pulse or aliasing noise

    Summarizing from another thread:


    I have been noticing lately something wrong when playing with a considerable amount of gain. It happens more when I play the highest frets on the 1st string. There is some sort of pulse or aliasing noise. I am talking about playing single notes.



    Also when I use a headphone amp connected by spdif that has the capability to oversample the input, I am able to make this issue even more noticeable by adding/increasing oversampling in the amp headphone. I am not sure if this is the same thing Radley is referring to but there is something not right there and quite annoying.


    I recorded a couple of clips to demonstrate it. Each clip is recorded with a different profile. The 1st one with the Fargen 80's profile (unedited) and the 2nd with the profile Bogner XTC CH3 Boost from r.u.sirius using Tills cabs. 2 different guitars were used for the clips. This happens with digital, analog outputs and headphone output. You can easily hear something weird going on the high end. It feels like a pulse of some sort or maybe aliasing.


    I don`t think it has anything to do with the profiles being damaged. I used two profiles as example but I tried to do this with many profiles including stock ones and I was able to replicate the results. It only seems to appear with a considerable amount of gain and playing on the highest notes of the 1st string, like you can hear on the clips.




    http://soundcloud.com/mad_h/sets/kpa-issue-clip-1



    To try to replicate the issue you can try starting with the fret 14th on the 1st string for instance and continue from there until the last fret, playing one by one. It does not happen in all the notes. You just have to hit the notes with the pick with a strong enough attack (no vibrato). I know it is not my guitar because I tried with 3 guitars (2 guitars used on the clips). I used two different nice cables (Evidence HG Lyric and Evidence Melody).


    This is the profile I used for the 1st clip http://dl.dropbox.com/u/744445…012-04-13%2000-13-22.kipr and this is the one for the 2nd clip http://dl.dropbox.com/u/744445…012-04-13%2000-13-22.kipr




    I noticed that increasing the gain makes the issue even more noticeable. After you try that one you may try as well with other profiles including stock ones as well as long as you have the gain at 6 or more and a cab that allows enough high end to go through.



    Btw, I am on firmware 1.08 beta (tried with 1.07 as well). Also tweaking clean sense does not make any difference.



    I sent CK the 2 profiles as he requested in a different thread and I am waiting for his answer about it.



    Could someone try to replicate this and share the results?

    Edited once, last by MadH ().

    Quote from MadH


    Also when I use a headphone amp connected by spdif that has the capability to oversample the input, I am able to make this issue even more noticeable by adding/increasing oversampling in the amp headphone.

    What is that headphone amp? Interesting that it can change a sound by oversampling.

    Quote from MadH

    I am not sure if this is the same thing Radley is referring to but there is something not right there and quite annoying.

    No, it's not the same.

    No, there is nothing in between. I tried with 3 different guitars and 2 different cables. I tried as many things as I could to discard any possible external cause. Btw, I added links in the previous post for the 2 profiles I used on the clips.

    Quote from ckemper

    What is that headphone amp? Interesting that it can change a sound by oversampling.

    It is a headphone amp (http://www.audio-gd.com/Pro/Headphoneamp/NFB12/NFB12EN.htm) I bought it to use it with my Sennheiser hd 650 headphones due to the impedance used by the headphones. It has a DAC incorporated with oversampling and filtering capabilities. Increasing the oversampling on the headphone amp makes the issue for noticeable. I just included that comment just in case it helps you to identify the issue.

    Quote from billruppert

    I get similar noises up high on my guitars with Floyd Rose bridges and other trem bridges.
    Its the movement of the bridge and springs as you pick.
    Pure mechanical on my guitars.

    It is not due to that in my case. Like I said it does not happen with my amps or other modelers. It is not due to the usual buzzing, spring noise or string warbling that you can get with tremolo bridges.

    Good news!!!


    If somebody else suffers this issue this is what I did. I did a complete reset on my KPA since I did not know what else to try. The issue I was having seems gone now. I don't know if somehow all or most of my presets were corrupted or if it was something completely different but it is fine now. Thanks to CK and everybody else for their help.

    Quote from MadH

    Good news!!!


    If somebody else suffers this issue this is what I did. I did a complete reset on my KPA since I did not know what else to try. The issue I was having seems gone now. I don't know if somehow all or most of my presets were corrupted or if it was something completely different but it is fine now. Thanks to CK and everybody else for their help.

    Complete reset = booting while holding System?

    Use your ears, not your mathematical sense.

    Quote from MadH

    Yes, but I have also restored all my presets from a backup.


    Ok, so to summarize: you erased everything, did a system reset and loaded a backup and everything was fine?
    Please explain exactly what you did (might be important for other users and also for Kemper)

    Deleted everything, system reset and then I restored a backup of my rigs. I don't really know if the problem was caused by something on the system or the rigs but if someone else has the same issue they can try what I did.

    Ok, thank you.


    So, for the newcomers:


    If you encounter a digital aliasing or pulsing issue with your KPA, this is what you should try.


    A, Turn on your KPA while holding the System button. This is a reset of your KPA's software, and you don't lose any rigs in the process.


    If this didn't help:


    B,
    1. If you have a backup already, it's ok, but if you don't, make a backup of your current rigs.
    2. Delete every rig from your KPA either manually or by formatting it. If you choose to format, you might not need to go through the following steps. If you choose to manually do it, continue.
    3. Turn on your KPA while holding the System button. This is a reset of your KPA's software.
    4. Restore your rigs from your backup.

    Use your ears, not your mathematical sense.

    Wow. I'm glad you figured it out and really happy for you. I wonder if this is why some users report that their KPAs have these dealbreaker tone issues while others think it's the greatest thing. So the former are not just haters and the latter are not fanboys. And clips are extremely important! If you have a problem, do a system reset reset first!

    I think sometimes is due to issues produced by the KPA firmware not being stable enough but most of the times I believe it is due bad profiles. In my case it was due to the first but I will not complain since I have been using beta firmwares, and you have to understand what that means.


    There are profiles that are simply terrible, like they were not refined and tested properly before their creators shared them. I created one profile that primarily seemed to sound perfect. Then later on I noticed that when I played a particular note with a bending it produced a really annoying squeaky tone. I redid the profile and then it was fine but if you don't test them properly you might encounter problems later on or have other users suffer them.


    Maybe part of the problem is that when people sees the marketing videos, the process seems easier than what it is. So people expect to get stellar results in 5 minutes with no previous experience with real amps miking, recording, etc... or don't understand the type of sound they are going to get. The recurrent "amp in the room" subject.