1st Order Butterworth Filter / Guitar Tone Control

[State of Epicicity]

I've read that a guitar tone knob is a 1st Order Butterworth Filter, and I'm wondering if there's a good way to recreate this in the Axe. Thanks!

 

[Dave Merrill]

6db/octave lowpass in the filter block. Not at my Axe but I think we've got that.

 

[Honken]

I've read that a guitar tone knob is a 1st Order Butterworth Filter, and I'm wondering if there's a good way to recreate this in the Axe. Thanks!

Do you mean something like the sound radix surfer eq?

 

[Honken]

From the wiki:

An ideal electrical filter should not only completely reject the unwanted frequencies but should also have uniform sensitivity for the wanted frequencies".

 

[State of Epicicity]

Do you mean something like the sound radix surfer eq?

Oh no, I was just wondering what the actual slope of a guitar tone knob usually is! I'd like to see about using a Filter Block instead of my tone knob to have perfectly recallable tone knob settings, essentially.

 

[State of Epicicity]

6db/octave lowpass in the filter block. Not at my Axe but I think we've got that.

Awesome! Thanks so much for that. I am seeing in the Filter Block the LowPass with 2nd or 4th order available. But I think maybe the way to do this is in the PEQ Block, where you can choose, for Band 5, a Blocking Band type, then you can choose 6 db/Oct! Very much appreciated.

 

[State of Epicicity]

6db/octave lowpass in the filter block. Not at my Axe but I think we've got that.

Okay, and looking further, maybe there is a way in the Filter Block, but choosing the Allpass type. There it allows for a 1st order selection.

 

[guitarnerdswe]

If you're going to simulate low resistance values (like the tone off or close to it), you're going to need to add a bump at the cut off point. Where this bump is frequency wise, depends on the capacitor value you're going for.

 

[State of Epicicity]

I'd you're going to simulate low resistance values (like the tone off or close to it), you're going to need to add a bump at the cut off point. Where this bump is frequency wise, depends on the capacitor value you're going for.

Oh cool, do you know how I calculate that? I do use really low cap values.

 

[Honken]

Oh no, I was just wondering what the actual slope of a guitar tone knob usually is! I'd like to see about using a Filter Block instead of my tone knob to have perfectly recallable tone knob settings, essentially.

Aha! I've done this with the filter block. But that was for getting an instant jazz tone coming from very brutal metal. Kind of works but it's not quite the same, in my case. Maybe i need to revisit the patch i made.

 

[guitarnerdswe]

Oh cool, do you know how I calculate that? I do use really low cap values.

Well, you can't. It depends on the cables, pickups, wiring etc, and will vary greatly even with the same cap value. Even if you get a good approximation for one guitar, one pickup (or switch position), one tone knob setting and cap value, changing anything will throw all that out the window. Passive EQ is highly interactive. Just the nature of the best.

With that said, the closest thing to calculating it fairly correctly for any given setup is the GuitarFreak excel sheet.

https://guitarnuts2.proboards.com/thread/3627/guitarfreak-guitar-frequency-response-calculator

1. Go to the main tab.
2. Pick the closest pickup to yours on the left.
3. Set the frequency graph to "electrical only" (this will make the red line only show the electrical portion of the signal, sans strings, pickup position etc that don't matter for this experiment).
4. Click the "volume match" box above the GuitarFreak logo (makes the graph a bit easier to read when switching settings, pickups etc).
5. Turn the tone slider to preferred position.
6. Select the preferred cap value.

There are other things you can play around with, but this will get you into comparing caps the fastest (and also switch pickups etc). Important to note that the cap value has basically no affect above 5 on the tone knob. As you get closer to 0, the caps own cut off slope takes over, and 12 dB/oct (second order fitler) is much closer to what's going own. I would suggest as @Brucegregori did, and use a filter block. Set it to low pass, and bump up the Q to get that bump right at the cut off. I managed to get passable results in a couple of minutes. Of course, I needed different values for freq and Q depending on the pickup selected (and when using series vs parallel for a humbucker).

 

[Brucegregori]

I actually use a filter block connected to my expression 1 sometimes. I set it depending on what I need it for - lots of times it is great for slide playing. It actually can sound "wah" like but not as aggressive. I found this works better than using the wah which can get to honky. One setting is to kind of roll the the tone down. Experiment with it as it is a good under used feature. I also like it for just a subtle mid boost - great for cutting through a solo a bit....

 

[State of Epicicity]

Thanks so much to everyone offering suggestions here!

@Honken Awesome. I ended up experimenting a bunch last night and, finding the right slope, I totally felt like I was messing with my volume and tone knobs, but on the unit instead of my guitar! Now I can save “volume and tone knob” settings easily and recall them exactly.

@guitarnerdswe Thanks so much for that. I’m a lurker on the Guitar Nuts 2 forum, trying to glean what I can from there, and I have used Guitar Freak for other purposes before; it is a wonderful resource, and something I could totally use here.

@Brucegregori That is a cool idea; you’re right, like a very specifically configurable wah. I am considering incorporating an expression pedal to go between different sets of frequencies in a PEQ block right after the input to get different pickup characteristics being the regular tone control.

 

[Handyman]

A guitar with passive electronics and a tone control isn't just a 1st order filter - its quite a bit more complex than that as it interacts with the inductance of the pickups.

A 1st order low pass filter would just roll off high frequencies. But as the pickup is attached to the whole thing, turning the tone knob also decreases the resonant peak caused by the combination of the pickup inductance and various capacitance sources.

You can of course build really complex filters with the PEQ block, but but its not going to feel quite like turning the tone knob on your guitar unless you put some work into it.

 

[Brucegregori]

A guitar with passive electronics and a tone control isn't just a 1st order filter - its quite a bit more complex than that as it interacts with the inductance of the pickups.

A 1st order low pass filter would just roll off high frequencies. But as the pickup is attached to the whole thing, turning the tone knob also decreases the resonant peak caused by the combination of the pickup inductance and various capacitance sources.

You can of course build really complex filters with the PEQ block, but but its not going to feel quite like turning the tone knob on your guitar unless you put some work into it.

You can get pretty close using multiple filter blocks...and depending how your tone is wired. It is work - yup but really handy in dark places lol.

 

[Maddface]

Bring up the RTA block in the axe fx. Turn your tone control knob and see what the block reads. Copy that.

 

[FractalAudio]

A guitar tone control, by itself, is typically a first-order filter. However the source impedance of a pickup is complex so you can't replicate it with just a simple filter.

 

[tealtonerick]

A guitar tone control, by itself, is typically a first-order filter. However the source impedance of a pickup is complex so you can't replicate it with just a simple filter.

Yes, quite.

State Of Epicicity, if you would like to dig in to how to calculate these things a little more closely, please take a look at the attached docs...

 

[State of Epicicity]

Thanks so much for all these replies; I really thought no one at all might care a whiff about this!

@tealtonerick Much appreciated. I will absolutely read these to gain a better understanding. At first blush, they look like a perfect resource.

 

[FractalAudio]

This is not to say that a simple lowpass filter can't be used to great effectiveness. In the Filter block the High Cut parameter controls a first-order lowpass filter. It won't behave exactly like a guitar's tone control but it might be just what you need.