Taming highs

[strungout]

Oy.

What ways are there to make highs cause less ear bleeds? My fender amp has very sharp highs with the distortion circuits I've been making, but on the amp's own distortion, they're softer. The problem is the filters I've been using to roll-off or shelve the highs (at around 2.5-5kHz) does that, but also makes the sound muddy, or muffled, which takes away some crisp-ness. I've read somewhere on here that Craig Anderton made a circuit that distorted a few freq bands seperately, so I was gonna try that (highs and lows), and mix em back together after filtering. Maybe that would give me more control over that sharpness I'm getting. Anyone have any insight or other ways to soften the highs?

Thnx.

[gez]

You can try using active filters with a sharper 'knee', these won't sound so muddy.  Plenty of text books go into the details (Sallen-Key filters are a good place to start).

Edit.  Actually, just google 'Sallen-Key', there's a ton of info.

[gez]

PS  Using an equaliser after your pedals is an easy way to get results.

[mindwave_21]

Possibly some sort of compressor would do it for you (I don't know how much you wanr cut off though).  If you want to try, you could always adjust the pickup screws on the higher string set lower (further from the string).

[R.G.]

Read "The Guitar Effects FAQ" at GEO. Among the other generally good advice in there is the admonition to use a multiband EQ both before and after your distortion. You would not *believe* the difference this makes without hearing. it.

The pedal you're mentioning from Anderton is the "Quadrafuzz". There are schemos, and kits available from PAIA.

By the way, you don't want a shelving treble cut. You want a "goes down forever" treble cut. The spectrum of distortion products that are made by a clipper go out a long ways and the higher the harmonic, the harsher the sound.

[brett]

Hi.  I'm not surprised that cutting at 2.5kHz to 5kHz sounds a bit "flat".  Try cutoff freqs of 6kHz to 10kHz.  For me, most of the ear-bleeding stuff is quite high (~10kHz??).

cheers

[strungout]

Thnx for the replies. I am going to build a parametric eq to use behind/infront of my circuits, but I want to be able to soften the highs in the pedal itself. I've summarily heard of the Sallen-key topo, I'll check it out further.

Well, I got a few things to try out

Ciao.

[Mark Hammer]

To add to what RG noted, one of the difficulties of distortions is that they add harmonics of whatever harmonic content you fed them in the first place.  As such, achieving a "rounder" sound means taking more assertive action to make sure that stuff out beynd 5khz is not as audible.  

We tend to overlook the use of multi-pole filters, and advantages of planning out filtering sensibly so that fizz does not accumulate in cascaded-drive-stage devices.  A single-pole filter will, indeed, roll off "forever" at the rate of 6db less for every octave you go up, but that still lets fizz through, albeit at a lower amplitude.  An additional stage will roll off at 12db/octave resulting in much less fizz content.  A steeper rolloff also means one can afford to set the rolloff frequency a little higher, because you don't need to start rolling off way down just to be sure the objectionable high stuff is really gone.

Consider the humble Tube Screamer.  It has a rolloff cap in the feedback loop of the first stage.  It has a fixed 1-pole LP filter immediately after the clipping stage, and THEN it has a tone control to roll off more top end.  So, 3-steps/stages of lowpass filtering.  No wonder it has a rounder more vocal sound, even when shrieking.

You will note that the BMP also has multiple filter caps throughout its multiple stages to tame strident fizz.

Tell us a bit about where your distortion is coming from, and I'll see if I can suggest suitable points of intervention.

[brett]

Mark H makes an excellent point about multi-pole filters.  There's a world of difference between 1 and 2 poles.  On a couple of effects, I've used the simple pot+cap filter shown on the DIY mods page, PLUS a fixed filter (nominally set at about 10kHz, if I remember).  Nice steep rolloff, with some control.

Perhaps the place for an extra 1-pole filter is at the input.  Lots of effects use a 470pF to 1nF cap to ground before doing anything else.  Might be worth a try.

cheers

[Brian Marshall]

that is a little trick i did on the stupid box


a low pass on the input, and a low pass on the output.  it actually ended up being pretty effective, and simplified the circuit a bit, because i didnt have to use a bleeder cap as well to tame radio frequencies.

brian

[Ed G.]

In the evolution of the BSIAB II, I had tacked onk a double-pole filter I lifted from the schem of the Prof. Tweed on the end of the circuit, right after the BMP tone stack. I thought it was redundant, but I liked the sound, I could turn up the tone knob and get clearer highs without the excessive 'fizzies'.

Mark's eloquent validated what I was hearing. Got to hand it to him, he's got the technical knowledge to know what's going on, yet can describe it to those less technically adept.
Jake's Blue Magic design adds a single pole filter after his variable tone control also.

I had tried with other circuits to increase the size of the cap in tone controls, which only made the circuit sound soft and mushy, losing the attack. I think the use of multi-pole filters should be considered in the crafting of any good distortion device where it's needed to shave off the objectionable, harsh overtones while retaining the character and tone of the circuit.

