Posts by Laimon

  • FCB1010 or GORDIUS LG2 using one single cable only

    AWESOME! Great job Xavier, I love my LG2 8)

  • The Aliasing Problem

    Quote from Per


    Actually it was fixed back then on the next firmware update after he posted that (1.6.1 I believe), so at that time they did make the algorithm more intensive to solve the aliasing issue and now the CPU cycles are being used for this rather than other effects right now, so the scope for further improvement is probably non-existent at this point :/


    Are you 100% sure the aliasing effects you're hearing aren't pickup warble and frequency interference? A real amp will give the same results in this case.

    Hi Per, yes, indeed I read these lines in a thread about aliasing back then, before 1.6.1 was released.
    I am 100% sure, I profiled my amp and compared the profile with my amp: in the first case there were signs of aliasing, in the second case none.
    Also, this has been acknowledged by kemper support: I opened a ticket, they could reproduce the problem, solved it and they're gonna include the fix in the next release.

  • AxeFx 2 profiles

    Quote from Chgros

    Hey thanks !


    Any chance to have some Preamp only profiles of amps to test with the powered rack + guitar cab ( just ordered my powered kpa a few days ago :) , sold my axe II 2 weeks ago) ?

    You can remove the cab sims without a problem: the kemper does not need to have information about the original cab, it uses an heuristic to "guess" how the rig would have sounded like without cab and mic and I must say that works pretty well.

  • The Aliasing Problem

    Hi OneEng, what you say is technically correct, but I think you might be assuming certain things that don't hold, or missing some perspective on the problem (the thread is quite long now, so it's easy to have missed bits here and there). Let me comment on your statements to clarify the issue.

    Quote from OneEng1

    While it is true that a guitar (and certainly a guitar and a stomp box) can generate frequencies that are quite high, most guitar cabs can't reproduce the frequencies. Here is the spec sheet on the ever popular vintage 30: http://celestion.com/product/1/vintage_30/


    Quote from OneEng1

    You aren't going to get much over 15KHz out of this speaker no matter what you put into it.

    The aliasing we're discussing here is mostly apparent when deactivating the cab sims and going to a guitar amp. Clearly a preamp output has a much more substantial high-frequency content than a cab output. However, mind that on several rigs one can hear it (much more subtle, of course) also with cab sims on going through a FRFR speaker.

    Quote from OneEng1

    As for aliasing, it isn't caused by the A/D or D/A in the real world. All modern A/D converters are capable of sampling at very high frequencies (>192Khz). If you study electrical engineering (I am an EE myself), you learn that you can digitize a signal by sampling it at discrete points, processing it into the frequency domain, then changing it back into the time domain and feeding it into a Digital to Analog converter (D/A) to output the voltage EXACTLY like it was before you digitized it ....... as long as you sample 2 times as fast as the highest frequency you wish to reproduce.

    Thanks, I know what aliasing is :P
    You can surely sample very fast, but then you'd also need to process way more data, and that requires more computing power. You say:

    Quote from OneEng1

    I doubt that the Kemper is processing bound.

    but that seems indeed to be the case: Cristoph Kemper said some time ago that fixing the aliasing would be no problem, but would require to speed up the algorithms, and he was hoping to save the processing power for future features. So the computing power is indeed to be treasured ;)

    Quote from OneEng1

    So, sampling at 44Khz would give an effective reproduced frequency ceiling of 22Khz ..... which is higher than most humans can ever hear even at birth ..... and much higher than any guitar cab I have ever heard of being capable of reproducing.

    Uhm, the fact that humans can hear a frequency is irrelevant: if a mic can catch it, or the Kemper internal processing produces it, then that will generate aliasing, and humans will hear that one ;)

    Quote from OneEng1

    Now what DOES cause aliasing in the real world is down sampling in order to reduce processing, or mistakes in the DSP signal paths which result in a time alignment issue that results in something that sounds like aliasing.

