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

And these types of responses are what make some of us crazy - this is very easily identified to experienced ears as classic digital aliasing, and it has nothing to do with pickups, or other factors but is a very natural product of sub-par digital processing (we're talking 2012 folks).

I realize it's frustrating, but a guitar note through an amp is a very complex thing with many sounds, harmonics and what could be perceived as undesirable artifacts, so in order to "hear" what it is you're hearing requires first eliminating everything else first.

So to that end, are the ghost notes in this what you're talking about? (you can hear it mostly around the 17th fret in passing but it's elsewhere too) sounds a little like a ballbearing rolling accross a board in the bg : http://www.per-anders.net/general/ghostnotes01.aif (two different settings).

Or are we talking about a phasing sound? Or the bloom in the earlier example, or something else? I don't necessarily have the most sensitive ears, but I would like to help you and Kemper find the solution.

Quote from Radley

And these types of responses are what make some of us crazy - this is very easily identified to experienced ears as classic digital aliasing, and it has nothing to do with pickups, or other factors but is a very natural product of sub-par digital processing (we're talking 2012 folks).

Every week pops up a new topic in this forum that something is wrong with the higher notes played by the KPA.
But none of this threads has a proof (pardon me if there is proof I have overseen)
I do not own a tube amp so I'm not able to prove something is wrong with the KPA.

So Radley you have a tube amp, a microphone and a computer to record?
Then profile your tube-amp
Record a dry guitar track with those high notes
Reamp it with your tube-amp
Reamp it with your KPA
Check for differences

All other discussion is pointless

Doesn't seem to be a problem on the amp block for Radley - post 83. I haven't heard it yet but I only use the stack block - no stomps, no fx, and no noise gate.

It is little bit confusing to have so many isseus in just one thread.
I use only the TS stomp box in the KPA and I have no problems at all.
Radley
You can also profile your high-gain stomp box if the build in stomp box has aliasing. Does this work?
Your noise problem is probably self-made because of the complexity of your chain within the Kemper:
You use a Compressor + High-Gain Stomp + High-Gain amp + NR and complaining about too much noise?
Maybe this works in an Axe Fx but not in the Kemper.
I have played with many modelling amps in my life and they all have things that don't work when it
comes to complex chains and too much gain.
There are also a few profiles with a high noise level which could make things even worse.
But in general the KPA has not more background noise than other modelling amps.
And High-Gain Tube amps have even more noise issues.

Quote from miles

Kemper has acknowledged to me that they are aware of the exact problem I posed at the beginning of this thread, and says they are planning a fix in firmware. Radley is right when he said "this is very easily identified to experienced ears as classic digital aliasing".

Did you get any update on this from Kemper in the meantime?

I kind of dig digital aliasing, it's just another brick in the Wall of the never ending pallet of guitar tones.

LOL! Good one Lance!

Quote from miles

My last email from Kemper regarding this issue was on April 24th--no word yet on the progress.

I was just gonna say "24th? Great, so you got news today!". Then I realized, it's May!!!!
Ok, I would just drop them an email and ask if they have made any progress... hopefully it will clear things up

I† is curious †hat they didn't opt for a more powerful dsp to give more room to grow into if needed.

Quote from Kermit

Every week pops up a new topic in this forum that something is wrong with the higher notes played by the KPA.
But none of this threads has a proof (pardon me if there is proof I have overseen)
I do not own a tube amp so I'm not able to prove something is wrong with the KPA.

So Radley you have a tube amp, a microphone and a computer to record?
Then profile your tube-amp
Record a dry guitar track with those high notes
Reamp it with your tube-amp
Reamp it with your KPA
Check for differences

All other discussion is pointless

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Really??? Actually, I am asking you and a few others to trust the ears of someone who has been working with digital products/modeling since its inception. I heard the obvious digital aliasing in the earliest digital units GP-16,GX-700, POD 1, and I learned exactly what to do to 'expose' it - and that aliasing sound is still as unique as it is irritating - even my M-Audio Black Box (which sounds *great* btw) is plagued with massive amounts of digital aliasing on all OD sounds, rendering it useless. I know this sound like the back of my hand, and it is very present in the KPA's higher gain overdrives, making them unusable for serious recording, imo.

FWIW, I have never heard even a hint of digital aliasing from my Digitech, Fractal, or recent Boss or Line 6 modelers - digital technology is beyond that limitation now, so it's time for Kemper to 'catch up' in this regard.

Radley, could you check my previous post? It's a bit hard to know exactly what the effect sounds like as there's a lot of sounds going on in this stuff.

Quote from Per

Radley, could you check my previous post? It's a bit hard to know exactly what the effect sounds like as there's a lot of sounds going on in this stuff.

Per - The only 'effect' I refer to is classic digital aliasing. There is no mistaking it, and there is no other outside influence that can recreate the same effect - it is unique in it's unnaturalness, and it need not be a part of any serious digital processor in 2012.

Radley you're still being way too obtuse. Either listen to the sample I gave in that post and comment. Or do the comparison someone else suggested. Or just try to actually explain what it is you hear in practical and simple terms, we have no frame of reference for "digital aliasing sound", saying that's what it is and it's "unnatural" doesn't actually explain it, help us see what you're seeing (or hear what you're hearing). Otherwise this is going no-where and everyone is just going around in circles.

I just saw this thread last night, and thought I'd jump in. If somebody else has already posted a similar demo, my apologies.

First, I disagree that in 2012 digital modelling should be so mature by now that everything should be artifact-free. It's really the nature of the beast - you can try to minimize the artifacts, but if you're doing an honest simulation of a high-gain amp some aliasing or foldover images are always going to be present - it's just a matter of how well they've being suppressed. To that end, you can throw more power at the problem (more oversampling! higher sampling rates!) or limit the higher order harmonics generated by the non-linear DSP sections, but it's pretty universal. I used to get a kick out of measuring this and built a set of tools for exactly this purpose but it got kind of old after a while. I think the most egregious example of aliasing i've seen lately was in a BOSS BC-2 "Combo Drive" pedal I put on the lab bench - but you know what? It's a great sounding pedal otherwise, and how often are you listening to screaming high notes all by themselves?

Anyway, here's a pretty pure demo of the effect using the "Wet Queen" patch that began this thread. It contains Four tests of a sine tone fundamental simulating a bend and release from the 22nd fret to 26th fret on guitar (i.e., 1174Hz to 1479Hz, D to F#) using "Wet Queen" digitally reamped via S/PDIF @ -12dBFS.

Pass 1: All Effects Off
Pass 2: Only Stomp "B" enabled (Metal DS Drive cranked to 10 to exaggerate the effect)
Pass 3: Only Stack section enabled
Pass 4: Stomp "B" + Stack section

KPA Aliasing Test Demo

The noticeable thing here is that the distortion pedal is a much bigger contributor to the aliasing distortion than the amp model itself is. I've cranked up its gain to exaggerate the effect, but cranking up the Amplifier's gain is not as obvious as the pedal model. And combined, well - it's pretty clear. You can also hear a few clicks as I'm turning the Stomps & Effects sections on and off - they're not completely noiseless (but perhaps they should be; a 5mS crossfade would solve the problem.)

-djh

Wow, nicely done. The aliasing effect in there would be this fluctuating sound you can hear in the background? I can hear that on the 3rd clip quite low but really fast and on the 4 clips much louder and fluctuating slower.