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

    Quote from Guitartone

    Correct.
    The Kemper has it's own pre-amp.


    Are you sure about that? A mic plugged in directly here gives a volume equivalent to line level, I.e. very very low, there's a multiplier factor on software for the signal, but that just means you raise your noise floor tremendously, it's not a preamp. I see no evidence of a preamp on the KPA and would always recommend that in order to get a good clean signal to your kemper when profiling at anything below 10 or levels where you will encounter distortion in the chain its vital to use a good quality preamp.

    Per: what about using the return volume before to start profiling? It does not have phantom power therefore you cannot use powered mics, but with a normal dynamic mic you need no preamp

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


    I tried your profile, and yes, it has the distortion on it--with headphones on, it is particularly obvious. I don't have any advice to give at this point, so tell me your reason.

    Quote from miles

    I tried your profile, and yes, it has the distortion on it--with headphones on, it is particularly obvious. I don't have any advice to give at this point, so tell me your reason.


    This was an experiment I made to profile a particularly FRFR device : the direct connection. I bypassed everything and connected the 'direct output' of the Kemper to the 'return' (actually, I added a (passive) potentiometer to lower the return signal). This is an experiment everybody can do by himself. So I expected to have a very 'clean' device, with no saturation, and from there, have a flat amplifier, a flat cab, and combine these with existing profiles. But I found that the sound was not really neutral, with always a little bit of distortion remaining, whatever settings I used for profiling. Of course, the sound is terrible if you increase the gain, it sounds like a small cheap transistor amplifier with a lot of clipping.


    Based on this experiment, I don't think that any other device could sound "cleaner" than that when profiled.


    So my feeling is that the sofware of the KPA, in its current state, will always add a touch of non linearity - after all, this is the reason why it was built. It is not a problem in 99.9% of the cases, but yes, it can sometimes be heard.


    Now, have you try to bypass the amplifier, and/or the equalizer and/or the cab, to see (hear) if the artefact is still there ?


    Best regards.


    J. Jacques.


    Good idea, I thought that was what you did, I thought about doing that too. Of course all the distortion is in the amp profile and goes away when you disable the amp. You may be correct in your assessment of the cause, but even though it won't effect most players, it would effect me a tiny bit on certain occasions--I do a wide range of guitar tone applications in my studio, from massive high-gain prog, classic and modern rock, and cleaner low-gain stuff including hyper-clean ambient washes with heavy effects, and that is where I detect it. So I probably will just skip the KPA for that application, and use it on just about everything else.
    The whole point was to highlight a potential limitation (albeit a small one)--I feel like the testing exercise was worthy. I brought this up on this thread because it seemed to constitute a digital artifact, but aliasing is my main concern... just to be clear.

    Quote from miles


    Good idea, I thought that was what you did, I thought about doing that too. Of course all the distortion is in the amp profile and goes away when you disable the amp. You may be correct in your assessment of the cause, but even though it won't effect most players, it would effect me a tiny bit on certain occasions--I do a wide range of guitar tone applications in my studio, from massive high-gain prog, classic and modern rock, and cleaner low-gain stuff including hyper-clean ambient washes with heavy effects, and that is where I detect it. So I probably will just skip the KPA for that application, and use it on just about everything else.
    The whole point was to highlight a potential limitation (albeit a small one)--I feel like the testing exercise was worthy. I brought this up on this thread because it seemed to constitute a digital artifact, but aliasing is my main concern... just to be clear.


    I completely agree with your point of view.


    On the other hand, if you bypass the amp and the cab you get a "flat response device". Then, using the EQ, and possibly one or more Graphic or Studio Equalizer in STOMPS or EFFECTS, you can probably approach some interesting clean tones (may be similar to some very clean amplifier). Now, you can add your "heavy effects", and possibly get the sound you are looking for. I have had some nice experiences with this approach (never saved any snapshot, unfortunately) and found that some effects were quite interesting used this way.


    If you ever try this, tell me if you still detect artefacts, i.e., if you think the artefacts are only due to the "amp" and/or the "cab" part, of if they may also be produced by some of the effects.


    Best regards.


