Question about Kemper

T

tomc3084

Experienced
Kemper says they do not use Impulse responses, correct? So how is it that the Kemper is able to load IRs? Sounds like BS to me. I mean how can a unit not use something but be able to load them? Weird......no?
 
The KPA profiles an amp+cab as one profile, so no IR is needed.

They also have a way of removing 'most' of the cab from the profile so that an IR can be used, or other cabs from profiles can be swapped.
It seems hokey but it works pretty good!
 
They also have a cool little utility called CabMaker that converts IR files into cabinets that can be used in the Kemper.
 
They do use IRs. They use 256 point IRs augmented with parametric EQ. This is easily demonstrated by examining the data structure of the profile and by measuring the device (or by using their IR converter which converts long IRs to 256 point IR plus EQ). What they say is "we use something more advanced" or something like that. By "more advanced" they mean they augment the IR with parametric EQ. However they must augment the IR with parametric EQ because the IR is too short to reproduce low frequencies accurately. The frequency resolution of an IR is proportional to its length: the longer the IR the better the resolution. To accurately reproduce a guitar cabinet requires at least 1000 points from my research. (Note: I'm using the term "parametric EQ" as a substitute for IIR filter since most people don't know what an IIR filter is.)

This technique has been around since the early days of modelers (I believe the Pod 2.0 was the first to do this). The impetus for this is that it uses much less processing power since the amount of processing power required is directly proportional to the length of the IR. A 256 point IR plus, for example, an 8-band EQ can be equivalent to a 512 point IR but uses less processing power. The downside is the phase response isn't the same but that is usually inaudible.

In their specific case the amplifier output frequency response and cabinet frequency response are combined into a single IR plus EQ since they aren't measured separately. See my MIMIC whitepaper for more information on frequency response, etc. You can make assumptions about the amplifier output frequency response in order to separate it from the cabinet response. In their case I believe they assume there is a 6 dB resonance at 125 Hz plus a 6 dB highshelf (incidentally this is the same power amp frequency response model that the Marshall JMP-1 used albeit using analog filters). For many amplifiers this is a reasonable approximation.

The Axe-Fx II IRs are 2048 sample (eight times the resolution) and don't require augmentation.
 
FractalAudio said:
They do use IRs. They use 256 point IRs augmented with parametric EQ. This is easily demonstrated by examining the data structure of the profile and by measuring the device (or by using their IR converter which converts long IRs to 256 point IR plus EQ). What they say is "we use something more advanced" or something like that. By "more advanced" they mean they augment the IR with parametric EQ. However they must augment the IR with parametric EQ because the IR is too short to reproduce low frequencies accurately. The frequency resolution of an IR is proportional to its length: the longer the IR the better the resolution. To accurately reproduce a guitar cabinet requires at least 1000 points from my research. (Note: I'm using the term "parametric EQ" as a substitute for IIR filter since most people don't know what an IIR filter is.)

This technique has been around since the early days of modelers (I believe the Pod 2.0 was the first to do this). The impetus for this is that it uses much less processing power since the amount of processing power required is directly proportional to the length of the IR. A 256 point IR plus, for example, an 8-band EQ can be equivalent to a 512 point IR but uses less processing power. The downside is the phase response isn't the same but that is usually inaudible.

In their specific case the amplifier output frequency response and cabinet frequency response are combined into a single IR plus EQ since they aren't measured separately. See my MIMIC whitepaper for more information on frequency response, etc. You can make assumptions about the amplifier output frequency response in order to separate it from the cabinet response. In their case I believe they assume there is a 6 dB resonance at 125 Hz plus a 6 dB highshelf (incidentally this is the same power amp frequency response model that the Marshall JMP-1 used albeit using analog filters). For many amplifiers this is a reasonable approximation.

The Axe-Fx II IRs are 2048 sample (eight times the resolution) and don't require augmentation.
Click to expand...

Wow, great explanation. I had a feeling this is what was going on. I wonder why with this method some people favor the Kemper tones to Axe FX. For example, you will see in many threads people saying that the 'core amp tones' are better in the Kemper than the Axe. I am going to go out on a limb and guess most people that say that either A) Have never used an Axe FX or B) It is all in their heads. It is so funny to me when users or the Kemper correct people when they refer to the Kemper as a modeler, lol. Most times they say , Kemper doesn't user Impulse responses like all other modelers, it uses profiles and isn't a modeler. It is also funny on the Kemper website where they say the Kemper is able to recreate certain high gain sounds where impulse responses fail miserably. So glad I decided on the Axe FX II over the Kemper. I will be honest, after reading all the threads where people say the Kemper is better than the Axe FX at pure amp tones, I have been GASing a little bit for a Kemper. Now after reading Cliff's post, I have no desire whatsoever to get one. Seems like the Axe does everything the Kemper does and more. Thanks again for that post Cliff.
 
tomc3084 said:
I had a feeling this is what was going on.
Click to expand...

