Be aware of the digital sonic artifacts (aliasing) in your KPA!

I am sure we'll get an official answer - we got it for all issues up to now.

Just send a mail to Kemper, cause I would like to know what´s going on. Worst case (may be I´m thinkin nonsense, but I´m just a user and analog tube worker ) : What, if that problem is software problem, and is so part of profiled rigs with that software?

i was playing with headphones for a change (cab sim back on) and not hearing this. so i even tried recreating it again and still was not hearing it anymore. i didn't do exhaustive testing or anything, but turning cab sim back off made it return in spades in the headphones (along with ice-pick-to-the-ears™ sound - turn way down if you want to try this)

so i wonder if everyone hearing this is running (like me) with cab sim turned off and the filtering in the cab sim is clearing it for the others...

But then you would not hear it recording direct (cab sim on)... I personally never head it, but I can hear it on the clips...

I hear it plain as day with or without cabs on.

I get these artifacts only in case of:

1) Drive above 15:00
2) Profile is quite bright
3) Playing on the high E string above the 12th fret

Is here anybody having these artifacts with low gain settings or on the lower strings?
On the other hands the users without these problems may use lower gain sounds or play on the lower strings.

And yes, this are KPA artifacts and no problems from the guitar, fret noise or whatever - I use a profile of my Rectifier and compare it with the real thing - the Rectifier has no artifacts the KPA has,

The real amps do not have these noises. I checked out different tube amps, and gave en extra power with OCD or other boosters/overdrives, ..... yes there is noise, and some weired harmonics coming, but not those digighosts! We need some ghostbusters now!

I get the digighost notes als on lower strings, depending on profile, gain, settings ....... ! Seems as the software or the hardware (and would make to a problem for me) can´t handle these extreme multi frequenz tones, and holding up the white flag on these.

Solving (if possible) sound quality problems should be set on highest priority at the Kemper team, as a workstation like the KPA that is restricted by such problems should be a no go! If not possible to solve that ............. I don´t know yet what to think about that in such a case.

Quote from ACY

as a workstation like the KPA that is restricted by such problems should be a no go! If not possible to solve that ............. I don´t know yet what to think about that in such a case.

So, all the KPA users around the world, engineers, producers, guitarists, that are recording and gigging with their KPAs, and not being affected by this "aliasing" should stop using their KPAs?

In the Anderton KPA Profiling video done by Rob Chappers, they profile a Cornford Carrera.
Chappers demos the profiled Cornford against the real amp.
He notes that the real amp has a problem when soloing on the low strings, the low notes choke and cut out, he also notes that the Kemper Profile corrects the problems the real amp encounters.

Is the Cornford Carrera a "no go"?
I don't think so.
Anyone who owns a Cornford Carrera should be aware of the problem it has in that particular area, on the low strings, high gain soloing, and avoid the problem, or ignore the problem.

Just my opinion, but this "aliasing" problem is being given way too much attention...IMO.

You are absolutely right, it is given a bit too much attention.
However it is definitely there, and might be intolerable when playing special types / styles of music.
As this phenomenon is a characteristic feature of old, low-end digital units, at least some official statement would be very welcome.

As long as it is not solved, and no information about actual status is made, it needs attention.

Aliasing is not really depending on Hardware structure or software algorithms or programming skills.
It is only a matter of the simple speed of the distortion algorithms and the calculation power consumed by that.

Therefore I found it a bit distracting that a competitor makes comparison tests about aliasing - as if less aliasing was a technical innovation.
Probably the comparison was done to justify the use of a loud fan and the high price

If I felt face to face with them - I mean mentally - I would rather start a revealing comparison about innovations and sound dynamics and so on.
But I think that is not a mature way to deal with competitors.
So, back to the topic.

Aliasing cannot be avoided in digital guitar amps, there is no amp simulation without aliasing. It is just a matter how loud it is.

The Profiler produces a bit of noticable aliasing on the highest notes of the guitar, or by harmonics.
Those are not noticed by a majority of users, that is why we have our algorithms set as they are.
You need to use artificial test tones to make the aliasing more obvious.
This aliasing virtually non existent on deeper notes or chords, or in a band or recording mix.
That is why we think we have found the right balance.

Half of the comments in this thread are obviously not about aliasing.
Aliasing is created by very high notes through heavy distortion only!
Aliasing does not occur on clean or crunch sounds, and not with deeper notes or chords.
If your problem does not fall into this category, you should post an audio clip.

We have a large headroom of calculation power left, that I was planning to keep for future features and improvements for upcoming firmwares.
However, it takes only three seconds for me to speed up our algorithms for the next firmware.
But this would eat up some of the headroom for the future.
Still we don't know how much headroom we will use in the future.

