Does a basic guitar tone knob work like a low pass filter?

  • Does a basic guitar tone knob work like a low pass filter you would use on a EQ plugin? And is that the same as using the High Cut parameter in Kemper?


    What about when you use a treble bleed circuit? How would one mimic that on an EQ?

    The more you find what Kemper can do then the harder you try to find what it cannot do -- like make a good cup of Frappuccino.

  • My guess is the tone knob and the DAW EQ will have slightly different effects due to the tone knobs loading effects on the pickup. But it may be a very small change???


    The DAW EQ will simply roll of the high frequencies.


    The tone knob will change the impedance the pickup is driving.


    Lets say you have 250k pots and are driving a 1000k amplifier. Your pickup is trying to push voltage into two parallel 250k's that are in parallel with the 1000k load. That is 111k load.


    Now you turn the tone knob 50% off. So you have a 250k in parallel with 125k in parallel with 1000k. That is a 76k load.


    Since the tone knob is driving a capacitor normally, these values are not valid. The load will change with frequency. Just wanted to do the math in my head to see if I was completely nuts.


    My complete noob guess is the resonant frequency (the WAH part or voice) of the pickup will change. I think a similar thing happens when adjusting the volume knob.


    Someone smart can come and clear this up for us :wacko:

  • I don't know about smart, but an electrical engineer at least :).


    From here: https://miro.medium.com/max/14…LzFj-r0rv_JmGntXulf1g.png


    Imagine your pickup is basically a sine wave generator (it isn't of course), and some resistance. Your tone pot has a resistor and a capacitor. The capacitor can't change (without you getting a soldering iron out), and the tone pot is a variable resistor that can go from nothing (a hard piece of wire like it isn't there at all) to either 250K Ohms or 500K Ohms (these are the most common).


    Capacitors present a dead short at very high frequencies and present a complete open circuit for DC signals (ones that don't move up and down at all). This is important you can see as the more of the signal you allow to go through the cap (ie, you lower the resistance on the tone pot toward zero), the less high frequencies will make it through and onto the volume pot.


    Note, that even when you have your pot turned all the way up, there is still SOME high frequencies going through the capacitor. The higher the resistor value, the less this is true.


    Also, just a note, there are several different ways to wire up your tone knob and volume control to your pickups. I have shown only the most simple one for the purpose of explanation.


    This guy goes through this simple setup in a video here:


    Note: In this video the internal resistance of the pickup is ignored.

  • Oh, BTW, your thought on how the pot works is ACTUALLY how a WAH pedal works (or at least a simple one) The actual circuit used in a WAH pedal is called a band pass circuit. The variable resistor in a WHA is used to change the center frequency of the bandpass.


    A bandpass filter squelches the HF beyond a point AND the LF beyond a point allowing only a band (Q width) of frequency through.


    The biggest failure mode with the WHA pedal is the resistor wears out from the repeated sweeping contact over the resistor coil.


    If you are interested in the brain crushing details of an active band pass circuit, you can see it here: http://www.geofex.com/article_folders/wahpedl/wahped.htm


    This is more complex since, unlike your guitar tone knob, there are powered circuit elements that have behaviors that are much more difficult to describe. Analog amplification circuits were long ago replaced with operational amplifiers that keep a host of analog circuitry goodness concealed from we engineers so we can simply rely on the Op Amp to just amplify the signal like we want it to without having to do a metric ton of math to figure it out (engineers are lazy) :).

  • I don't know about smart, but an electrical engineer at least :).

    Thanks for chiming in! I was hoping you would. I was even going to drop your name in my first post.


    Engineer here also. But I spent my whole career doing programming and system integration. So I do not have a ton of day to day use of my degree. Just enough to be dangerous and sometimes lead people astray 8o


    When I first started going to school I had dreams of making a pedal switcher and modding some amps etc. Once I bought a computer, I started programming and never looked back. Now I am not good at either engineering or programming. Trained in the one I dont use, self taught in the other.

  • Thanks for chiming in! I was hoping you would. I was even going to drop your name in my first post.


    Engineer here also. But I spent my whole career doing programming and system integration. So I do not have a ton of day to day use of my degree. Just enough to be dangerous and sometimes lead people astray 8o


    When I first started going to school I had dreams of making a pedal switcher and modding some amps etc. Once I bought a computer, I started programming and never looked back. Now I am not good at either engineering or programming. Trained in the one I dont use, self taught in the other.

    I Have done a good amount of both hardware and code, but I too am self taught in code. I have been in management for over 15 years, but still sneak off and write code or do some hardware design once in a while when no one is looking 😀. Now days I pretty much make presentations and go to conferences.


    I did make a custom back panel for my Kemper rack and replaced the RJ45 with an Ethercon ony Kemper remote cable.


    When my daughter asked what I do as an engineer, I told her I mange people who manage engineers 😁.


