General Distortion/Overdrive tone shaping discussion

[Fancy Lime]

Hi everyone,

I played around with guitar distortion and overdrive recently and thought I'd share some of my experiences with tone shaping in the hope that others contribute theirs so that this thread can be a quick primer for those starting to develop their own dist or od pedals.

Light guitar dist/od:
Here I like to boost treble with a corner frequency of about 800Hz (6db/oct) before or in the clipping stage and do only mild tone shaping after the clipping, other than rolling off treble with 12db/oct at around 4 - 6kHz. A Rat-style treble control works best for these things IMHO.

Heavy guitar dist:
Again, the same treble boost as above before the clipping stage(s). Allowing more bass in makes it fuzzier, which can also be a nice. After clipping, a low mid cut of about 15-20db at 200-300Hz helps removing muddiness and helps separate guitar and bass in the final mix (if the bass is appropriately eq'd as well, see below). The mid cut can be implemented quite easily with a bridged-T filter. 10-20db bass boost post clipping with a corner frequency of 100Hz gives the sound a lot of punch for down-tuned Metal. A boost at 800-2000Hz gives definition and bite. Over 3kHz things get screechy. I recommend cutting highs with 12db/oct above 3-5kHz, depending on how much device the thing has (more gain = lower cutoff). For tone controls, I like me a baxandall or james tone stack after clipping for this kind of device.

Light bass dist/od:
For low gain, I like to go into clipping with a full-range signal or with only a mid-cut centered at 800Hz. The mid cut gives the guitar more space and also makes the bass sound fatter. Having the mid cut before clipping means that the mids at 800Hz are more dynamic than lows and highs and not quite as strongly cut as when you put it after the clipping. If I want a variable bass control, I like to have it before the clipping as well, so I can use it for tone shaping. The clipping itself can be made asymmetrical in order to retain more fundamentals and dynamics. Rat-style high cut after clipping is again my first choice for raining in the treble on this kind of pedal.

Heavy bass distortion:
Before the clipping stage, I like to boost treble with a corner frequency of ca. 1500Hz, else it becomes a fuzz. Making the treble boost / bass cut variable is great for versatility but full bass into a high gain clipper quickly becomes more of a special effect (for intros or other "bass only" parts) than a bass sound that is useful in the band context. Strongly asymmetric clipping is even more useful here than with the lighter bass drive. I like to just put one diode to ground instead of an anti-parallel pair. Post clipping, I cut the mids again with a bridged-T filter at 800Hz. Over 3kHz things get screechy. I recommend cutting highs with 12db/oct above 3-5kHz, depending on how much device the thing has (more gain = lower cutoff). For tone controls, I like me a baxandall or james tone stack after clipping for this kind of device.

What are your experiences and opinions on frequency shaping in distortion or overdrive pedals?

Cheers,
Andy

[dschwartz]

That's great info!
For my designs, on high gain i also add a lpf pre- distortion, the higher the gain, the lower the cutoff freq, reaching almost 2khz at full gain. It is great to get a cleaner, les hissy and more stable tone.

[Rob Strand]

Good recipes.

corner frequency of about 800Hz (6db/oct)

That's always good starting point (IIRC TS-9 and many others works out at 720Hz).  Going lower is OK for light drive but in the long run the 720Hz figure just seems to work.

What I've found about 12dB/oct filters is it takes all the junk away and makes the sound less dependent on the speaker and amp settings.   It's also more likely to sound less objectionable - something I've noticed in amp shoot-outs.   When you go for an ultra-transparent sound it's a very delicate balance of filtering to get the highs right.  I often take that sound then compare it against something with heavier filtering or a TS-9 and you always find there's something good and something bad about keeping the highs.

