Display MoreMr Kemper himself posted the main EQ controls use these frequencies. If you are using the EQ post amp and turning up the TREBLE you will get a lot of the 2-2.5 kHz you are talking about.
For high gain you should always use the EQ as PRE AMP and then add a studio EQ as your first stomp after the amplifier to really dial in the EQ.
Since amplifier clipping adds a ton of high frequency signals, you can roll of some highs before the amplifier to get a smoother distortion. And then the STUDIO EQ is used to get you back where you want to be. Clipping a 100 Hz sine wave brings in 300Hz, 500Hz, 700Hz, etc out to infinity with gradual lowering volumes.
Every decent high gain sound I have ever looked at has this type of a frequency response. A flat line starting at 100 Hz and and ending around 5 kHz. Usually 10-15 dB drop between 100-5k.
So you should adjust the studio EQ to get something like this curve. The actual low end cuts pretty hard below 100 Hz. The slope above 5k gives you the airy and lively sound. Your IR will dictate that slope usually.
If you are EQ'ed to this slope and it stills sound really bad, I would start looking into a different IR. It is very important to keep your signal in phase. If your IR was not recorded in-phase you can get this curve but it will sound dark/weird/thin because the phase is not correct. So you get a signal at the right volume but it is out of phase with signals near it and they cancel each other out.
I always use a program called Goldwave. A stand alone app that does FFT while recording audio to see the frequency response. GW is a stand alone app. If you are using a DAW there are other options out there. It would be a good idea to have one of these type of apps running so you can see the EQ changes you are making. Personally, my ears are terrible so I need help from an app like this.
Another option is EQ'ing IRs to fit. If you purchase IRs they come as a WAVE file. These files can be loaded and edited in EQ software. Again, phase is important. Applying digital filters can cause phase errors just like real filter. Making small changes to the IR should not drastically change its overall shape.
You can also download ROOM EQ WIZARD and run sweeps on your Kemper with No amp blocks/effect/eq. This will give you a freq sweep of the IR that can be converted to an IR right in REW.
IRs are stored in WAVE file formats at 1024 or 2048 sample counts. So you will want to clip the new IRs to 2048 or something slightly larger.
To clip in time use 2048/Sample Rate to get an approx time.
2048 samples / 48000 samples per second = .04267 seconds. I would clip at say .043 or .044.
All good info - and thanks for posting those amp-stack EQ points, I'd seen them a while ago, and couldn't find them since!
The only thing I wouldn't entirely agree with is "For high gain you should always use the EQ as PRE AMP" - I have experimented with the amp-stack as "pre" and never managed to get good results - not saying it can't be effective, but personally what I find works best is studio EQ before amp (and I find this needs to be kept fairly subtle or it takes all the life out of my pickups - and often, if the problem is that profile is a bit dull, the treble booster does a better job) - then use amp-stack EQ post amp to make broad strokes (again needs to be kept subtle, or it starts to sound unnatural - with the exception of the bass knob, which seems to be fine with quite large adjustments) - then, post amp/cab, more surgical EQ-ing to get rid of any muddy or harsh freq's and boost any sweet spots (which I do in the DAW with ProQ, but Kemper studio EQ in X slot would also work) - this is where I set up hpf/lpf too, hpf usually between 80 and 110hz, lpf usually between 6 or 8k. Many ways to skin a crocodile tho - if we all end up with a killer tone, it's all good!