Anyone know of existing pedals that do something like this? I'm starting to think up something using pass filters to split the signal and send it to separate processing sections then combine them at the output. What got me onto the idea was a live Govt Mule song I heard recently where Warren's guitar sounded "moderately" clean on the lower notes but as he went up the neck the notes got a great OD tone. It caught my ear right away as it really stood out. One thing I noticed was that low volume difference between the more overdriven notes was not really any louder than the lower notes. Not what I have experienced with common treble boosters.
The trick will be figuring out the filters. The OD sections can be any of the generic designs just tweaked to the range of frequencies being handled. Then maybe a blend pot at the end or just voltage dividers to set a balance. Breadboard here I come.
I'm sure I read about a Craig Anderton design that did something like that - split the signal into low and high, distort each separately, add them back together. I'll post something if I can find it.
It's this:
(https://i.postimg.cc/F1Fyg4Nr/QUADRAFUZZSCH.gif) (https://postimg.cc/F1Fyg4Nr)
It's okay. Not fabulous. My gripe is that the gain needs to be adjusted for the different bands, given their respective acoustic energy. Craig set the gain identically for each. But if the goal is strong control of the tone, it holds up.
The Yamaha MDB-100 also tinkers with the idea, but doesn't provide enough control:
(https://i.postimg.cc/7JCbsXKV/YAMAHA-MBD-100.png) (https://postimg.cc/7JCbsXKV)
I tinkered with a 2-band approach, that was okay, and certainly easier to make, but not inspiring:
(https://i.postimg.cc/SJFybyRq/Flexidrive-schem-v3.png) (https://postimg.cc/SJFybyRq)
there's also this dual band FET overdrive from almost 10 years ago, Blüe Monster, from forumite Bengt:
https://www.diystompboxes.com/smfforum/index.php?topic=99142.msg877443#msg877443 (https://www.diystompboxes.com/smfforum/index.php?topic=99142.msg877443#msg877443)
it can be fun to play with gyrators (simulated inductor filters), or full on VCF stuff, although it gets a little more into psychedelic territory
+1 on needing to adjust gain for each band. Deafbutpicky's Thrice used three bands of CMOS and is nice. Link to other forum where missing Schematic was reposted:
https://www.freestompboxes.org/viewtopic.php?f=10&t=25632&p=246874&hilit=deafbutpicky&sid=9457146260f1ff0f4053690cefb81345#p246874 (https://www.freestompboxes.org/viewtopic.php?f=10&t=25632&p=246874&hilit=deafbutpicky&sid=9457146260f1ff0f4053690cefb81345#p246874)
I think when I tried this I also added separate volume for each band. If your'e going to adjust gain, better do volume too.
Easy enough experiment for two bands to use a splitter mixer and "any" two distortion boxes with "any" tone controls.
Another pedal, dealing with 2 band distortion, though not "crossovered" like the examples above, is old MXR Distortion II
There are different goals of using multi-band clipping.
One, which Anderton/PAiA explored is to reduce intermodulation distortion, such that the focus is squarely on harmonic distortion. Applying gain to narrow individual-band clipping circuits reduces intermodulation.
Another goal is to be able to apply clipping more evenly across the fretboard. Or, its complement, applying it differentially.
A third goal is to be able to extract very different sounding tones by control of individual bands.
Quote from: Mark Hammer on July 31, 2021, 11:35:44 AM
It's this:
(https://i.postimg.cc/F1Fyg4Nr/QUADRAFUZZSCH.gif) (https://postimg.cc/F1Fyg4Nr)
It's okay. Not fabulous. My gripe is that the gain needs to be adjusted for the different bands, given their respective acoustic energy. Craig set the gain identically for each. But if the goal is strong control of the tone, it holds up.
The Yamaha MDB-100 also tinkers with the idea, but doesn't provide enough control:
(https://i.postimg.cc/7JCbsXKV/YAMAHA-MBD-100.png) (https://postimg.cc/7JCbsXKV)
I tinkered with a 2-band approach, that was okay, and certainly easier to make, but not inspiring:
(https://i.postimg.cc/SJFybyRq/Flexidrive-schem-v3.png) (https://postimg.cc/SJFybyRq)
Aha! Thanks Mark! That saves me racking my brains trying to remember it! It
was that!
