff simply states the hardware in the III has superior performance to other tested units in a certain areas. What we know about the hardware specs and potential of the Axe III so far seems to be FAR beyond any other device yet produced for guitar sounds. For someone to start posting brand x that was designed several years ago with mass marketing in mind is just as good as the III has some kind of issues or agenda?

As my history teachers always used to tell me..."Consider the source". Cliff has a very obvious vested interest here, so - from somebody who really have an axe (heh) to grind either way* - it pays to be somewhat skeptical when presented with contextless information that doesn't seem to stack up with real-world experience. I'm more than happy to be proven wrong, but I want it to be proven for the sake of improving my own knowledge.

However, I think a healthy skepticism is always a good thing.

* Yes, I own a Helix LT, purely because I can't afford an AxeFX to be able to compare it to at the moment, and a rack unit wouldn't suit my current needs. If there's something better out there for my needs, though, I want to know about it - and that's what this is about, wanting to know more. The Helix is my first Line 6 product since the POD 2.0, so I'm by no means wedded to the brand...in truth, my audio needs amount to "Does it do a really good impersonation of a SLO?", which is probably significantly less onerous than what you guys do with it.

Maybe because the interface they used to record the amp introduces aliasing too?

Also an excellent question, and something to be borne in mind. In fact, while we're at it, why not ask the question of the one that kicked all this off - why, when measuring aliasing, was an analogue signal path involved at all (at least with the Fractal units, given the ground loop) when the modelling could've been directly tested via USB without passing through the converters, thus keeping everything in the digital domain and thus eliminating a source of variation?
 

ElectricPhase

Power User
I'm guessing that Cliff, in a characteristic moment of enthusiastic pride, posted a screencap pulled out of a very extensive testing regimen. I doubt that it was intended as scientific proof of anything. I see it more like Dad passing around snapshots of the grandkids. It's probably unreasonable to extrapolate from that to the degree that's being attempted by some on this thread.
 

NeoSound

Fractal Fanatic
Yes! Now we're getting somewhere. The issue here is that while the Axe models may exclude analogue thermal noise, the assumption in Cliff's post is that the Helix does too. Personally, I'm absolutely cool with the flaws of the original amp's topology being represented in the modelling...I can understand why other folk might not be, but the assumption that it must be aliasing isn't supported by the data presented because - as I've said repeatedly - there is no "control" plot, which would be an amp of the original model. It wouldn't be perfect, because it wouldn't have been the specific amp being modelled (we all know that 1950s tech can be variable at best...just ask Nuno about the amp he used on Waiting for the Punchline...), but it would give a big pointer to that.



No, to my knowledge, there is no such thing as an aliasing analyser - that was kind of my point. Apologies if I didn't make that clearer :)

As above - if you assume that the Axe noise floor is that low (I haven't seen evidence, but I can well believe it) and you assume that the Axe's modelling deliberately discards bits of the original amp's signal that aren't deemed desirable (like the thermal noise, poor signal path isolation etc), then yes...that works for the Fractal gear. I'm not so sure about your other suppositions, though; whenever I've encountered ground loops the hum has been much more apparent than any hiss introduced from multiple gain stages at high signal volume. However, we don't really have a frame of reference here, which is why I was asking for more details on the test setup so it could be replicated.



Definitely with you on the weight thing; my whole rig weighs about 25kg 'cos I'm a broken shell of a human being and any more would mean I'm sitting in a wheelchair on stage every night ;)

As for the rest of it...that's down to taste. I'm firmly of the opinion that a lot of amps - particularly older ones - sound the way they do because of the flaws and stuff that are mild annoyances, but add to the subtle differences in behaviour.



I'd like to know more about it, so I can try to run these tests myself and work out what's aliasing and what's deliberate. I don't think anyone's misunderstanding stuff, really, because there isn't enough information presented to get to any conclusion at all.



For my part, I think I've already explained that up there ^^. I don't have a zeal for it, I'm just aware that it presents an explanation for the noise across the spectrum which is a plausible alternative to Cliff's assumption that it must be aliasing and therefore poor design.



As my history teachers always used to tell me..."Consider the source". Cliff has a very obvious vested interest here, so - from somebody who really have an axe (heh) to grind either way* - it pays to be somewhat skeptical when presented with contextless information that doesn't seem to stack up with real-world experience. I'm more than happy to be proven wrong, but I want it to be proven for the sake of improving my own knowledge.

However, I think a healthy skepticism is always a good thing.

* Yes, I own a Helix LT, purely because I can't afford an AxeFX to be able to compare it to at the moment, and a rack unit wouldn't suit my current needs. If there's something better out there for my needs, though, I want to know about it - and that's what this is about, wanting to know more. The Helix is my first Line 6 product since the POD 2.0, so I'm by no means wedded to the brand...in truth, my audio needs amount to "Does it do a really good impersonation of a SLO?", which is probably significantly less onerous than what you guys do with it.