    It's great when I get to brush off my old skills though. I was once a damned fine engineer!


    Maybe when I retire I will do a board or so now and then for travel money in retirement

  • All I want to know is if the graph looks like this? ^^^^^^


    Looks like a low pass filter EQ to me that I could match with a DAW EQ...


    In Passive Mode:

    The typical Tone Control response is shown below in the passive mode.

    HIGH FREQUENCY RESPONSE - TONE IN PASSIVE MODE


    Treble roll off position: Black - 100%, Red 66%, Green 33%, Blue 0%

    These curves were acquired using a Nordstrand NJ5 pickup connected with a 10' cable into an Avalon U5 preamp.

    The frequency response at the top end changes depends on the pickup, cable, and loading amplifier (Since the preamp is bypassed and can not buffer the pickup signals, the frequency change is directly dependent on the pickup, cable, and loading amplifier).


    Source: http://www.audereengineering.com/3ZB_Tone.htm

    The more you find what Kemper can do then the harder you try to find what it cannot do -- like make a good cup of Frappuccino.

  • Looks like a low pass filter EQ to me that I could match with a DAW EQ...

    good luck, it is actually much harder than it looks.
    the cutoff frequency doesn't seem change that much, but the roll of (dB per octave) does.
    turned all the way down, you even get a resonance.

    so far, I never heard a convincing tone knob simulation from an EQ.
    this would also only work in a reamping scenario, since the tonal change is of course pre gain

  • good luck, it is actually much harder than it looks.
    the cutoff frequency doesn't seem change that much, but the roll of (dB per octave) does.
    turned all the way down, you even get a resonance.

    so far, I never heard a convincing tone knob simulation from an EQ.
    this would also only work in a reamping scenario, since the tonal change is of course pre gain

    I recorded a nice tone previously and wanted to duplicate it again but I could not. Then I remembered I rolled the tone knob down but can't remember how much. (I should have noted it somewhere). So, I was hoping to create 3 or 4 low pass filter presets to represent a percentage tone roll off to apply on the DI reamped track, and then I can add those for my toolbox later on.


    I know I am guilty of thinking way too far ahead of my current musical skills but I like difficult tasks. ;)

    The more you find what Kemper can do then the harder you try to find what it cannot do -- like make a good cup of Frappuccino.

  • I would be VERY surprised if you could duplicate it in the DAW EQ. The reason being that the guitar tone knobe is changing the sound before the Amp but DAW is after. The guitar EQ changes the distortion characteristics as well as general tone. Test this by using a Studio EQ with your example settings and listen to the difference with is in Stomps Vs Effects.

  • I would be VERY surprised if you could duplicate it in the DAW EQ. The reason being that the guitar tone knobe is changing the sound before the Amp but DAW is after. The guitar EQ changes the distortion characteristics as well as general tone. Test this by using a Studio EQ with your example settings and listen to the difference with is in Stomps Vs Effects.

    I would apply it to the DI when I reamped.

    The more you find what Kemper can do then the harder you try to find what it cannot do -- like make a good cup of Frappuccino.

  • As mentioned, this is an oversimplification. All of the above is relatively incorrrect depending on how accurately you want to understand how the pickups, control, cables, etc.. work as a system.


    I attached a file that I found on the web several years ago. It will either help you understand fully, confuse you, or make you decide that you would rather not know. GuitarFreak_6_60_051219_xlsm.pdf Due to allowed extensions I had to rename it as .pdf. Download it and rename to GuitarFreak_6_60_051219.xlsm.


    Have fun


    BTW, the answer to your original question is that it kinda acts like a low pass filter in a first approximation. The devil is in the details and in the end there are quite a few factors that can contribute to errors of that approximation.

  • Yes. It was an oversimplification. In my first response I wasn't sure of the OP's background so I kept things as simple as possible.


    The actual circuit is more complex because the pickups are big inductors that are being driven by metal strings that interact with those inductors making the entire circuit a serious PITA to analyze as it is seriously more complex than just an simple LRC circuit.


    I felt my explanation was enough to understand basically what is going on with the tone knob without attempting to teach the entire board how to setup a pSPICE simulation that accurately models all the things going on with an electric guitar ;).


    .... and I agree. It is "kinda like" a low pass filter.

  • good luck, it is actually much harder than it looks.
    the cutoff frequency doesn't seem change that much, but the roll of (dB per octave) does.
    turned all the way down, you even get a resonance.

    so far, I never heard a convincing tone knob simulation from an EQ.
    this would also only work in a reamping scenario, since the tonal change is of course pre gain

    I agree. For all the reasons I mentioned above (and likely a few more that I missed), it isn't just a simple LPF.

  • So it's kind of like a LPF just not a simple LPF. Okay. Got it! I'll just make my EQ preset more advanced. ;) ^^

    The more you find what Kemper can do then the harder you try to find what it cannot do -- like make a good cup of Frappuccino.