That Flexidrive design looks like a lot of time was spent on tone control values *all over* the circuit! Looks like evidence of a lot of tweaking to me. ;)
In a similar vein, but with a hefty dose of "too much is not enough" :) I'm working with a friend on an adjunct to his son's mic'd flute. For background, in the 1970s I did a lot of thought about extracting frequencies in bands from a guitar signal and processing them similarly or differently. Built a few of the filter bands, and largely abandoned it for a few decades.
Along comes Friend A, who wants to extract the fundamental of a flute and synthesize accompaniment for it. I pointed him to the Harmony Generator from E&MM, but that wasn't quite enough for him. We talked and over time he talked me into ressurecting some of the ideas.
The final implementation owes a lot to Rod Elliot's Real Time Audio analyzer design. I ... um, adapted... :) the filter circuits, as it was simply too easy not to. I put an SSM2166 compressor, five 1/3-octave filters, five envelope extractors, and five "I got signal!!" detectors along with an FPGA implementation of the MK50240 top octave generator and a PLL to lock the TOG to a fundamental in an equally tempered notes way onto one PCB. The board is 3.9" square. The full implementation uses two boards stacked to get ten 1/3-octave bands to cover the flute fundamental range. Board also contains a priority encoder/selector to pick the lowest-frequency filter output, which is, presumably the fundamental, at least for flute.
It's a busy design. It's all SMD, with TSSOP ICs and 0603 Rs and Cs. More about it if you're interested. As an offshoot, I got the TOG circuit on a two layer board that plugs into the footprint of the actual MK50240. It's not a drop in, as it has to run from 3.3V, not 10 or 12.
Thanks, Tom. Yeah, I took advantage of every possible locus in the circuit to keep the top and bottom separate; not just prior to clipping, but after as well. I was aiming for simplicity by making the gain control reciprocal (i.e., more gain for the one side = less gain for the other). But in retrospect, separate Gain controls for each channel would have been smarter. Less elegant, but better control. Alternatively, perhaps a parallel resistor or two on one or even both legs of the drive/gain pot might yield a smoother transition in the individual gains. I just used a linear pot, crossed my fingers and hoped it would work out. There's more gain on tap for the mids+highs section, courtesy of R16 vs R8, but that really only enters into the equation as one approaches the treble end of the drive-balance pot. As can be the case with many things, pot taper can be critical.
Wow! Thanks for all the input guys. Keep it coming. Mark, I now recall see the Flexidrive previously. I may start there as it's certainly a simpler design than the Anderton. Sadly all the other links folks posted come back as dead as far as schematics and soundclips go.
Idy, I had though of your idea of a splitter mixer with two pedals as a basic start to see what gives. As others have pointed out there might be phase and IM issues but it's an easy "toe in the water" so to speak.
Researching W. Haynes rig after my initial post shoes a handful of known pedals. Klon and a Diaz Texas Ranger are the two that I think might be the source of the tone, but I have not played either so I have no idea. He also runs multiple amps simultaneously through a Bradshaw rig... so who knows. Still a worthwhile project I think. Might not payoff but I'll never know unless I try.
I've had the idea of doing this as a way of useing up all all 6 inverters in a cd4069, LP would go through a soft clip, and HP through a hard clip, then the two would mix via a "tone knob".
How about the Malekko Wolftone Sloika pedal
(https://i.postimg.cc/V0mJhwL0/C3345-DDD-A979-49-CD-8-A84-28027-AEA0977.png) (https://postimg.cc/V0mJhwL0)
I think there was something with a stereo pedal, that sent the lows to 1 amp and mids/highs to another. So as you played up the fretboard, the sound would appear to move to the second amp. Maybe it was in a dream, not sure ...lol. Maybe make it so rhythms and chords came out of both and as you dug in or turned up the gain the separation would increase.
