The Aliasing Problem

  • Agreed about the high end, from an artistic standpoint. I thought you had boosted the treble, to make the issue easier for us to hear. Is this a single coil, low output guitar?


    I normally use a PA speaker. If it is easier to hear when using a guitar cab, have you tried using profiles that were created without a cabinet, with the Kemper cab "on"? If not, try some of those, and see if that solves your problem.


    Culd the distortion be coming from overdriving the input to your power amp with the Kemper?

    No, didn't boost the treble, I left exactly as it was in the profile. (which again, was chosen for the extreme signs of aliasing)
    What you heard before was a DiMarzio Evolution bridge humbucker, so not even low output. Anyway, I put new clips (see below) also with lower output humbuckers. I guess the alder gives it a very bright tone.
    I have used "preamp only" profiles: one I created myself based on my head, and that - though not completely alias-free - behaves fairly well; the others I tried, downloaded from the Kemper webpage, also show a lot of aliasing (the dirty tones, of course).
    Finally, I am not overdriving the power amp, and the clips prove it, as I recorded them directly from the Kemper's outs.


    Now, update:
    I made new clips. Hum-free this time, which makes the aliasing really easy to hear this time, both with and without cab simulation.
    I used two Yamaha Pacificas, one with a DiMarzio Air Classic pickup (bridge, medium gain) and one with a DiMarzio Evolution (bridge, high gain), and I made a clip for each combination guitar-cab sim on or off.
    I loaded the clips here: https://soundcloud.com/simone-frau-2/sets/new-alias-clips
    and you can also download the wave versions from here: https://drive.google.com/folde…94cS1KUFNCNEU&usp=sharing


    I tried profiling a lowpass filter (plugin on my pc), the result did not help much: although the filter was set at 20kHz, the overall sound appeared somehow a bit muffled and still retaining the aliasing.
    But this is a hardly reliable try:
    1) the PC plugin has a noticeable latency, the profiling might all broken in such a scenario I believe
    2) the cab is not the profile that I made, but a part of it that the Kemper estimates to be the cab part of the profile. The result is to me completely unpredictable (and most likely irrelevant in our analysis)


    So, enjoy the extremely boring clips :P

  • Well... That does sound like aliasing, doesn't it...


    Did you record through the SPDIF or the analogue outs?

    Analog outs. The "cabbed" version from the Main out, the "uncabbed" version from the Monitor out.
    I am actually surprised that I am the only one to bump into this problem...noone using it for high-gain sounds?

  • I had had a problem like this and a system reset cured it.

    Seriously? That would be gorgeous. I guess I'll ask confirmation with their support team first (in case they actually need to analyse the setup and I can provide some helpful info)

  • Yeah, using some high gain sounds but luckily I don't have this problem! Tried most of what's loaded into my Kemper. So, it must either be specific to some profiles, or it must be your Kemper...


  • Do you have the possibility to try S/PDIF?


    No wait... I'm thinking that maybe the problem COULD be from the audio interface, but did you say you experienced the same through a real cab/FRFR (i.e. without going through the interface)?

    Yes, both on record and (most of all) "live" (well, in my room, but going to an actual guitar cab). No AI in between.

  • I suffer from folic acid deficit which some times leads literally the tip of my nails to detach from my skin, and that hurts like a bitch.


    I have read that when this happens, as it does especially to acoustic playing musicians, they use Crazy Glue to glue the skin back to the nail with great success.


    There is even a form of it used essentially in surgery to close wound in a stitch less way.


    Have you tried it? Might really help you, and sorry you have to go through that. I have been through it once and it is very painful.

  • ma that clip is about as fizzy as it gets.. so I've got a couple of passages on a track or two that sound similar.. guess I'm having an aliasing issue as well. Thanks for point ing it out.. What I've don in the past is switch guitars.. it seems more dominant on my cobra, which has a 6 ohm front pickup.. when I move to a gibson with humbuckers, the issue seems to go away.. (using the same profile)

    Gettin' funky up in here..

  • I had had a problem like this and a system reset cured it.

    Tried resetting this morning: didn't change a thing. (It would have surprised me a lot if it did)

    I have read that when this happens, as it does especially to acoustic playing musicians, they use Crazy Glue to glue the skin back to the nail with great success.


    There is even a form of it used essentially in surgery to close wound in a stitch less way.


    Have you tried it? Might really help you, and sorry you have to go through that. I have been through it once and it is very painful.

    Oh man, if that would work I'd owe you for the rest of my life!
    Each time I have to stop playing for some 2-3 days, and even when I restart for some time I need to be all cautions with vibratos lest the wounds would open again :(
    But is this Crazy Glue the generic supertough glue that you can find anywhere? I would be a bit concerned whether it's totally safe to put that on something that is quite like a wound (even though it doesn't bleed).
    Maybe I can double check with friends of mine that are doctors.

    ma that clip is about as fizzy as it gets.. so I've got a couple of passages on a track or two that sound similar.. guess I'm having an aliasing issue as well. Thanks for point ing it out.. What I've don in the past is switch guitars.. it seems more dominant on my cobra, which has a 6 ohm front pickup.. when I move to a gibson with humbuckers, the issue seems to go away.. (using the same profile)

    Yes, it is a very fizzy rig. I would probably never use that one particularly for myself, but still I go very high gain though not as "modern".
    If you're having aliasing or not, you shouldn't judge from the fizziness of the rig (though those are certainly the conditions where you could expect it the most) but from listening. Try plugging it on a guitar cab, cab sims off, and play a single, sustained high note with some vibrato, that's when you hear the craziest wobbling. If you don't hear anything there, you should be fine. If you do but it's fairly subtle, you might be ok when cab sims are on (but do check closely with headphones on your record).


    Certainly the guitar/pickups used is a factor, but I find it really hard that it would go away altogether just changing guitar. I have tried with the two Yamaha Pacificas (used for the clips, DiMarzio Air Classic and DiMarzio Evolution respectively) and then with an Ibanez J Custom 7 string, with some custom DiMarzio PafPro (or similar)...the latter showed less signs of aliasing, in line with the fact that it is a much less bright sounding guitar, but nonetheless it was still there and not very attenuated either.

  • Update from Kemper support:


    I managed to recreate the situation on my system and forwarded the case to our developers.
    Please wait until i get their comments.
    As soon as i have new info i will get back to you.
    Thank you for your patience.



    So prompt and kind intervention. Another plus for Kemper!


    Now we wait and see :)

  • Updates from Kemper team:


    I just received the information from our developers that the Aliasing problem will be fixed in the next firmware version.
    Please let me know if it works or you once it becomes available.


    needless to say, I was already falling in love big time with this company, now I think I wanna get married and have kids with them

  • BTW, can anyone tell me how you do FFT analysis of wave files? Sure, I could google that, but I want to hear how you do :P
    Or, also, if you use other tools for spectrum analysis

  • BTW, can anyone tell me how you do FFT analysis of wave files? Sure, I could google that, but I want to hear how you do :P
    Or, also, if you use other tools for spectrum analysis

    I have adobe audition which has the feature built in. I am sure there are free tools out there that would do this though. Audition is not cheep.

  • I have adobe audition which has the feature built in. I am sure there are free tools out there that would do this though. Audition is not cheep.

    Yeah, I am indeed not purchasing Audition for that alone :P
    Thanks though, it's interesting to know