Also an excellent question, and something to be borne in mind. In fact, while we're at it, why not ask the question of the one that kicked all this off - why, when measuring aliasing, was an analogue signal path involved at all (at least with the Fractal units, given the ground loop) when the modelling could've been directly tested via USB without passing through the converters, thus keeping everything in the digital domain and thus eliminating a source of variation?

You have no data to back up anything you say, yet you state your opinions as fact? You’re not a reporter are you :p

As far as FAS and Cliff, we’re sure most companies exist to make money and be successful. If you had been around here long enough though you would have noticed that FAS has went well above and beyond just turning a profit. Who do you think is responsible for the free updates you get for your beloved helix? Other companies sold that luxury to you in the past, hmmmm....
 

vangrieg

Power User
I believe the "isolating effect" is that the Axe models exclude analog thermal noise from the modeled amp

But it introduces its own thermal noise from analog circuits though, and converter noise as well. I’m not sure why this noise would be different from that of an amp. Interference may be different but thermal noise is thermal noise, isn’t it?
 

vangrieg

Power User
I'm guessing that Cliff, in a characteristic moment of enthusiastic pride, posted a screencap pulled out of a very extensive testing regimen. I doubt that it was intended as scientific proof of anything. I see it more like Dad passing around snapshots of the grandkids. It's probably unreasonable to extrapolate from that to the degree that's being attempted by some on this thread.

Haha true. Unlike seeing pictures of some random grandkids, this stuff sparked my curiosity though. :)
 

digitalscream

New Member
You have no data to back up anything you say, yet you state your opinions as fact? You’re not a reporter are you :p

As far as FAS and Cliff, we’re sure most companies exist to make money and be successful. If you had been around here long enough though you would have noticed that FAS has went well above and beyond just turning a profit. Who do you think is responsible for the free updates you get for your beloved helix? Other companies sold that luxury to you in the past, hmmmm....

No, I'm not stating my opinions as fact. I'm stating alternate explanations (hypotheses, if you will), which could be proven (or disproven, of course) with more details about the original tests since the information provided isn't sufficient to support the conclusions given. I'm not sure how I could possibly make that clearer than I already have...?

Look, I've tried to avoid saying it, but we all remember the "facts" that Cliff chucked about regarding the Kemper - like the "it runs at 22kHz and can't reproduce anything over 11kHz" one which was proven false several times over. With that in mind, it strikes me as sensible for those of us who want actual solid facts to maintain a decent level of critical thought instead of just believing a potentially-biased source who's been unreliable on the subject of other companies' products in the past.

My one constant in this is that I've been asking for more information, so that I (or others) can run the same tests to reproduce them and possibly expand on them. You (and a couple of others) seem to actively want to discourage such questioning, which I find rather odd.
 
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NeoSound

Fractal Fanatic
No, I'm not stating my opinions as fact. I'm stating alternate explanations (hypotheses, if you will), which could be proven (or disproven, of course) with more details about the original tests since the information provided isn't sufficient to support the conclusions given. I'm not sure how I could possibly make that clearer than I already have...?

Look, I've tried to avoid saying it, but we all remember the "facts" that Cliff chucked about regarding the Kemper - like the "it runs at 22kHz and can't reproduce anything over 11kHz" one which was proven false several times over. With that in mind, it strikes me as sensible for those of us who want actual solid facts to maintain a decent level of critical thought instead of just believing a potentially-biased source who's been unreliable on the subject of other companies' products in the past.

My one constant in this is that I've been asking for more information, so that I (or others) can run the same tests to reproduce them and possibly expand on them. You (and a couple of others) seem to actively want to discourage such questioning, which I find rather odd.

I find it odd that you remember older posts by Cliff but you only have a few here on the forum yourself?
 

digitalscream

New Member
I find it odd that you remember older posts by Cliff but you only have a few here on the forum yourself?

...perhaps because I can read, and I've never felt the need to post before?

I've always been curious about modelling, because I see it as the path to a future where guitar gear is more reliable, more efficient and lighter.

I'm also no stranger to forums (been a member of a couple of guitar communities since before this one even existed), and that particular incident got quite a lot of attention so it was the first thing that came to mind when I saw this one.

It's the return of the undead shills!

Who, exactly, am I supposed to be shilling for? Avid killed the 11R (which I sorta-kinda liked), the Kemper setup doesn't work for me, Atomic gear makes me laugh, Headrush appear to be a bad joke as far as I can tell, and while the Helix is the current best choice for me it's the only product of theirs that is...I've already said I'm not wedded to their brand and would jump tomorrow if something better suited to my needs came along.

It's quite sad that you have to insinuate that I'm a shill when all I'm doing is asking questions nobody appears willing or able to answer.
 
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NeoSound

Fractal Fanatic
...perhaps because I can read, and I've never felt the need to post before?

I've always been curious about modelling, because I see it as the path to a future where guitar gear is more reliable, more efficient and lighter.

I'm also no stranger to forums (been a member of a couple of guitar communities since before this one even existed), and that particular incident got quite a lot of attention so it was the first thing that came to mind when I saw this one.