(https://i.imgur.com/kAsb0Lu.jpg)
A couple other examples of the idea from INFANEM.
This may be a little more complicated than it needs to be. The Big Muff overdrives use capacitive coupling through antiparallel diodes in a transistor feedback stage to get isolation of low-frequency signals from the diodes to a greater extent than high-frequency signals.
For another approach, you could use a state variable filter with high, low and midrange frequency outputs and only apply distortion to the midrange. The lows would get too muddy if they were clipped and the highs would get additional unnecessary harmonic content, so if you just apply distortion to the mids, the world becomes a better place.
VFE Makes a pedal called Triumverate. This splits the signal into three bands and let's you set the drive and mix of each band. It's a lot like the the Quadra Fuzz but three instead of four bands. You can get this as a DIY project.
Darkglass X splits the signal in two, with separate Hof and left. There's a compressor on the low side and a drive on the high side.
Nothing much to add, just a "+1" from me for Bengt's Blüe Mönstër. Thanks Gary for posting the link - saves me searching for it! :)
Quote from: caspercody on July 31, 2021, 07:47:09 PM
How about the Malekko Wolftone Sloika pedal
Thanks Rob, this is new to me
https://www.youtube.com/watch?v=ov3xz20inlM
Sounds interesting.
I will study it deeper
Quote from: Mark Hammer on May 09, 2014, 10:28:56 AM
One of the things to keep in mind is that the different bands that one might split the signal into will likely have different average amplitudes. That, in turn, means that one either has to:
- pick your bands and bandwidths such that the output levels are approximately equal
- pick your split-points arbitrarily, and apply different amounts of post-split gain to each band in order to bring it up to similar clipping thresholds
- alter the clipping thresholds for each band to compensate for differential amplitude, or
- treat the differential clipping of bands having the same gain applied and clipping threshold as simply "the way the thing sounds"
My own tendency would be to work out whatever I could ahead of time to sidestep endless tweaking from the control panel. So, nothing adjustable about the split bands themselves, apart from their post-clip output level.
A half-dozen years back, I whipped up something for myself I called the Flexidrive, that simply used a 2-way split: middy-mids and highs, and lower-mids and lows. The split point was fixed, and I used one pot to adjust the gain of each side in reciprocal fashion, and another pot to adjust the relative balance between channels. That, and a master output control were all the knobs it had. Eventually I figured a toggle to set different levels of drive on the input stage would be a good idea. It had a lotta different sounds available. Can't speak to the intermodulation distortion, though.
I made some changes to what you see below, but this was the only drawing I could find and post at the moment.
(http://img.photobucket.com/albums/v474/mhammer/Flexidrive.png)
I think there might be some value in applying a similar strategy to a dual-band circuit, but use crossover distortion for the upper band. That is, place a back to back diode pair in series with the output of the gain stage. Personally, I find that x-over distortion likes bridge pickups, so feeding a series diode pair only mids and highs, combined with a clipped-and-filtered low end, might sound decent.
In retrospect, rather than a master drive control and a single pot producing reciprocal gain adjustment of the two clipping stages (i.e., more gain for one means less for the other), it's just smarter to have a drive control for each section, and be done with it. The nice thing about using those individual pots and a balance/mix control is that you can dial in relatively clean bottom OR top, and blend it with however dirty, or however much, you want of the other band.
Obviously doing that with more than two bands starts to get rather complicated, not least because you'd need two pots (drive and level) for each band, whereas a two-way split permits use of a single blend control: one less knob to find space for.
AHA!! Thanks for hunting that down Vivek.
Quote from: caspercody on July 31, 2021, 07:47:09 PM
How about the Malekko Wolftone Sloika pedal
(https://i.postimg.cc/V0mJhwL0/C3345-DDD-A979-49-CD-8-A84-28027-AEA0977.png) (https://postimg.cc/V0mJhwL0)
Not uninteresting, but I don't see much "band-splitting", just differential lowpass filtering of the resulting distortion.
