Confused by high and low pass functions. please help!

what are you high/low pass settings on the output stage?

Low pass is high frequencies. High pass is low frequencies. So dang confusing. Usually, the only other frequency you want to EQ is somewhere in the mids. Boost those signals higher with an EQ, from the 250k, - 1k range, to see if that frequency annoys you more - then you know what frequency it is and you can cut it down.

In all the HPF / LPF filters I've seen, they're always a ramp rather than a hard line drawn perpendicular at the cutoff frequency. Because of this, your HPF doesn't kill 100% of the signal from 0 to 80. Rather, it attenuates by x dbs, with x depending on where the frequency hits the ramp.

Picture the right hand portion of the letter V, with the lower point being 0 and the upper being 80. The bottom of the V is off, the top is on. Now imagine 40 being halfway between the two from left to right, and you can see that it doesn't get turned all the way off, it's only turned down partially.

This is a terribly clumsy layman's explanation and I'm sure the knowledgeable guys can offer more clarity, but hopefully this helps you understand why an HPF at 80 doesn't kill 100% of the signal below 80.

Just so we're all talking about the same thing, this is from the Kemper Manual

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Output Filters
Low Cut and High Cut filters are available. These will affect all outputs.

Kemper Manuals and Quick Start guides
Search for Output Filters

I didn't see a reference to low pass and high pass filters. However, there are frequent mentions of low cut filters throughout the Kemper manual.

Here's an interest quote (note - the original was in German and this is translated by the Google Chrome browser)

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I am pleased to be able to write here in German again.

I have a very mixed relationship with cut filters, which are required individually for each output.

Cut filters should only be used for artistic processing of sounds

Oxer to suppress background noises that do not belong to the useful signal, such as the low-cut filter on mixing consoles.

A guitar signal that is too bass, however, has no background noise.

However, cut filters should not be used for frequency response correction. Too much bass should be fought with less bass, but not with clipping the bass.

However, it is legitimate and often practice to cut off the bass portion of the amp to make room for the bass guitar and bass drum. This is more artistic than correction as it has to do with the song and the arrangement.

A responsible and self-confident musician should make these artistic settings during rehearsals - possibly even per rig - and coordinate them with the band.

An FOH who says "I'll take it out myself" doesn't seem to have too much trust in the musician, and maybe he doesn't have enough experience with digital guitar amps. However, an FOH should be happy when the band offers good signals. However, he can give tips on how to correct them during the sound check.

Frequency ranges that are cut off at the monitor output, but not at the main output, make the signals very uneven and decouple the guitarist's playing style from the sound dynamics at the FOH. That can only have disadvantages, I can't see possible advantages, unless you are afraid of the evil FOH

The monitor EQ is currently not really made for influencing rumbling noises. We could try, however, to lower the EQ bass control.

At the moment it is 120 Hz, but it is steep (12 dB / oct). 80 Hz might be better.

CK

Source: Low-cut High-cut im output menue

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And this give some insight into how the cut filters behave.

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The High Cut frequency indicates the cutoff point of the lowpass filter.

Depending on the filter type, the energy in the frequency band one octave above this cutoff point is attenuated by 6dB, 12dB, or 24dB - to name just the most common types.

Setting the High Cut at a frequency does not mean that everything above this frequency is removed.

From DonPeterson
Source: EQ Low Pass Filter / High frequencies Cut

Quote from Daviebutt76

Surely it'd make more sense for it to be set to only create 'guitar-like' frequencies in the first place!?! I'm guessing that this is where somebody is going to tell me that the 'magic' in a guitar amps sound lives in a little bit of those fizzy and / or boomy frequencies being added?

"Guitar-like" frequencies is a bit ambiguous and thus difficult to define even in the most limited ways. In standard tuning on a six string, from the open low E to highest fretted E note might be considered the complete range of frequencies. However, there are also seven string guitars, dropped tunings, etc. so to those guys, it's a different range of notes.

Then there's all that magic stuff. Even with a standard six string, if you stick a mic in front of a tube amp / speaker cab, then record and analyze the results, you'll find a much wider range of frequencies than just the notes on the guitar. And what you get will vary widely with each change in amp, cabinet, mic, and mic placement. And that's before you start twisting knobs on the amp head. A guitar tone is a complex creature.

Quote from Daviebutt76

What i don't understand, still, it why on earth the Kemper allows frequencies, which should never be present in guitar tone, to be present?

Then there's the physical reality of it all. You plugged a guitar into an amp. If the frequencies are there, then they were generated by your guitar / amp / speaker cab and thus are, by definition, "guitar-like" frequencies. It's not like they were snuck into your speaker cabinet and duct taped to the back of the speaker cone by elves in the night.

Obviously a lot of those frequencies don't work for you, hence the desire to eliminate them, rogue elves notwithstanding. And that's absolutely fine. A guitar tone is a very personal thing, so whatever you want to hear is the correct thing for you to hear. That said, if Kemper tried to arbitrarily eliminate frequencies that would normally be generated by a given amp / cab combination based on your recommendations, they would be forcing everyone else to use the same kind of tone as you. I suspect that would cause riots in the streets. Or at least a mass migration to another guitar amp.

Rather than being unhappy with physical reality, I think you'll get the most enjoyment by focusing on how to achieve the tone you're looking for. If it were me, at the point where I found myself having to do heavy tweaking to get my sound, I would instead be moving on to other profiles.

Also, since you're new to the Kemper, I'll mention a mistake I made when I first got mine that almost resulted in my boxing it up and sending it back. For reference, I'm a classic rock guy. So, the first thing I did was browse through all the free profiles on Rig Exchange looking at Marshalls. I was absolutely stunned by how bad they all sounded. And not in a subtle way. Eventually I realized that I was making assumptions. I saw "Marshall" and assumed it would be dialed in like I would dial in a Marshall. However, that same head can play Earth, Wind and Fire, Bonnie Raitt, Bad Company, or New Age Post Apocalyptic Lunar Metal. Same amp, huge difference in tones. What a metal guy thinks is awesome would get me kicked out of a Bad Company tribute band, and my settings would get me laughed off of a metal stage.

Remember, a profile is not, "Here's a Marshall JCM 800, do as you will to it." It's a single moment in time after someone selected a speaker cab, dialed in a tone, chose a microphone, placed it to taste and did the profile. If they dialed in the tone for Earth, Wind and Fire, you ain't gonna get good metal no matter how many pedals and EQ settings you throw at it.

A profile is a snapshot, not an amplifier.

So, if you're finding frequencies that don't work for you, instead of trying to polish a turd (sorry, I'm from the deep south in the US), move on to other profiles and find the source material that's closest to what you want. I actually have a wide selection of profiles that absolutely nail my tone with zero tweaking. It's all about finding profiles from people who are into the same genre as you, and do it well.

I hope this helps you get a feel for the wheel. The Kemper will definitely get you where you want to go, you just have to know how to drive it.

To be sure, we're getting into areas where I don't really know what I'm talking about (and believe me, you don't have to travel very far to hit that border).

That said, because I didn't know, I just looked up the frequency response of a Celestion Greenback. The chart linked below goes down to 20 hz and as high as 20k. So, the speakers can reproduce quite a bit, certainly in excess of your preferred 80 / 5k filters.

https://celestion.com/product/16/g12m_greenback/

At a certain point you go beyond the boundaries of human hearing, but I think perception is still colored by those ranges because air is still being moved whether the ears interpret it or not. In the lower ranges it can translate to things like the thump in the gut that you feel when chugging, etc.

I honestly don't understand the field of acoustics enough to speak intelligently on the matter. Then again, I don't understand girls, either, so I've learned to live with my limitations.