Need help in understanding and using the Studio Equalizer as a post-EQ to tame some harsh frequencies in my FRFR.

    Hello fellow Kemperites,


    I have learned that, when it comes to EQs, I am completely clueless...and probably a bit dangerous. :thumbup:
    Discovering that I have no idea how to best employ EQ towards a given purpose, has been quite the humbling experience.


    In my defense (somewhat), the KPA user manuals provide little guidance. The Reference Manual doesn't even explain terminology, nor list the parameters that are available in the "Studio Equalizer". The wiKPA site has a bit more information...but can often times be confusing and frustrating, especially when the FAQ dialogue(s) use terminology that doesn't even correspond to the effect's list of parameters. Again, using the "Studio Equalizer" as an example, here is the wiKPA page link:


    http://www.wikpa.org/Studio_Equalizer


    At the beginning of the article, the following parameters are listed:



    This is all well and good...but but there is no detailed explanation as to what these parameters mean, nor what they do. Now, obviously I understand "Frequency". And I can suss out that the "Gain" parameter is the level of boost or cut (I assume) of that frequency. But what is the inter-relationship between them? In one of the dialogue boxes, it is explained that the Low Gain / Low Frequency and High Gain / High Frequency are "shelving" filters. What exactly does that mean? What do these do?


    Continuing on...I understand that there are two separate parametric bands, Mid 1 and Mid 2. However, nowhere is there an explanation of what the "Q" parameter does, or how best to adjust this.


    What becomes a bit frustrating, is that some of the contributors start using different terms for what I assume correspond to the parameters listed above. For example, in the Christophe Kemper dialogue box, he writes the following:


    Quote

    The shelving filters gain goes down to -18 dB. If you bring the lowshelf this way down, you have virtually created a lowcut or highpass filter (which is the same as you know). The only difference is that you still have the "cutout" signals sounding at -18 dB, which is very low.
    I am sure that you want to attenuate the boomy frequencies, but not totally kill them, so you will probably end up in attenuating them by less than 18 dB.
    Lowpass and Highpass filters are used for killing frequency components in the signal that are absolutely not wanted. They can be considered as Shelving filters with gain at minus infinity. If those unwanted signals are low anyway, shelving and cutting filters don't make a big difference.
    But Lowpass and Highpass filters are great for artistically modifying a signal, since they work pretty radical.


    Sounds great...but what are these "shelving filters"? What is the "lowcut" and "highpass" filters? They are not designated terms in the list of tweakable parameters? Now, I am not completely dense...I presume that this terminology has something to do with the first four parameters (Low Gain / Low Frequency and High Gain / High Frequency). Am I correct? If I am, I still am unclear as to how to use them for best effect.


    In Don Peterson's dialogue box, he provides some recommended settings. But then he goes on to write the following:


    Quote

    Also, if you want to remove the very low end, I recommend placing a EQ or Highpass Filter with Peak 0.0 (!) and Manual at around 0.5 before the amp, so that the profile doesn't have to deal with these frequencies to begin with.


    How does this apply to the Studio Equalizer. I see no parameter called "Highpass Filter". I don't know what "Peak 0.0 (!)" means. And there certainly isn't a parameter called "Manual" in the Studio Equalizer.


    By this point, I am pulling my hair out in frustration, while simultaneously kicking my own damn self for having never learned about Parametric EQs. :P:D


    So, I am hoping anyone could shed some light on the questions and points I raise, above, specifically in regards to the Studio Equalizer Effect.


    I realize this is getting long-winded, but I have now actually come to my primary reason for asking for help (although I would still appreciate answers to above).


    Still with me....? Good. Here is the second part of my plea for help...


    I remember watching a YouTube video a few years ago, in which someone was demonstrating one of the digital modelers (not a KPA or Axe-FX). Specifically, he was showing how to use a parametric EQ to selectively pinpoint and mitigate/suppress any harsh and undesirable frequencies. I remember that part of the explanation involved "sweeping" the frequencies in order to find the offending frequency, and then dialing it out (reducing the Gain/Level ??). I can't find this video again. But in any event, can you folks explain how I might go about doing this with the KPA's Studio Equalizer, which I understand is a parametric EQ. I have noticed some harshness and buzz on some tailing distorted notes...and they sound like they are in the higher frequencies. I don't get this issue when I connect my powered KPA to a physical/traditional guitar cabinet. The issue only comes up when I am connected through my passive FRFR monitor. I assume the traditional guitar cabinet is naturally dampening these frequencies...while the FRFR monitor is reproducing the full dynamic signal, warts and all. So, I am hoping to find and dial these "offensive" frequencies out, using the "sweeping" method with the Studio Equalizer.


