Bass Distortion with an adjustable Crossover?

[stickninja]

So this is my first post here.  I am a sound engineer, and have just recently gotten into building small electronic projects.  I was asked by a friend of mine if it was possible to build a bass distortion pedal that had an adjustable crossover.  Meaning dry signal underneath the threshold passes through, and any signal above the threshold is distorted.  now, I have searched the forum and come accross topics about crossover distortion, but i'm not they are describing what i'm looking for, or if they are, I am just thoroughly confused.   So ultimatly I guess my question is, is this possible? has anyone ever done something like this?  Thanks in advance for the help.  I'm looking forward to learning from everyone here.

[petemoore]

So this is my first post here.
  Hello.
  I am a sound engineer
  I'll reserve judgement 'till later on this one, so am I [lol].
  and have just recently gotten into building small electronic projects.
  The best fun someone who has never gotten into SE Projects can have.
   I was asked by a friend of mine if it was possible to build a bass distortion pedal that had an adjustable crossover. 
  I'll bet he means split the signal input into 2 frequency bands [lower/higher] 
  Meaning dry signal underneath the threshold passes through, and any signal above the threshold is distorted.
  Depending on what threshold means...but sounds like description of vanilla distorter.
  now, I have searched the forum and come  accross topics about crossover distortion, but i'm not they are describing what i'm looking for, or if they are, I am just thoroughly confused.
  You will probably only find descriptions/circuits of distortion events that takes place as the wave inverts to opposite phase and crosses over from + to -...push pull tube amp bias talk + some small signal circuits which create 'wiggles' in the wave, near bias center line...a separate, dissimilar to what I think you want..project for another day IOW.
  So ultimatly I guess my question is, is this possible?
  If you thought of it probably yes.
has anyone ever done something like this? 
  I'll try to put a solid secure handle on what 'this' is below.
  Thanks in advance for the help.
  1T for askin', 1 T for thanking !
  I'm looking forward to learning from everyone here.
  Welcome !
 

[petemoore]

  Block diagram typed:
  < means buffer-splitter, in this case creating two frequency bands [HF, LF], in the case of the low pass filter, by passively removing everything above say 1khz [arbitrary figure for discusting], then boosting what is left, the 'bass boosts' misnomer is explained, you can only remove which equals cut = volume drop [fortunately boost is also possible].
  > Means 2 into 1 mixer.
  - means subrated from signal.
  LF means low frequency, HF = High Frequency.
 
                   HP Filter,+Processes
  PICKUP<                                   > on to neXt thing [amp?[
                   LP Filter, +Processes
   Example:
  Have or make 'amazing' amplifiers and speakers and cabinets, [or work with small signal extensively?]
  Plug the guitar through an active crossover.
  Connect something that can respond to VeryLF's to the LF output, vary the HP filter setting so the HF's can be heard sweeping down to where there's only muddy sound.
  Connect somthing that can respond to mid-hi-and highs to the High Frequency output ofthe crossover [and not the LF output], vary the LP filter sweep knob and hear the lows then mids disappearing as it's swept up.
  Spend 8 days one week trying different cabinets and rooms while twisting, setting, listening, adjust cabinet and cabinet position...for best results.
  ...otherwise...
  Splitting the signal, see Elliot sound projects.
  Perhaps treat the bass part to only enough boost to bring it back to 'balance with the HF part, consider compression for louder-overall, less demanding on the bass speaker response. Low frequency clipping may sound like 'buzzy-clicking' becuase the time constants between clipping events is so long and the clipping event is so short.
  Fuzz or distortion on the HF portion can thicken sound by adding harmonic content, and is more like tuning a dirtbox for guitar.
  It's all theory on my part...if I started up the bass/amp more I'd probably try something like that.
  At any rate, crossover distortion probably isn't going to get anything except how to bias a PP tube amp and how to make Xover Distortion [middle of signal wave distorted..which is in opposition to the approach taken...that 99% of distorters which clip signal peaks]...not that there's anything wrong with it perse', I'd work with signal peak clipping circuits first.