Yeah, me too!
laughing.gif
 
tomc3084 said:
Wow, great explanation. I had a feeling this is what was going on. I wonder why with this method some people favor the Kemper tones to Axe FX. For example, you will see in many threads people saying that the 'core amp tones' are better in the Kemper than the Axe. I am going to go out on a limb and guess most people that say that either A) Have never used an Axe FX or B) It is all in their heads. It is so funny to me when users or the Kemper correct people when they refer to the Kemper as a modeler, lol. Most times they say , Kemper doesn't user Impulse responses like all other modelers, it uses profiles and isn't a modeler. It is also funny on the Kemper website where they say the Kemper is able to recreate certain high gain sounds where impulse responses fail miserably. So glad I decided on the Axe FX II over the Kemper. I will be honest, after reading all the threads where people say the Kemper is better than the Axe FX at pure amp tones, I have been GASing a little bit for a Kemper. Now after reading Cliff's post, I have no desire whatsoever to get one. Seems like the Axe does everything the Kemper does and more. Thanks again for that post Cliff.
Click to expand...

It also could be that the Axe Fx is so close now, that the actual amps are what they don't like, not the modeling of them.
 
I also wonder why he says it took him several years to come up with the profiling if it is something that has been around for awhile. Sounds like a bunch of marketing hype to me. Seems like they took a old method and had some great marketing.
 
The core amp tones in V10 are superior IMO. Our modeling captures both preamp and power amp distortion. Their modeling lumps it all into one and attempts to fit a (k-x)/(k + x) waveshaper using difference minimization. See the papers by Klippel for more information on model fitting. V10 uses the same technique but fits true triode models to the preamp measurements and true push-pull tetrode/pentode models to the power amp measurements. If you listen to their models you'll never hear any crossover distortion because they don't model it. If you don't like crossover distortion then this is irrelevant, however many modern, aggressive amp designs exploit crossover distortion. This is probably why the Axe-Fx II has a better reputation for high-gain tones.
 
tomc3084 said:
I also wonder why he says it took him several years to come up with the profiling if it is something that has been around for awhile. Sounds like a bunch of marketing hype to me. Seems like they took a old method and had some great marketing.
Click to expand...

A typical product design cycle takes about three years.

Profiling is a unique application of distortion model matching (see Klippel et. al) and EQ Matching (i.e. ozone). They have also developed a unique method of measuring input frequency response and dynamic response.

It is a fine product and produces good results. Whether those results are superior or inferior to other products is a matter of opinion.
 
tomc3084 said:
Wow, great explanation. I had a feeling this is what was going on. I wonder why with this method some people favor the Kemper tones to Axe FX. For example, you will see in many threads people saying that the 'core amp tones' are better in the Kemper than the Axe. I am going to go out on a limb and guess most people that say that either A) Have never used an Axe FX or B) It is all in their heads. It is so funny to me when users or the Kemper correct people when they refer to the Kemper as a modeler, lol. Most times they say , Kemper doesn't user Impulse responses like all other modelers, it uses profiles and isn't a modeler. It is also funny on the Kemper website where they say the Kemper is able to recreate certain high gain sounds where impulse responses fail miserably. So glad I decided on the Axe FX II over the Kemper. I will be honest, after reading all the threads where people say the Kemper is better than the Axe FX at pure amp tones, I have been GASing a little bit for a Kemper. Now after reading Cliff's post, I have no desire whatsoever to get one. Seems like the Axe does everything the Kemper does and more. Thanks again for that post Cliff.
Click to expand...

To me, this is a good example of ears over eyes. Regardless of math and algebraic formulas, the Kemper sounds phenomenal. Whatever is happening in terms of IR's in the KPA, it certainly hasn't had a negative impact on the tone.

And this is not a knock on the Axe II, because we all know that it sounds phenomenal too. But don't let others influence your decision simply based on numbers and theories. Give them both a try if you can and keep whichever suits you best. I have both in my rack (along with an Eleven Rack) and find things I love about each. The Kemper may have flaws, but great tone is not one of them.
 