Quote from: Mark Hammer on August 01, 2021, 07:59:14 AM
Quote from: caspercody on July 31, 2021, 07:47:09 PM
How about the Malekko Wolftone Sloika pedal
(https://i.postimg.cc/V0mJhwL0/C3345-DDD-A979-49-CD-8-A84-28027-AEA0977.png) (https://postimg.cc/V0mJhwL0)
Not uninteresting, but I don't see much "band-splitting", just differential lowpass filtering of the resulting distortion.
and some diode ladder stuff where piecemeal transfer function is also linked to frequency response ?
DeadEnd FX has a Infanem Driving Notion clone board called the DILLIGAF. Here is the build doc with a schematic (https://drive.google.com/file/d/156JFXVwj6Jt65MFF6aLoMADtHWMzEhl-/view). I seem to remember seeing forum posts saying it was particularly sensitive to biasing & transistor choice, but the build doc is recently updated with info on biasing, so maybe they've figured it out.
Question for ya. When R-C filters is there a best practice for any of the values? Playing around with the AMZ calc I see that you can make a filter for any typical guitar freq with a wide combination of values. .1 and a 4k vs .022 and an 18k for a 400hz low pass for example. I'd guess this was probably covered in basic audio circuit design 101 but I was absent that day. ;D
Thats a great question !!
Two filters where R1 x C1 = R2 x C2 will show the same frequency response curves
But their impedance will differ.
Normally there is a "Rule of tenth" or "Rule of tens" (It is just a good design guideline, not a legal requirement. Corners can be cut slightly)
It means: If there are stages that are connected to each other
The input impedance of a stage should be 10 times more than the output impedance of the previous stage
In your example, suppose the low pass filter fed a pot as a volume control
If you use 0.1uf and 4K, the pot could be more than 40K (And whatever is connected to the pot's wiper should have impedance more than 400K)
If you use 0.022 and 18k, the pot could be more than 180K (And whatever is connected to the pot's wiper should have impedance more than 1800K)
Hence, The Product of R and C is decided by the frequency response we need, but the exact value of R and C is decided by the impedance we want.
I played around with various clipping ideas a few years ago:
http://www.muzique.com/lab/tclip.htm
Best regards, Jack
Dear Jack
Thank you for your pioneering work and interesting experiments !
I refer to your web page ever so often.
A post from the past that might be of some help.
I found splitting the signal like a crossover network for a speaker did not sound as good as overlapping the HPF and LPF(this was for a 7 string jazz guitar).
https://www.diystompboxes.com/smfforum/index.php?topic=99697.msg875121#msg875121 (https://www.diystompboxes.com/smfforum/index.php?topic=99697.msg875121#msg875121)
I have a bass big muff deluxe that has a switcheable crossover before the fuzz. I have a feeling though from memory that if you switch in the crossover then only the highs go to the fuzz - the lows go through as clean.
Good article Jack!
How did it sound? The problem with most fuzz boxes is that if you let too much bass in, it get's really "messy".
Roll off lows and it cleans up/gets tight but is then too "thin".
I just built another SD9 and it sounds like there's too much lows going through the overdrive. Very buzzy sounding.
Again, I'll note that differential-clipping can be pursued to different ends. One, as Aron alludes to, is to yield a more pleasing distribution of harmonic content, by either allowing for different bands/ranges of harmonic content to be adjusted in their representation. This is part of the strategy underlying what the TS-9 and derivatives do, as well as the approach adopted by the Rat and Bluesbreaker derivatives, with dual ground legs providing more gain for some parts of the spectrum than others. All of them take note of the fact that the brunt of the signal "lives in the basement", as I like to say, resulting in more clipping for lower strings/notes, unless one compensates by reducing the amplitude of lower notes, prior to clipping.
Jack's approach, that he linked to, does not alter how much a given part of the spectrum clips, but rather how much a part of the additional harmonic content generated ends up in the final audio output. That's not "lesser" in any way, just a particular approach to use of harmonic content; more like harmonics-specific EQ-ing.