What do you think?

CK

I think that the best idea should be to implement an "anti-aliasing" option...

It´s right, only higher gain settings, but still you can find these on lower strings/notes too, when playing very agressive pinch harmonics, may be the sort of pick is also part of that story. (using ultex sharp picks)

When I get you right it´s not possible to avoid the aliasing, only working on volume of these? And that´s going on cost of calculation power, if speeding up algorithms to lower aliasing volumes?

If I understood that right, would´nt it be possible trying to get a compromise with some more lower aliasing volumes? I find them too loud, may be not noiceable in a 2 guitar, bass, drums ........... mix, but a one guitar band and guitar loud in the foreground I see problems with actual volume of aliasing.

PS.: Thanks for clearing up this issue, good to know more facts about that now.

Quote from ballantine

I think that the best idea should be to implement an "anti-aliasing" option...

...together with a Line6 style "DSP limit reached" message when trying to use some of this future features. If technically possible it could be a solution...

Quote from ckemper

Aliasing is not really depending on Hardware structure or software algorithms or programming skills.
It is only a matter of the simple speed of the distortion algorithms and the calculation power consumed by that.

Therefore I found it a bit distracting that a competitor makes comparison tests about aliasing - as if less aliasing was a technical innovation.
Probably the comparison was done to justify the use of a loud fan and the high price

If I felt face to face with them - I mean mentally - I would rather start a revealing comparison about innovations and sound dynamics and so on.
But I think that is not a mature way to deal with competitors.
So, back to the topic.

Aliasing cannot be avoided in digital guitar amps, there is no amp simulation without aliasing. It is just a matter how loud it is.

The Profiler produces a bit of noticable aliasing on the highest notes of the guitar, or by harmonics.
Those are not noticed by a majority of users, that is why we have our algorithms set as they are.
You need to use artificial test tones to make the aliasing more obvious.
This aliasing virtually non existent on deeper notes or chords, or in a band or recording mix.
That is why we think we have found the right balance.

Half of the comments in this thread are obviously not about aliasing.
Aliasing is created by very high notes through heavy distortion only!
Aliasing does not occur on clean or crunch sounds, and not with deeper notes or chords.
If your problem does not fall into this category, you should post an audio clip.

We have a large headroom of calculation power left, that I was planning to keep for future features and improvements for upcoming firmwares.
However, it takes only three seconds for me to speed up our algorithms for the next firmware.
But this would eat up some of the headroom for the future.
Still we don't know how much headroom we will use in the future.

What do you think?

CK

Display More

This has nothing to do with what your competitor is saying. I don't think you should be asking us what to do. The people that do not hear it probably will tell you not to bother about it and that would be a bad advise. In my opinion your first priority should be to improve or fix what is not completely right, specially if you still have a large headroom of calculation left. As more people get the KPA the more people will notice it and you will be constantly reminded about it. This is the most visited and participated thread on the forum and that should tell you something.

Quote from ckemper

he highest notes of the guitar, or by harmonics.
Those are not noticed by a majority of users, that is why we have our algorithms set as they are.

CK, I never noticed the aliasing yet, maybe because I am not such a high gain player but I am super anal about tones and quirks (I usually notice faults right away) and the Kemper is the only digital modeling device that I have ever been satisfied with and actually kept. I use it on a daily basis. Your response to this entire thread shows the Kemper community what a class act you are, admitting the fact that aliasing exists (even though I don't experience it) and that you prefer to handle the competitors in a more mature fashion. I'm not saying you walk on water, I don't want this community to turn into a cult with a worshipped "God" like other communities have done. The headroom is an important factor in the Kemper and I think that is what leads to the realistic "feel" this unit has, I would be bothered to see that suffer but I also don't want the men who solo above the 15th fret with uber gain to suffer either, I may even join a Twisted Sister tribute band someday, there must be a balance somewhere....

I think Christoph referred to the headroom of the processing power. Not in a "tonal" sense.
Anyway, thanks for the insight.

Between more features and less aliesing I vote less aliesing..I can hear it..it's not terrible but still too much for me in certain rigs

Quote from donbarzini

CK, I never noticed the aliasing yet, maybe because I am not such a high gain player but I am super anal about tones and quirks

Only for fully grown man

By the way, i have no aliasing issue too, since I don't use too much gain.
I like the idea of the anti-aliasing filter: i wonder if you might implement it as a stompbox, in order to "suck" enough DSP to reduce the issue for people who feel uncomfortable. Just like a DSP booster, if I have explained my idea.