    That might be. Data overflow then?

    Quote from OneEng1

    My educated engineering guess is that what we are hearing in the Kemper is the latter .... and it can be easily fixed by modifying the DSP code to better align things internally.

    They could tell us, they already fixed it, and it's coming in the next firmware release :)

  • Using Kemper or Axe Fx Live

    I have had both and never used any live, for whatever reason. Anyway, I can only imagine that dealing with it live is as difficult as in a room tweaking for getting the sound you want: with the Axe it's a pain, with the Kemper a breeze. I don't think I could dare delve in the Axe FX parameters while live, it's just too long and convoluted, but fixing the Kemper is as easy as turning knobs on a real amp (exactly because they made it to resemble the classical amp layout :P )

  • The Aliasing Problem

    No, the aliasing is purely a conversion artifact. Things can go wrong in the processing (fictitious example: a whammy pedal could raise a frequency to the point of not being representable with the used data types and lead thus to overflowing), but aliasing really just pertains to the conversion phases. Moreover, it is way more likely to occur in the DA conversion than in the AD one: your guitar is very unlikely to spit out > 22kHz, the lead channel of diezel amp with a tube screamer in front of it has much higher chances ;)

  • Which features would you like to be added next?

    Quote from kamin21

    It would be awesome to use the KPA integrated in DAWs as a VST.
    For example to add more gain in some bars or change cab-parameters over time.
    Of course you can do it already but it's much harder to achieve.

    Well, first thing the kemper should be enabled to work as sound card, so send audio (and midi - tell you now why) via USB cable.
    Then, a VST can also be made by a 3rd party, say a user with proper coding knowledge, that simply controls the Kemper via midi. That would take some load off the kemper developers, which I am sure are already working 110% ;)

  • The Aliasing Problem

    Quote from Michael_dk

    Stupid question: Could the aliasing come from processing AFTER the conversion?

    Well, if you mean after analog (guitar) to digital, yes, the aliasing happens in the later - opposite - conversion, that is from digital to analog. The "harmful" frequencies (i.e. too high harmonics) are added in the digital signal processing by the profiles (high gain ones).
    If you mean instead after digital to analog conversion, no, that is simply not possible. Aliasing does not exist in the analog world ;)

  • We have the Cab Maker - then why not the Preamp Maker?

    Yeah. What I find is that "preamp" profiles and "full rig" profiles are indistinguishable to the kemper, and depending on your setup you can use only one set of profiles or the other.
    But, if we can separate the cab from the rest of the stack, can't we also just say that a profile is a "preamp profile" and then add it whatever cab profile we like?

  • Mix on Wah?

    Quote from andyg_prs

    I was using the wah on my lead profile today which is high gain and a fair bit of delay. I noticed that I was getting some really over the top warbling that I couldn't control with the wah pedal....pretty much out of control.....I tried playing with the mix, that was set to 100% and progressively reduced it to 0% and the wah is much more like a 'normal' pedal.


    What does the mix do? If it is the balance of dry to wet sound then on 0% the wah shouldn't function at all?


    Thanks,
    Andy

    That's unclear to me as well, actually. I just checked the manual and found nothing regarding the mix.

  • The Aliasing Problem

    Quote from artembankin

    Guys , you can try to reamp a simple rising test tone an hear a strong aliasing gurgling with all of kemper profiles...with latest fw...
    aliasing not destroyed in 1.6.1 fw , it just became unaudible...with most cases of real guitar sound


    But, some VST amp plug-ins ,with enabled 16x oversampling - do much more less aliasing than kemper on test tones...
    and this fact slightly frightens me...low processor power , imperfect algorithms ?