[auden100]

There's a couple of projects that could be adapted to suit your needs.

From what I've read about the Quadrafuzz, that might be something you'd be interested in, though perhaps overkill for you purposes.
http://www.paia.com/proddetail.asp?prod=6720K

Perhaps a little simpler, I'm reminded of the OmniDrive. Some redesigning might be in order, such as routing the LP filter over the clean signal as opposed to the distorted one, and removing the octave section if preferred. Unfortunately, it's good, but the greatest sounding distortion.
http://www.hollis.co.uk/john/circuits.html

It might be easier to make a splitter/blender box with an integrated hi/low pass filters, one for each channel. Then you could plug in whatever distortion you wanted. You could start with the Bass Paralooper and add some filtering from there.
http://www.moosapotamus.net/THINGS/paraloop/paralooperSCH.gif

[petemoore]

  Study filters, parametric for instance [GEO]...perhaps a couple of these and a split-blend ?
  Elliot Sound projects/articles.
  Power supply voltage for such a project might do better at greater than 9v.
  Running everything after the splitter as a channel [all the way through the associated HF/LF amps and speakers...requires HF/LF speakers/amps, can offer rewards that 2 split-frequencies-processed-then-mixed into 1 fullrange system doesn't offer.
  The 'big advantage' [lol] is that the simple 2 into 1 mixer isn't needed.

[Mike Burgundy]

Also interesting: Mark Hammer's Gruntbox. I'm sure there's stuff on the forum on that, or Mark'll chip in
It's basically what you specify - highpass line with distortion, lowpass line without. May need some tweaking, but it's a cool start, and very doable.  Taking it a step further would involve (tunable) 2nd or 3rd order butterworth LP and HP filters, and the amount of electronics involved just isn't justified by the end result for a distortion box  IMHO.
hih

[Mark Hammer]

There are two general approaches to what you seek, or rather what your friend seeks.

One is to insert some frequency division prior to distortion, and then combine the signals such that the clipping is applied only to some portions of the signal, and the output consists of the unaffected signal, and the other part that is clipped.

The other would be to split the signal, apply clipping to one copy of it, and then filter the clipped portion such that the harmonic content to be added to the unmodified signal would be selective.

Either way, the objective of distortions optimized for bass is to permit the fundamental to be heard very clearly, and have the distortion simply add a sort of "burr" to the tone.  Much like any effect intended for bass guitar, there is an overarching need to retain the clear audibility of the fundamental so as to hold the foundation solidly in a way that permits other instruments to wander without losing a sense of the key.  That's why choruses and flangers aimed at bass try to keep the notches out of the lower region, and the autowahs preferred by bassists are generally lowpass filters  that don't mess with the bottom.

A couple of years back, I briefly tinkered with something I called the Gruntbox ( http://hammer.ampage.org/files/Gruntbox.zip ).  I won't profess it to be a divinely inspired gift to bass players, but the basic premise is to combine dry and clipped signals, and the circuit diagram gives a kind of play-by-play description of what it is doing at each step.  That may give you some ideas of what you might be able to dream up yourself.  If you go here - http://hammer.ampage.org/ - and scroll down, you'll see a description of the sound clip included in the zipfile.

Addendum: Almost forgot.  The variable crossover part.  My guess is that the opnly part that really needs to be variable is the highpass filter for the signal going to the clipping.  Whatever filter is used for the clean side can befixed and fairly shallow.  A dual-ganged pot and a 2-pole highpass outght to be enough for siphoning off any portion to be clipped, though.  I mean, it's only rock and roll, right?

[moosapotamus]

I was asked by a friend of mine if it was possible to build a bass distortion pedal that had an adjustable crossover.  Meaning dry signal underneath the threshold passes through, and any signal above the threshold is distorted.