FractalAudio said:
The core amp tones in V10 are superior IMO. Our modeling captures both preamp and power amp distortion. Their modeling lumps it all into one and attempts to fit a (k-x)/(k + x) waveshaper using difference minimization. See the papers by Klippel for more information on model fitting. V10 uses the same technique but fits true triode models to the preamp measurements and true push-pull tetrode/pentode models to the power amp measurements. If you listen to their models you'll never hear any crossover distortion because they don't model it. If you don't like crossover distortion then this is irrelevant, however many modern, aggressive amp designs exploit crossover distortion. This is probably why the Axe-Fx II has a better reputation for high-gain tones.
Click to expand...

I wish I could like this statement more than once!
 
Seems to me there are two issues.

Firstly, a debate centred around the comparison of different technical aspects of modeling/profiling amp/cab tones which I don't profess to understand.

Secondly, a comparison of the tones delivered by the two units. I think this is more relevant, regardless of how the units work or the technology employed.

For me, it's ALL about how it sounds, I really could care less about the technology. My unit of choice is the AFX which gives me everything I need and then some. I would be more than happy to get a Kemper at some point in the future to go with my AFX and stick them both in my rack alongside my Pod X3 pro, I don't get hung up on gear snobbery.
 
I have both & they are both really great. Both also have room for improvement for sure.

The tech speak is fine and all, but really meaningless at the end of the day.

There are many Axe-II users that would prefer the Kemper for some things if they owned one, and the same can be said for Kemper owners.

Those of us who own both, plus also own some fine tube amps, can't be fooled by the hype or negative fanboi rants.......
 
Webb said:
To me, this is a good example of ears over eyes. Regardless of math and algebraic formulas, the Kemper sounds phenomenal. Whatever is happening in terms of IR's in the KPA, it certainly hasn't had a negative impact on the tone.

And this is not a knock on the Axe II, because we all know that it sounds phenomenal too. But don't let others influence your decision simply based on numbers and theories. Give them both a try if you can and keep whichever suits you best. I have both in my rack (along with an Eleven Rack) and find things I love about each. The Kemper may have flaws, but great tone is not one of them.
Click to expand...

Yeah, but thats like saying that an Mp3 conversion is just as good as a high quality wav. Yes at first listen the artifacts aren't noticable, but when you start combining multiple tracks, like you would with multiple guitars in a mix, the result becomes more noticeable. I dont disagree that the Kemper sounds good, but as far as flexibility and all around features, AFX still gets the win. Not to mention that the potential for the axe to get even better is already "built" into the unit because of the superior hardware and IR features, whereas the Kemper seems to already be making up for inadequacies such as the discussed IR sample restrictions.
 
I'm pretty sure that I could get basic sounds I would like out of either unit... but the Axe FX II is also a kick ass effects processor, and that totally seals the deal for me. Still want an Access Virus TI though...
 
That's the longest post I've ever seen by Cliff. Pretty lucid if even I can understand

:encouragement:
 
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FractalAudio said:
They do use IRs. They use 256 point IRs augmented with parametric EQ. This is easily demonstrated by examining the data structure of the profile and by measuring the device (or by using their IR converter which converts long IRs to 256 point IR plus EQ). What they say is "we use something more advanced" or something like that. By "more advanced" they mean they augment the IR with parametric EQ. However they must augment the IR with parametric EQ because the IR is too short to reproduce low frequencies accurately. The frequency resolution of an IR is proportional to its length: the longer the IR the better the resolution. To accurately reproduce a guitar cabinet requires at least 1000 points from my research. (Note: I'm using the term "parametric EQ" as a substitute for IIR filter since most people don't know what an IIR filter is.)
Click to expand...
I don't have any engineering knowledge, but I'm candidly curious about one thing : a profile, which contains the complete rig settings including the effects and the IR, has a file size of only 4 KB. A standard 1024 points IR is 7 KB. Question : is there a way to "compress" an IR, like a .mp3 is to a .wav ? IRs are audio files, after all...
Btw, Christoph Kemper answered to Cliff's post here : KPA, IRs and math mumbojumbo - Kemper Profiler related discussions - Kemper Amps Forum
The KPA does sound very good and I wouldn't mind owning one, specially for clean and crunch sounds... It won't meet my needs for hi gain sounds and effects though, and I'd rather save for a high end guitar
 
Yes for the models I know that, although I read that it's one model for clean and one for distortion. But for the IR? Just curious, how can a 4 KB can contains that many information ?
 
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