Who, exactly, am I supposed to be shilling for? Avid killed the 11R (which I sorta-kinda liked), the Kemper setup doesn't work for me, Atomic gear makes me laugh, Headrush appear to be a bad joke as far as I can tell, and while Line 6 is the current best choice for me...I've already said I'm not wedded to their brand and would jump tomorrow if something better suited to my needs came along.

It's quite sad that you have to insinuate that I'm a shill when all I'm doing is asking questions nobody appears willing or able to answer.

Since you stated that you own the helix lt because you can’t afford the helix, why do you feel the need to post something about a device that costs twice as much? Then complain there’s not enough info or science to perform your own tests with hardware you obviously don’t have?

Hopefully you’re sincere in your interest for the future of modeling but you seem to be more interested in an argument atm?
 

digitalscream

New Member
Since you stated that you own the helix lt because you can’t afford the helix, why do you feel the need to post something about a device that costs twice as much? Then complain there’s not enough info or science to perform your own tests with hardware you obviously don’t have?

Hopefully you’re sincere in your interest for the future of modeling but you seem to be more interested in an argument atm?

That's my current situation; it hasn't always been thus, it's just that my priorities at the moment don't involve the need for a better solution. What I can afford is the time to gain more knowledge, which is precisely what I'm trying to achieve here. The OP is very much aligned with that interest, hence trying to work out the variables and what could be behind all of this.

Basically...my current economic priorities have absolutely no bearing on my desire to know more about stuff. You should also note that I'm perfectly open to the idea that I'm wrong, but from what I've read (here and elsewhere) I don't believe I am...at least, not completely ;)

Finally...yes, I've said in many other places that I believe that the digital world is where everything's headed, not least because valves are expensive and inefficient to produce, and it won't be long before they're priced beyond the reasonable range of the average musician (whether because they're no longer economical to make at high enough quality, or because environmental legislation slaps exhorbitant taxes on them).
 

iaresee

Administrator
Moderator
TrueRTA is a spectrum analyser, not an aliasing analyser.
WTF is an "aliasing analyser" [sic]? Aliasing analysis is a technique, not a tool. And you do it with anything that can handle frequency-power plots, which TrueRTA does with aplomb.

You talk about a lot of things. I have my doubts about how much you actually understand...
 

digitalscream

New Member
WTF is an "aliasing analyser" [sic]? Aliasing analysis is a technique, not a tool. And you do it with anything that can handle frequency-power plots, which TrueRTA does with aplomb.

You talk about a lot of things. I have my doubts about how much you actually understand...

If you take the time to read the rest of the thread, you'll see that my reference to an "aliasing analyser" was somewhat tongue-in-cheek, because everyone seemed to be making the assumption that the extraneous frequencies could only be aliasing, whereas my hypothesis is that aliasing is not the only possible explanation. That you didn't get that kinda proves my point, really - context is everything, and context is exactly what I've been asking for this whole time.

And yes, I spell it "analyser" because I'm British, and it's our language :D

EDIT: I'm going to bed now because my head's full of nasty gunk, so please don't be too offended if I don't immediately respond to any more insults you want to chuck my way... ;)
 
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FractalAudio

Administrator
Fractal Audio Systems
Moderator
Look, I've tried to avoid saying it, but we all remember the "facts" that Cliff chucked about regarding the Kemper - like the "it runs at 22kHz and can't reproduce anything over 11kHz" one which was proven false several times over.

That was not proven false. There was a huge disinformation campaign launched to discredit my findings and I stand by them. That said, their latest firmware does not exhibit that behavior.
 

stereotactic

Experienced
But it introduces its own thermal noise from analog circuits though, and converter noise as well. I’m not sure why this noise would be different from that of an amp. Interference may be different but thermal noise is thermal noise, isn’t it?

I'm sure real analog hi gain amp thermal noise is much louder than anything from the Axe converters, or the analog part of the Axe in/out. I'm shocked at how quiet the Axe is. I can't hear anything right next to the speakers except the lowest level AC line hum when running it through my Matrix amp. The thermal noise of my Mesa 2/90's are only slightly more, thanks to the excellent work of my amp tech. I still have to put my head right up to the speakers, but it's all coming from the tubes and gain stage, not the Axe.

I guess the real question, speaking to the naysayers, is whether aliasing noise has a distinctive signature on an RTA such that it can be visually distinguished from other "noise". That being said, while the Axe does not appear to have much of any original thermal noise modeled into their high gain amps, I doubt other manufacturers model in the full compliment of thermal noise and high gain hiss present in say a JCM 800 modded with an extra gain stage.

So, can we tell thermal noise apart from aliasing in an RTA spectrum? I don't know, maybe Cliff or someone else can explicate...
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
So, can we tell thermal noise apart from aliasing in an RTA spectrum? I don't know, maybe Cliff or someone else can explicate...

Yes, you simply capture the spectrum without applying any stimulus. That's then your noise floor. Then you apply a stimulus (i.e. a sine sweep over a small range so that you can discern aliasing from natural harmonics). The "noise" floor will increase. That noise is aliasing noise.

This is basic stuff and anyone arguing against the validity of the technique and results simply doesn't understand the theory and the math.
 
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