    J.Jacques.

    I do all my effects with pedals and Pro Tools TDM plugins, and I use very few of the KPA stomps, though they are very good (I prefer to use the KPA as mostly an amp/cab only which is why I focus on the tonal purity so much). I think I just saved myself some profiling time with these tests, because I will probably skip the clean profiling and continue using the actual amp for the critical clean recording as I described--though I plan to profile a few higher-gain amps. I wonder if a guy with a golden clean tone like Alan Holdsworth would mind that distortion... hmmm. ;)

    Edited 2 times, last by miles ().

    Quote from miles

    I do all my effects with pedals and Pro Tools TDM plugins, and I use very few of the KPA stomps, though they are very good (I prefer to use the KPA as mostly an amp/cab only which is why I focus on the tonal purity so much). I think I just saved myself some profiling time with these tests, because I will probably skip the clean profiling and continue using the actual amp for the critical clean recording as I described--though I plan to profile a few higher-gain amps. I wonder if a guy with a golden clean tone like Alan Holdsworth would mind that distortion... hmmm. ;)


    OK, I thought you were looking for a "all in one" solution, but I understand now. I do some composition in electroacoustic music, and until now I created some of my sounds from guitar -> pedals -> amplifier -> recording in Pro Tools, heavy heavy effects in Pro Tools, output in 96kHz 24 bits, and then spatialisation in 4 tracks for creating moving sound sources with a software that I wrote, which operates at 96kHz, 64bits. So I am very sensitive about the problem of aliasing, artefacts and tonal purity ! Yes, clean has to be clean. But I really consider using the Kemper for such situations, and I am also lookin for very pure profiles...


    Best regards.


    Jean-Jacques.

    Quote from Guitartone

    This thread seems to be fading away....hmmm, wonder why?


    Anyone hear any aliasing in this high gain clip?


    http://www.youtube.com/watch?v…s&feature=player_embedded

    Some good tone in that video, and it shows that the aliasing is largely masked depending on what you play, but there is a style of playing that can reveal it... and this isn't it. To me, really milking the notes in a high wailing lead is where it can reveal itself, not during straight riffing.


    A few days ago, several people chimed in on this thread with some good ideas on having a switchable option that could direct more dsp to the amp profile—I hope Kemper took note of that.


    There isn't a whole lot more to say about the aliasing that hasn't already been said, but this thread will not fade. We are kind of just waiting for Kemper to fix it, since they don't seem to want to chime in directly as to what they are planning.

    Quote from ckemper

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


    I wonder how Line 6 eliminated audible aliasing in their high-gain HD models—and with no fan. I had just bought a POD HD a few weeks before receiving my first KPA, and was impressed with what L6 had done in improving the aliasing that plagued all their previous PODs, so the KPA surprised me with its level of aliasing, though I must say that there has been an improvement since I reported it to them last April—they're going in the right direction. ^^

    Quote from miles

    Some good tone in that video, and it shows that the aliasing is largely masked depending on what you play, but there is a style of playing that can reveal it... and this isn't it. To me, really milking the notes in a high wailing lead is where it can reveal itself, not during straight riffing.


    A few days ago, several people chimed in on this thread with some good ideas on having a switchable option that could direct more dsp to the amp profile—I hope Kemper took note of that.


    There isn't a whole lot more to say about the aliasing that hasn't already been said, but this thread will not fade. We are kind of just waiting for Kemper to fix it, since they don't seem to want to chime in directly as to what they are planning.

    I agree this style of playing tends to mask it, i notice it especially on higher single note leads with alot of gain , simple test use a high gain profile (gain like 75 percent) , turn on the tube screamer effect block in front of the amp block play the high e string at the 20th fret or 22nd , bend it , pick it again bend , pick it again bend , i hear it then ...

    It would be interesting to know the number of users who have actually experienced this aliasing while playing through a KPA. I'm not denying that it exists (I can hear it in some of the clips posted) but the degree to which this is a problem might be an interesting datapoint.
    Probably because of the style of music I play and the rigs I use, I haven't experienced it so I guess if we were to keep a count
    -1
    Cheers,
    jayson