    Well, aliasing cannot be removed entirely, you know. It appears whenever you're trying to convert from digital to analog a frequency that is higher than half the sampling rate; the conversion cannot distinguish, given the insufficient amount of samples, the intended frequency from one much lower and in the supported frequency range. You can always feed the kemper a signal that is higher than half its sampling rate.
    This is to say that "just making it unaudible" is far from a bad solution! The common solution (the one that has been applied, as far as I know) is to sample more, simply. But that requires algorithms to go faster.
    Mind also that the remaining aliasing from 1.6.1 firmware on, it's not only "softer" to the end of being inaudible: it's really a smaller range of frequencies that are being erroneously converted, because by raising the sampling rate only very very high harmonics are exceeding the supported range, and these harmonics wouldn't be very strong in the first place.
    The other solution, that I would personally use but I guess there is some reason why it is not used, would be applying a lowpass filter before conversion. Such a solution would be even final (well, provided the input itself wasn't higher than supported). But maybe here someone can chime in and explain me why it wouldn't be doable.

  • The Aliasing Problem

    Quote from mdeeRocks

    BTW - I have noticed similar sounding problem on a couple of profiles - I am not sure if it's aliasing or not, but it's not very pleasant. Let's see if new firmware alleviates it.

    Yes, they acknowledged the problem and told me that developers already "patched" it for the next firmware release (hopefully that will come soon)

  • Gordius Little Giant - aka the most awesome midi board

    Hi Tocry,


    to be honest I still haven't taken the time to plug in the Gordius and the Kemper together, so I can't really answer your questions yet. I know Xavier implemented support for the kemper, but I don't know to which extent.
    Regarding the connections in and out of the kemper, well you can use two midi cables of course, or go for some solution like described here:


    Gordius Little Giant - Two way communication & power in one cable


    I think some day I'll give it a shot myself!
    Cheers

  • Best DI?

    Quote from londonjeepster

    is there a particular reason you want to make DI profiles instead of "full" profiles? by taking your speaker out of the profile you are going to end up with a basic amp sound which is no different from thousands of others.
    its really best to use a mic if you want an accurate profile of the full sound of your combo.

    I don't see the problem with that, and in fact, it seems like a purer approach to getting the exact sound of your amps, when you plan to use them anyway with a non-FRFR (i.e., guitar) cabinet. When you deactivate the cab sims from a full rig the Kemper is only guessing what the "preamp portion" sounded like (a good guess, sure, but still)

  • Recursive search in subfolders

    Quote from HELL-G

    Search in Location 'All Rigs'. The result will show where the found items are located. Activate the respective column with right click => Located In.

    Well, yeah, but there you get all results. Say I have locally a folder The Amp Factory, within which I have several different amp collection, and I'd like to search for all clean sounds. I just think this would be fairly useful.

  • Recursive search in subfolders

    Maybe this has been asked already, but I'll ask again...notice that I actually didn't check if there is already an option for it and now I am not at home to try, in that case just discard my question.
    So, I was trying to organize my profiles in the Rigmanager, with a sensible nested structure that would be easy for me to locate things, but then trying the search I notice that it doesn't go recursively over subfolders, that is: if I have folder A and folder B, B being son (or descendant) of A, and A selected, the search returns only profiles contained strictly in A, but not in B. To me this is quite counterintuitive, has anyone requested this feature before?

  • kemper profiler users, what's your "profile" ;-)

    Quote from lightbox


    Yes, it is. And you'll be pleasantly surprised when you feel playing the Profiler and notice how it (the rigs) responds to your playing. So basically you heard the great sound already and the added response to your playing will make you smile like :D everytime you use it.

    I don't know, then I must be doing something wrong myself cause I really can't get along with playing with headphones.

    Quote from denishermans

    Indeed the response is often "a problem" with modelling when compared to tube amps.
    I'm getting very curious now :P

    Well, I understand why you worry (I also did), but you really shouldn't: the reason why the Kemper is becoming so popular is that really sounds and feel like the real thing. I'm not just saying "it's better than previous modelers", you will really feel immediately at home ;)

  • The Aliasing Problem

    Quote from OneEng1

    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