    I would appreciate any and all advice and instructions on how to go about this. Assume I know absolutely nothing about parametric EQs (a safe assumption, by the way).


    Thanks in advance, mates!

    The answer to your question about sweeping the frequencies to get rid of harshness is down at the ***s.


    Filter is a more technical way of saying EQ. You're putting a filter on it so only the frequencies you want come through. Filters come in three basic types:


    Band: You pick a center frequency, a width (Q, where higher = narrower. A Q of 1.4 is one octave), and the amount of boost or cut. This makes a bell shaped curve, if you were to look at it on a graph.
    Shelf: You still pick a center frequency, width, and amount of boost/cut, but this time it affects EVERYTHING above or below (high or low shelf) your frequency. In this case, the width determines how sharply the edge of the shelf curves.
    Pass/Cut: These are opposite names for the same thing - a high pass is a low cut, and vice versa. Similar to a shelf, but rather than adjusting the volume you're simply throwing out everything above or below the center frequency, with Q once again determining the steepness. High pass means that higher frequencies are passing through, so you're getting rid off the lower stuff, etc.


    It's important to note that, since sound and filtering don't behave perfectly, all of these WILL affect frequencies outside of the range you specified. For a high-pass, say, rather than having a sharp cut-off at your frequency, there will a curve starting slightly higher that becomes much steeper as it drops below your center. Similarly, a high shelf boost with a low Q would still be pulling up frequencies below your center, but the center is where it really starts to work.


    Now, as far as the Kemper's Studio Equalizer goes:


    Low and High are shelves, and in this case their Q is non-adjustable. What Christoph says about -18db and high pass filters simply means that, with a higher Q, turning a shelf down 18db is more-or-less the same as simply high-passing at the same frequency. The lower frequencies are still present, but you can basically ignore them. If they were still a problem, you could always add a second Studio Equalizer with the same shelf to turn them down even more.


    Mid1 and Mid2 are bands, as I described above, with a maximum boost/cut of (I think) 12db. Maybe 18, I forget. You would use these to emphasize specific parts of your tone, or get rid of parts that you don't like. For instance, a lot of the really quacky/honky pick attack lives somewhere around 1-2kHz, so a small, narrow boost there might sound similar to a Tube Screamer.


    ***For high-gain stuff, it's common to have a few ugly, whistly-sounding frequencies in the 2-6kHz range, so one popular solution is to take an EQ band, make it really narrow and crank the boost all the way up, then sweep the frequency knob up and down while playing to see if you can find any trouble spots - trust me, you'll notice them. It's almost like microphone feedback. Once you find one, turn the level back to zero and then start turning it down a bit at a time (preferably flipping the EQ on and off to hear the difference) until you're happy.


    The Kemper does also have a high/low-pass filter, just not with the other EQs in the list - they're back at the beginning under the Wah effects, since you can use them with a pedal to sweep the frequency of the filter up and down. You just have to load up Wah High Pass or Wah Low Pass and set the Pedal Mode to "Off" to get a stationary filter that you can control with the knobs on the KPA. In this case, Manual adjusts your frequency and Peak adjusts your Q.


    (Incidentally, a wah pedal is pretty much just a band-pass filter - that is, both a high- and low-pass together, so you're keeping just a narrow band of frequencies - with the pedal controlling the center frequency)


    Now, as for the buzzing on your note tails... may I ask what power amp and FR speaker you're using? I had a similar issue with my Crate Powerblock and Xitone wedge, and it turned out to be a combination of a damaged tweeter and the Powerblock starting to crap out. Anything that produced a big "oomph", like a palm mute on the low E, would have a bit of a crackling buzz on the tail.

    Quote from Lokasenna

    The answer to your question about sweeping the frequencies to get rid of harshness is down at the ***s.


    Sweet Fancy Moses!!


    Thank you so much, Lokassena!!



