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

  • I never noticed it myself in my normal playing but I a) have ears of stone and b) wasn't listening THAT closely to the background underneath sounds. Pretty odd sound in that clip you posted. I'll listen closer and see if I hear it now.

  • I intentionally played straight and sterile so as to make the noise somewhat obvious even though it's kinda subtle upon first examination, in order to bring attention to the issue... I find it more audible when I'm actually playing rather than listening back to a recording, because I can almost interact with the noise. I think more players will begin to notice it now--I got the impression that Kemper didn't know about this when I contacted them, or maybe they did but didn't let on to it until I fully presented my observation.


    This noise will most likely effect players (like me) who love to play high-gain, sustaining, slow, melodic leads, unaccompanied, probably in a studio or quiet room, and want to get-off on the sonic purity of the KPA, but it turns into ants at the picnic.


  • This noise will most likely effect players (like me) who love to play high-gain, sustaining, slow, melodic leads, unaccompanied, probably in a studio or quiet room, and want to get-off on the sonic purity of the KPA, but it turns into ants at the picnic.

    Watch this video.
    Skip straight to 40:25 on the video, listen to what Rob Chappers says whilst playing the Cornford Carrera Profile.


    http://www.youtube.com/watch?v=mAuY9OyMsdg

  • Watch this video.
    Skip straight to 40:25 on the video, listen to what Rob Chappers says whilst playing the Cornford Carrera Profile.


    http://www.youtube.com/watch?v=mAuY9OyMsdg

    Good point, Lance. The problem here is that a lot of people are not used anymore to play with real cranked amps and have forgotten how they do really sound, including all related issues....

    "Music is enough for a lifetime, but a lifetime is not enough for music" Serghei Rachmaninoff


  • Here is another sound file of the same Vox profile as my original post but with an added dist stomp which really compounds and emphasizes the noise:


    Another KPA Aliasing Example


    I have some dialed-in studio amps that I want to profile, but I am waiting till this problem is fixed... and I do believe it will be, eventually.


    The big question in my mind is: Is this really a firmware issue, or will I have to wait for a future KPA II HD? Kemper says that they will fix it in firmware, and I take them at their word, but my instincts tell me that it's more about resolution and DSP power, which would mean, hardware! I'm looking forward to the near future when they prove me wrong. Normally, a DSP intensive device runs kinda hot, the KPA runs surprisingly cool.


    Did I mention that I love my KPA?

    Edited once, last by miles ().

  • question:


    do you have a cable plugged into the monitor out as well?


    on some profiles, when I am taking the stereo out, and also have a plug in the monitor out that is not plugged into something, I get added fuzz or noise...

  • question:


    do you have a cable plugged into the monitor out as well?


    on some profiles, when I am taking the stereo out, and also have a plug in the monitor out that is not plugged into something, I get added fuzz or noise...


    So far I have only used the master outputs.


    I tried doing what you are doing with the monitor out, and I can detect no change with the noise level in the master outs or headphone out--not sure why your getting that.

    Edited once, last by miles ().

  • I tried your test and do not get any real difference with or without the compressor added..now I would not say that the sound is 100% distortion free to start with but no (good) guitar amp is, even on a clean sound
    Can you post a clip of this please ?

  • I tried your test and do not get any real difference with or without the compressor added..now I would not say that the sound is 100% distortion free to start with but no (good) guitar amp is, even on a clean sound
    Can you post a clip of this please ?


    Does the distortion sens control have any effect on your result?


    I resolved the issue regarding the clean distortion from the comp by increasing the attack up from 0. This super-fast attack time literally sounded like distortion, and increasing it made it go away. The KPA can actually make a rather squeaky-clean DI with the amp profile off... nice! :thumbup:
    In case your curious, here is what the 0 attack time compressor distortion sounds like--the first 4 strums have no comp, the next 4 strums have the comp with 3.0 intensity and 0.0 attack time, amp off, cab off, presence all the way:


    Clean Test 1


    The high-gain aliasing sound as described at the top of the thread still exists though.

    Edited 4 times, last by miles ().

  • I agree that the aliasing issue is ongoing and tends to reflect negatively on the current KPA package - the Kemper profiling technology is truly groundbreaking, but it is implemented alongside a rather dated box of code. The KPA profiling deserves better than it's current packaging, IMHO...

    All modelers known to man 8o

  • What on earth are you talking about?


    I am talking about a 'support system' with very weak Noise reduction, Stomp ODs with unacceptable amounts of aliasing and noise, an unreliable OS, and totally unrealistic startup times for performing. Now what are you talking about?

    All modelers known to man 8o

  • FWIW, audible aliasing is now a thing of the past for even most moderately priced modelers - it is normally considered a result of poor/incomplete programming.

    All modelers known to man 8o

  • I agree that the aliasing issue is ongoing and tends to reflect negatively on the current KPA package - the Kemper profiling technology is truly groundbreaking, but it is implemented alongside a rather dated box of code. The KPA profiling deserves better than it's current packaging, IMHO...

    Forget about Profiling, how does the KPA produce it's pristine clean tones and organic distortion if it's "box of code" is old & dated?

  • Lance,


    Please don't take me wrong - I believe you and everyone else who has read all my posts know that I want to see the KPA and Mr. Kemper become a worldwide success with this concept! As great as the main Profiling part is, it is laden within a containing OS that does not do it proper justice. The noise, the aliasing, the instability, etc point to the overall system, not specifically the Profiling section, which is the truly new and quality aspect of the KPA...

    All modelers known to man 8o

  • You could say the same about the stratocaster. It's noisy, the trem doesn't stay in tune when you bend more than a little, the sound can be too harsh, to work on the circuit you need to take off everything and some more dowsides. You hear digital artifacts but do not complain about pickup noises, right? Users got around the strats problems somehow or they live with it. The question is always if these points are that important that you can not work with it at all. Now is it a dealbreaker or just one more backroundnoise?

  • You could say the same about the stratocaster. It's noisy, the trem doesn't stay in tune when you bend more than a little, the sound can be too harsh, to work on the circuit you need to take off everything and some more dowsides. You hear digital artifacts but do not complain about pickup noises, right? Users got around the strats problems somehow or they live with it. The question is always if these points are that important that you can not work with it at all. Now is it a dealbreaker or just one more backroundnoise?

    That's not a fair comparison. I understand what Radley is saying. If you are trying to replicate something your main goal is to be as accurate as possible but most important of all is to do not introduce undesired results in the process, like the ones described by Radley.


    I don't agree with the way he express it though and I am pretty sure he has no clue what he is talking about when he says the KPA is a "dated box of code".


    The KPA is the first of its kind and even if some of the issues are similar to the ones in some modellers, I doubt the causes of those issues are the same and can be corrected the same way. If that were the case that would mean that Kemper have no clue what they are doing. When you see what the KPA does and how it does it, that thought simply cannot cross my mind.