This type of blues sound, loses something when you take off too much off the highs,
https://www.youtube.com/watch?v=6P8N5HiF5-8

On the other side of the scale Frank Gambale's heavier distorted tone pretty much strips off the upper highs.
https://www.youtube.com/watch?v=R-9EQV9B0FQ
https://www.youtube.com/watch?v=o6pSaHQcIJs

[iainpunk]

here are my personal favorites

light od/ds:
my favourite DIY overdrive/distortion uses a first order highpass around 250-300Hz, folowed by jfet clipping, no further treble cut because jfets sound quite warm to begin with. works great for guitar, terrible for bass.

extreme guitar distortion:
i find for this purpose, a dirty (read: super filthy and rancid) boost is more usefull.
low gain hard clipping at full range, (which is a bit fuzzy, but creates a bunch of overtones to be boosted later on) followed by a 1kHz boost of up to 30dB which really makes the sound grind, especially when the midboost is at max. send that into a lightly overdriven amp to get to grindcore/deathmetal/crustpunk/D-beat Valhalla!!!

heavy guitar distortion:
two paths
A) second order filter @750Hz into variable gain 1kHz boost into soft clipping gain stage with high threshold into hard clipping at a lower threshold so you get the hard clipping sound without making the opamp clip, sounds cleaner. followed by a resonant low pass filter with a cutoff at 3kHz and a boost of 3 to 6 db just to add a bit of chime and take away the noise above 3.5kHz.
B) run a parallel bass path putting the clean signal into a first order a bandpass around 80Hz.
add the two paths together wit a set amount of distorted path but a variable amount of bass path.

bass distortion:
clean boost into big muff tone stack followed by half wave precision rectifier. followed by a rat style filter.

pure noise pedal:
full range into a wave folder with clipping diodes in the feedback loop to cancel out all fundamental frequencies, leaving only the sweet sweet sound of non-harmonic distortion.


(UK style) punk rock distortion:
two paths,
a) 2nd order high pass with cutoff at 1kHz band boost of 6db at 3kHz to get a lot of natural guitar higher harmonics
b) low gain full range boost into hard clipping to get a bit of a fuzzy lofi tone, lowpass filter at 800Hz
mix those to get a warm low end and a clean treble spectrum to really bite and jump. the treble is very dynamic while the low end is also dynamic but less so.
best to be played with parallel bar chords. also great for ska/reggae music

good luck and stay hydrated
- iain

[patrick398]

Also known as the Batman distortion

I'm not savvy enough to tell you specifics of corner frequencies etc but I have a circuit on the breadboard at the moment which i'm really enjoying. The first section is a fixed gain RC4580 stage with this kind of tone shaping arrangement:

I'm not sure if it has a name...

The 4580 is feeding a silicon/germanium hybrid class A preamp kind of thing which has it's own gain control but the output volume from the 4580 acts as a kind of 'pre-gain' and it can go from sparkly clean boost to full on slammed fuzz. I've been experimenting with different filters and tone stacks after the final gain stage and haven't decided on one yet but find that pre and post gain filtering provides a great deal of versatility.

[PRR]

> I'm not sure if it has a name...

Baxandall.

[patrick398]

That's funny, all these years i thought the baxandal was something totally different 

[Fancy Lime]

That's funny, all these years i thought the baxandal was something totally different 

Did you think of the "James Tone Stack", which is sometimes (and not entirely accurately) known as the "passive Baxandall"?

Andy

[iainpunk]

Also known as the Batman distortion

badman distortion, that is genius rofl

[PRR]

...i thought the baxandal was something totally different ...

An art historian?

Peter Baxandall is one of the giants we stand on the shoulders of.

[patrick398]

...i thought the baxandal was something totally different ...

An art historian?

Peter Baxandall is one of the giants we stand on the shoulders of.

Here in London it's a way of carrying your Bax. A bax 'andle 
Or a large flip flop style thing for a persons spine. A back sandal.

[antonis]

That's funny, all these years i thought the baxandal was something totally different 

Not "totally" but a "bit" different, for sure.. 

Original Baxandall was a bit more complicated (mainly on its calculations) with more caps & resistors with 10/1 scaled values..


Your Bax is what so called "Americanized Baxandall"..

[PRR]

> Original Baxandall was a bit more complicated (mainly on its calculations) with more caps & resistors with 10/1 scaled values..

No.

The 10:1 ratios, and no amplifier inside, make what we usually call a JAMES, after the man who wrote-up several ideas in one article.

Bax: http://www.learnabout-electronics.org/Downloads/NegativeFeedbackTone.pdf
James: http://www.thermionic.info/james/James_SimpleToneControl.pdf

[Rob Strand]

I wonder who invented the "single cap" variants of the Baxandall?
ie one cap on Bass side and one cap on the Treble.
Then there's all the combinations of Treble and Bass.
There's the Treble variation with a resistor on the Treble pot wiper instead of the pot cw and ccw terminals.