Interesting Distortion EQ analysis

[WGTP]

http://www.thestompbox.net/ViewArticle.aspx?ArticleID=32

Shows EQ's of modeled distortions.  It doesn't get into the harmonic content, but demonstrates how important EQ is to different sounding units.   

[johngreene]

I'm not sure it is really providing much in the way of useful information though. He doesn't really say what he is using to scan the device but because it is having trouble at the lower frequencies I would guess that the device is being swept at a different rate than the output is being scanned. As opposed to using a tracking generator. So you see artfacts of harmonics generated by the limiting of the lower frequencies in the higher frequency response. Measuring the frequency response of a device that is limiting the signal is problematic for other reasons as well. The unit can have a lot more 'gain' at some frequencies than others but because of the limiting nature of the device under test, the response will look pretty much flat.

If it was me, I'd have the horizontal scale be log base 10 and not octaves, I would reduce the input signal level to be less than what causes the signal to be limited or clipped to make the frequency response measurement. I would then take several measurements at single or two-tone frequencies while driving the unit into it's normal operating range. To measure harmonics as WGTP mentions.  I think this would paint a significantly different, but clearer picture of the differences between all the units tested.

IMHO.

--john

[WGTP]

I was taking a pretty "gross" veiw of it.  The curves were fairly close to stereotypes I've developed from hearing and building and reading about these things.  The "stack" and R-man curves were interesting in that I have been EQing things lately by using a BMP tonestack after several stages of distortion to boost the low/mid freq. (with a 4-5db dip around 800Hz) and then rolling of the lows thru the distortion by using a small input cap and/or smaller cap to ground from the FBL.  With an open back combo amp with lots of mid's (PV) this seems to work fairly well in getting closer to the EVHish Brown sound (not that that is the ultimate goal, but who doesn't like a big warm {not flabby}bottom with sparkly highs).  That balanced with the right amount of bite (and some Mosfet clipping ).   

[R.G.]

I posted this recipe years ago. It's still a good one.

Take two seven band EQ pedals. Put one in front of your distortion pedal. Put the other after the distortion pedal. Adjust to taste.

A boost in the front EQ causes more distortion in that frequency band, a cut causes less. A boost in the back EQ pedal boosts distortion products in that band, a cut cuts distortion products in that band.

If you're picky about tone, you can spend entire days playing with this three-pedal setup.

[brett]

Hi

The unit can have a lot more 'gain' at some frequencies than others but because of the limiting nature of the device under test, the response will look pretty much flat.

Isn't the frequency response a plot of gain vs frequency?
Ifso, and the response looks "pretty much flat", how can some frequencies have high gain and not others?
What is "limiting nature" ?
cheers

[WGTP]

As John said, there are probably better ways to do it.  I'm guessing, each line is 10db?*^#?

R.G. you were correct as usual.  I lose sleep at night thinking we build too many different distortions when some EQ changes are the main difference between them.  I guess some of us just need to keep our hands busy, or maybe it is theraputic.

Probably what most of us need in a pedal, is a nice distortion with a few options and a 7 band EQ, but what would we do with ourselves then?  Practive scales?  Learn digital recording?  Is that supposed to be fun?  (I don't really mind the scales that much)   

[johngreene]

Hi

The unit can have a lot more 'gain' at some frequencies than others but because of the limiting nature of the device under test, the response will look pretty much flat.

Isn't the frequency response a plot of gain vs frequency?
Ifso, and the response looks "pretty much flat", how can some frequencies have high gain and not others?
What is "limiting nature" ?
cheers

"Limiting nature" is basically headroom. As soon as a signal hits the limiting range, due to diodes or whatever, the 'level' of the signal will no longer increase. It has been limited. At that point the amount of 'gain' will determine the slope of the signal's transition between the upper limiting point and the lower. This will not show in a 'level' vs frequency plot which is what we are talking about. What I proposed is a way to measure 'gain' vs. frequency.

--john

[puretube]

I love that "dip" around 296Hz in the

Muff Boss GT6

curve,
and the one in the RAT Boss GT6 around 834Hz...

[johngreene]

I love that "dip" around 296Hz in the

Muff Boss GT6

curve,
and the one in the RAT Boss GT6 around 834Hz...

Commonly known as the "Elton Mod".

or "Letterman Mod".


Or "Madonna Mod".

[WGTP]

Yeah, that dip will be tough to do with a couple of resistors and caps.   

Has anyone seen a comparison like this with fewer issues?