    What a fantastic, detailed write-up and explanation. This should ABSOLUTELY go up on the wiKPA site. Well done, sir. :thumbup:


    Quick question on this part:


    Quote

    For high-gain stuff, it's common to have a few ugly, whistly-sounding frequencies in the 2-6kHz range, so one popular solution is to take an EQ band, make it really narrow and crank the boost all the way up, then sweep the frequency knob up and down while playing to see if you can find any trouble spots - trust me, you'll notice them. It's almost like microphone feedback. Once you find one, turn the level back to zero and then start turning it down a bit at a time (preferably flipping the EQ on and off to hear the difference) until you're happy.


    In order to narrow the EQ band, I understand that will involve increasing the "Q" parameter. Is there a certain Q "sweet spot" level that you would recommend for this setting when using this frequency sweeping method. I assume it will be at a relatively high level, but I imagine if it is too high, it may make the window too narrow, and make it easier to miss the offensive frequency range when sweeping through the spectrum. The sensitivity and "taper" on the KPA's edit knobs may make this even more challenging. So, what Q level, on the KPA's Studio Equalizer, would you use when performing this technique?


    I apologize if this is a stupid question...but once I have zeroed in on a particularly nasty frequency band, and I dial back the Gain/Level to reduce or remove it...would I be correct in leaving the "Q" parameter exactly as it is? Or do I turn it back to the original value? I apologize if this is a stupid question. I am guessing that I leave the Q parameter at the new (high) value, because if I then lower it to the original position, I presume I would start massively widening the frequency band that I have just cut, removing more and more (good) frequencies. Do I have that right? In other words, once I have cut the offensive frequencies, and am happy with the results, I leave the new, high Q value as it is, and just SAVE/Store the new Studio EQ settings for my Rig.


    Thanks again for all you help, mate.


    Cheers,
    John

    Edited 5 times, last by Tritium ().

    Quote from Lokasenna

    Now, as for the buzzing on your note tails... may I ask what power amp and FR speaker you're using? I had a similar issue with my Crate Powerblock and Xitone wedge, and it turned out to be a combination of a damaged tweeter and the Powerblock starting to crap out. Anything that produced a big "oomph", like a palm mute on the low E, would have a bit of a crackling buzz on the tail.


    Hi Lokasenna,


    I almost forgot to answer your question at the end of your prior post.


    The quasi "FRFR" monitor that I am using is, funnily enough, also a Xitone passive 1x12 Wedge. It is interesting that you brought up the HF compression driver.


    The XiTone site provides detail on the main driver, which is an Eminence BETA-12CX. However, there was no published information on what the co-axially mounted HF compression driver. I did a bit of research on the BETA-12CX, and Eminence recommends their model ASD:1001 HF Driver. I sent Mick at XiTone an email asking him if this was the HF driver he installed on my Wedge. It isn't. For some reason, Mick is using an HF driver made by a Brazilian company called PRV Audio. Specifically, the driver is a PRV D230Ti-S.


    Here is a direct link to PRV Audio's site, and the D230Ti-S:


    http://prvaudio.com/products/d230ti-s/


    I suspect that this driver is a cheaper unit, versus the Eminence ASD. I am pretty sure that Mick used the Eminence ASD on earlier Wedges...but evidently made a switch to the 3rd-party PRV Audio driver. I now wonder if this PRV driver is low quality and/or defective, and may be the root cause to my harshness and buzzing problems...just like you mentioned!! The mother-fu**'ing plot thickens. X(

    Edited 2 times, last by Tritium ().

    A basic "demonstration" of how the Q factor ("quality factor") "works" is posted on the second page Paul linked.
    As for its definition, it's a bit non-intuitive actually. Q is defined as the ratio between the central frequency of the "bell" (expressed in herz) and the band width, defined as the range of frequencies where the filter can act with at least a 3 dB interview.
    Look at this image: https://upload.wikimedia.org/w…ommons/f/f6/Bandwidth.svg
    The Q factor is defined as fc/f2-f1.
    This means that, if the centre freq is say 500 Hz and you set Q=1, f2-f1 must equal 500 Hz. That is, the bell is "large" 500 Hz (from 250 to 750 Hz).
    If you set Q=10, the bell shall go from 475 to 525 Hz only (that is 50 Hz, or 1/10 of 500): the filter operates on a much narrower band of frequencies.


    Now, what if you keep Q=1 but move the bell centre from 500 to 5000? Since f2-f1 has always to equal 5000, its width will be between 2500<->7500 Hz.
    General rule of thumb (as per the above-shown examples): if you want to operate on a narrow range of frequencies, Q has to get bigger as much as you move the central frequency up.