The approach adopted by the Anderton Quadrafuzz and the Yamaha MBD-100 is different in that there is no separate post-clip filtering of bands, only tonal adjustment of the aggregated outputs of the individual clipping bands (although Yamaha's Balance control only adjusted for the upper two bands, and allowed the lowest band to be mixed in without any attenuation-control). I don't know what Yamaha's intention was, but Craig states explicitly that a primary objective was to reduce intermodulation. Now, just how many bands are truly required to accomplish that is pretty much an unknown, but Craig settled on 4. I suppose people can feel free to explore more bands, if they wish. I will simply note that pursuing individual clipping within narrower bands also obliges some means of adjusting proximity-to-clip, since individual bands have differing amounts of acoustic energy, requiring adjustment of gain to reach whatever forward voltage is needed.
With the Flexidrive, I stuck with two bands, chiefly because it was simpler and smaller, and allowed for the reciprocal gain/drive pot to be implemented (something that 3 or more bands would not permit). But I also adopted filtering both before and after the clipping point. This provides a sort of blend of the approach adopted by Anderton and Yamaha, and what Jack proposed. I won't say it is "better", just different, and available for folks to explore, and expand on.
We have an entire history and legacy of processing guitar as a sort of monolithic signal, when it comes to adding harmonic content, with occasional digressions. One example that comes to mind is the placement of Uni-Vibes ahead of distorting pedals, such that large segments of the guitar signal are moved away from, and closer to, the clipping threshold, as the pedal modulates. This suggests that there are opportunities for "interesting" sounds via amplitude modulation of individual bands, having their own clipping circuitry.
Quote from: Shoeman on August 03, 2021, 06:22:27 AM
Question for ya. When R-C filters is there a best practice for any of the values? Playing around with the AMZ calc I see that you can make a filter for any typical guitar freq with a wide combination of values. .1 and a 4k vs .022 and an 18k for a 400hz low pass for example. I'd guess this was probably covered in basic audio circuit design 101 but I was absent that day. ;D
+1 what Vivek said about impedances.
Aside from that, I'd add that it's more difficult to get caps in many values (E6 or E12 series if you're lucky) whereas getting resistors in E24 series or better is simple. So it makes sense to start with a cap value in the right ballpark and then adjust the resistor to taste.
Caps have poor tolerance, and PCBs have parasitic capacitance (of several pF or more) so tiny cap value <100pF are definitely better avoided. Large value caps finish up being electrolytics or expensive or large (or all three) so you need to keep the cap values below <1uF so you're in the common range of the sorts of film caps that are good for audio.
For resistors, you've got more scope perhaps, but again, there are practical limits. Large resistors >470K start to produce appreciable amounts of noise, so you want to avoid huge R values too.
Luckily for us, the mid-value-range around nF caps with KOhm resistors produces the audio range we're commonly after, so meeting these practical guidelines is rarely onerous.
HTH
Quote from: amptramp on July 31, 2021, 10:03:32 PM
This may be a little more complicated than it needs to be. The Big Muff overdrives use capacitive coupling through antiparallel diodes in a transistor feedback stage to get isolation of low-frequency signals from the diodes to a greater extent than high-frequency signals.
For another approach, you could use a state variable filter with high, low and midrange frequency outputs and only apply distortion to the midrange. The lows would get too muddy if they were clipped and the highs would get additional unnecessary harmonic content, so if you just apply distortion to the mids, the world becomes a better place.
The Big muff stuff can be used on any opamp (loop) clipper but it almost never is used. I wonder why. flat response at low gain and bigger low response at high gain surely is a dynamic effect.
A quality rather MUFFled under the typical scooped Big Muff tone control.
One of those interesting paths to work on ...if one has time.
Quote from: amptramp on July 31, 2021, 10:03:32 PM
The Big Muff overdrives use capacitive coupling through antiparallel diodes in a transistor feedback stage to get isolation of low-frequency signals from the diodes to a greater extent than high-frequency signals.
Here is a graph of the current in the caps before the antiparallel diodes (BMP Triangle)
(https://i.postimg.cc/jdRGd8S1/BMP.png) (https://postimg.cc/z3PdxFWw)
I need to try this. I have that tube screamer clone I modded with sockets for the diodes. Perfect for this.