[strungout]

This is what I'm working with right now:



From left to right, Gain, Tone, volume.

I set out to better my Strong Gout, but I've gotten way off, so, I'll get back to it later and call this my filter learning/experimental phase.

So, I added a lowpass at the input of the circuit (already had a highpass from my last circuit - check the Strong Gout thread). The rest is pretty generic. I tried green LED see what they would do, and they do good Nice and crunchy. I tried changing alot of values in the two opamp stages, but wasn't satisfied. So, now I'm trying stuff after. I'm not sure if there's much difference between taking the signal from both a lug and the wiper of the tone pot, or only from the wiper? I should have time today to try out a few of the suggestions.

Am I right to think that a tone knob (let's say first order lowpass) is sorta like a "shader", in that, as you turn the knob, you "pull out" a progressively more opaque veil over the affected frequencies, the most opaque part being at the starting point frequency?

Ugh, gotta cut the grass. The other one. Ciao.

[strungout]

Ok, so: Cutting highs at 6 to 10kHz didn't do much but very slightly reduce fizz. My pain is really under 4kHz. I googled Sallen-key, but couldn't find anything that laid it out simple enough for me to understand how to calculate everything... As for the quadrafuzz type circuit, I summarily tried it, but I'll spend more time on it in a few.

Two things happened: One, I added another variable lowpass behind the one after my second distortion stage, making it a second order, thought I'm not sure if and how much the first knob affects the range of the second lowpass:



The first one allows for alot of bass without getting muddy, like listening to music with cotton in your ears, and the second pot cuts away the fizz.
Two, this got me closer to what I want, made me realize I WANT (at least some) fizz and that making the bass louder was maybe the answer I'm looking for. With louder bass, I can keep the volume low enough on the pedal to keep the highs under control, and if I need a higher volume, it means I'm far from my amp so.

Ciao.

[cb]

I like this topic - I think about it all the time - how to reduce the earbleeding hi's while still retaining some hi end. My experience is that the harsh hi frequencies live around 2kHz. Put a graphic eq after your pedal and before the amp, leave everything flat, then start backing off the 2K band (or whatever's closest on your eq pedal) - I think you'll be surprised. Also - to my ears - above ~8kHz are the sweet "hi-fi" hi's. Single coil pickups have a lot of energy up there - pump up the 8K-10K range and your humbuckers will sound a *little* more like single coils - but I digress...

[gez]

I googled Sallen-key, but couldn't find anything that laid it out simple enough for me to understand how to calculate everything

The formula is the bog-standard 1/2piRC (0.16/RC).  Just use two equal value stop resistors to set the upper limit and a dual-gang pot to vary  the cut-off frequency (cut-off is lowered as resistance increases).  The two caps should also be of the same value (though you'll see more elaborate, multi-pole designs with different values sometimes).

Although there's some loss through the RC network, if you slap one at the output of some overdrives (ones which have a large output swing and aren't clamped by clipping diodes)  there's a danger of op-amp clipping (which you may or may not want), so you might have to attenuate the signal driving the filter (number of ways of doing this, what works best depends upon the circuit).

What you've drawn isn't that far off what you need to do.  Salen-Key type filters push the knee of the filter higher so that you get steeper roll-off.  It allows you cut a lot of the high frequency content without muddying everything up.

[strungout]

Oy.

Well, after a few other filter try outs, I settled on this:

I can get the freakin earbleeding highs, if I want, but can also get rid of em without the sound getting farty or palm-muting getting soggy. There's a big volume loss when you play with the high and mid cut, which can be offset somewhat with the blend pot, but the pedal has alot of volume in the first place. I got some annoying hum with my wallwart, but I'm putting the blame on it being a cheap one, have to try a better one. The 10k resistor in the first opamp's FB loop can be ommitted. I put it there cause the hum was giving me this bad octave effect :p.

Any comment is welcome. Thnx to everyone who posted here to help .

Ciao.

[Lonestarjohnny]

Helloooooo, your guitar has a tone pot, turn it into a blender and then you can have it both way's, not as elaborate, but purely functional.
JD

[strungout]

But, AHA!, my guitar's tone pots (squire strat - switched the mid pup tone to the bridge) are my fart mode knobs

[Lonestarjohnny]

You Youngen's know to much, LOL !, Back when I was doin my Neanderthol Rock I figured I just had 3 volume knob's, and that's what I did use them for as the years clicked on by, as the first volume pot wore out i moved it back as a tone pot and moved the unused tone pot up as my new volume, We played so loud you never even worried about E.Q., I know it's a lot different now with smaller gig's, more intimate setting's, so tone is where it's at, Carry on and Ignore me, I'll go back in my Cave now,  :lol:  :lol:
JD

[strungout]

I think I misunderstood what you meant :p

Actually when I said "original signal", I meant the one as it came out of clipping stage, blendinig it back with the signal that went through the two lowpass.