I did some experiments with that exact idea a couple of years ago. The drawback of using a crossover is that the gap/overlap between the hi pass and lo pass is fixed, and what I found was that there was really just one sweet spot, so the variable crossover didn't really provide much flexibility in terms of being able to dial in a range of different sounds. I found that having two separate filters in parallel, one hi pass for the disto and the other lo pass for the clean, each with it's own independently adjustable cutoff frequency, was way more flexible and allowed for creating a lot more different, cooler sounds compared to a crossover with a single control for setting the crossover frequency. In fact, a hi pass and a lo pass filter in parallel makes for some pretty flexible tone shaping all on it's own with just a clean bass sound with no disto at all.

~ Charlie

[Mark Hammer]

Charlie!  Great to hear from the moose himself!!

[runmikeyrun]

I was just going to say... where you been Moose?  Your projects are awesome, are you "back"?  This is the first post i've seen by you in a long time.

[moosapotamus]

Thanks, guys!
Been kinda busy, changing jobs, starting up a new business, yadda yadda...
Also been playing a lot more than building.
... but, I'm still around.

~ Charlie

[edvard]

One of the best bass sounds I ever got was when I ran a Ricky with a shorted pickup into a RIAA phono preamp.
The pickup sounded tinny and weak so I had to run it through my old 4-track to bump the signal up (which caused some dirt) then used the preamp to jack up the bass end.

Since then I've toyed with the idea of making this idea into a pedal (minus the busted pickup) by feeding a hi-passed signal into a distortion and then boosting the low end at the other side, using the same filter point for both; maybe the same as the original idea (RIAA curve).
That way, the bass end would be too low-volume to overwhelm the distortion stage (a common drawback when distorting bass, I've found) and then boosting the bass afterward restores the original relative levels but the distortion harmonics more evenly spread.
Does that make sense?

[12Bass]

Using a crossover for bass distortion is not a new idea.  Nor is the technique of rolling of the low frequencies before distortion and adding them back in afterward.  Bassists like Chris Squire, John Entwistle, Geddy Lee, Doug Pinnick, and Tom Petersson, have used various methods to split their signals so as to distort the higher frequencies while keeping the lows solid and relatively unaffected.  

Some years ago, whilst pursing the "ultimate bass distortion sound", I purchased a Yamaha PB-1 preamp, largely because it has a built-in crossover which allows you to independently adjust the level and frequency of both the highpass and lowpass.  On a whim I also bought an Ashdown Bass Drive Plus, which is a bass overdrive pedal which has a preset crossover frequency, but allows separate adjustment of drive for high and low bands, with a blend at the output; the idea is cool, even if the execution doesn't sound that great.....  

[ashcat_lt]

It's strange, I just "designed" and built a pedal for my bassist that's exactly the same conceptually as the Gruntbox.

Mine splits the signal into two copies after an input buffer.  One copy hits what is basically a Rat with gain all the way up, with the output cap too small.  The other copy gets a little clean gain and then hits a variable lowpass and then they're mixed together.  I've added TRS insert jacks at the split, so there's an effects loop before the distortion and another on the clean side.

I just hacked it together from other peoples circuits (I'd not seen the Gruntbox previous) and had to make do with values of components I had laying around, but I'll put a schematic in a while.

[Mark Hammer]

It's like pyramids showing up in Egypt and Mexico at the same time in history!!

Actually, nothing particular innovative on my part with the Gruntbox.  "Divide and conquer" is a time-honoured strategy for effectively tackling some types of audio processing issues, so no great surprise that it pops into other people's heads too.

I'll toss a coin to see whether this falls into the "great minds think alike" bin, or the "fools seldom differ" bin. 

[Mike Burgundy]

Edvard:makes a lot of sense. This is actually used in many, many pedals for guitar - guitar low end can also get muddy or farty when clipped too much - reducing bass *before* clipping works to retain decent low-end without fartiness, and for guitar that's often enough. For bass it might be a very good idea to incorporate some kind of LP or shelving EQ to push the lows more after clipping. Many here agree that pre- and post-clipping eq is more important for a distortomegagaintronfuzzthingy than the actual way of clipping.
Go for it!

[edvard]

Hehe...
I'll name it "GloRIAA"