    :)


    Excellent info. and explanation, Viabcroce.


    Much appreciated!

    Quote from Lokasenna

    The answer to your question about sweeping the frequencies to get rid of harshness is down at the ***s.


    :)


    Just wanted to thank you again, Lokesenna, as well as Paults and Viabcroce.


    I have already made fantastic improvements in mitigating the bothersome buzzing on the trailing decay of distorted note, by adding the Studio Equalizer to the "X" slot, and incorporating the information you provided. It turns out the Studio EQ is uber powerful, when used and tweaked appropriately. Not only have I been able to reduce the harshness caused by certain troublesome frequencies, I have actually improved the lead/solo tones I am getting. This has been a huge help.


    By the way, I just ordered an Eminence ASD:1001 HF compression driver, to replace the PRV Audio HF driver. I was a bit disappointed when I learned that my XiTone wedge was not supplied with the HF driver that Eminence recommends for their BETA-12CX. I expect that once I swap these, I will notice even more improvements.


    Cheers,
    John

    Quote from Lokasenna

    Oops, I actually meant to say woofer, not tweeter - Mick shipped me a new Beta 12CX, since the issue was there from day 1, and that mostly cleared it up.


    Well, I did perform the "frequency sweep" technique you described, using the Studio Equalizer, and there is some weird shit going on around 3000 kHz and 4800 kHz. So, that is why I was leaning towards the installed HF compression driver as potentially being the problem. No big deal. Even if the HF driver isn't the source of the problem, I expect the Eminence ASD:1001 will be a superior HF driver versus the PRV Audio. Has anyone heard of this company (PRV Audio), before? Has anyone any experience with their speakers?


    Another possibility could be faulty crossover circuit. When I install the ASD:1001, I will be checking the crossover board. I know what make/model crossover circuit board I would expect to find...so it will be interesting to see if this is the case. I certainly hope no corners were cut, here, on this critical component.

    Okay, this is interesting...


    I just swapped out the PRVaudio HF driver, that was installed in my XiTone 1x12 passive Wedge, with the Eminence ASD:1001. All the "noise" problems I had been experiencing have completely disappeared. In fact, the difference is so great, that I have been able to actually TURN OFF many of the stomp noise-gates I had installed on various favorite Rigs. I also was using the KPA Studio EQ effect as more of a band-aid, to compensate for the HF noise and harshness that I was experiencing when using my KPA with the XiTone.


    I did not expect such a dramatic change. I actually am a bit perplexed. It was definitely the HF driver. Nothing else has changed -- same guitar, same pickups, same cables, same power, etc.


    So, either the PRV Audio HF driver is a sub-standard design...or there is a manufacturer's defect in my particular driver (although nothing is apparent, from just a visual inspection). Has anyone had any experience with PRV Audio speakers? Has anyone even heard of this Company?


    In any event, all is well that ends well.

    Quote from Zapman

    Nope, Tritium, never really heard of them but I sure am glad for you that things have made you smile and you can now enjoy the KPA again!! :thumbup:


    Thanks, Zapman.


    Yes, all is well in KPA land. I was getting so frustrated with the XiTone's behavior with the KPA. It is weird, in that while I was aware of the strange HF distortion/noise when I first got the XiTone, it wasn't immediately disconcerting...as I chalked it up to having to learn how to dial in my KPA for the idiosyncrasies of a FRFR-type monitor. Before I got the XiTone, I was using my Tech21 Power Engine. However, as the weeks and months went by, the distortion/noise issue became much more annoying. I couldn't dial it out, and once my ear had become more sensitive to it...I started noticing it even on lower gain rigs/profiles that previously weren't troublesome.


    But now that the "questionable" HF driver has been replaced with the Eminence ASD:1001 (which should have been matched with the Eminence Beta-12CX in the first place), well, it is like night and day. And, for the record, it wasn't in my head. There is no question that noise/distortion was caused by that PRV Audio HF driver.


    If any fellow KPA owners happen to own a XiTone wedge, and read this thread/post...it would be interesting to hear your feedback as to whether your XiTone was supplied with the recommended Eminence ASD:1001 HF driver for the coaxial Eminence Beta-12CX, or with the "no-name" PRV Audio HF driver.


    Cheers all,
    John