Measuring frequency response?

[idlefaction]

Hey all, 

I have this simple booster circuit that I built years ago based on the Dallas Rangemaster, but have tweaked the cap values to taste.  It seems to react with my pickups; on one guitar it sounds very different from others.  With one particular guitar (telecaster, sd pickups) it sounds heavenly!  I've been using it constantly for about four years now.

Was wondering if anyone had any ideas on how to measure the frequency response with the guitar in-circuit?  I tried recording some guitar clean and with the booster in, but couldn't really get from there to any kind of frequency comparison due to lack of software-savviness...

Cheers!

[niftydog]

"measuring" with guitar in circuit... nope. But, "eye balling" it with guitar in circuit is possible although I'm doubtful it would help you much, especially if you're trying to make comparisons between different guitars.

I suppose you could potentially use a spectrum analyser to give you an idea of the frequencys being generated, then compare. But, even then, how do you know if it's the pickups or the impedance match with the booster that's causing the differences!?

Build a buffer so that guitar changes don't affect the booster.

[idlefaction]

I suppose you could potentially use a spectrum analyser to give you an idea of the frequencys being generated, then compare.

Yep, I have some plotted spectrum analyser outputs for clean and boosted, I'm just not sure how to go about turning these into any kind of frequency response of the pedal.

Build a buffer so that guitar changes don't affect the booster.

Sadly I really *like* the way it reacts with one particular guitar, and want to replicate it with all my guitars!  I think trial and error with a parametric EQ might be in order.

[niftydog]

Yep, I have some plotted spectrum analyser outputs for clean and boosted, I'm just not sure how to go about turning these into any kind of frequency response of the pedal.

Well, normally Æ' response is quoted between the -3dB points, but this can be a bit fuzzy, especially when you're trying to look at effected outputs. The ideal response is a flat line between 20hz and 20khz, but when you're looking at filters or any form of EQing then it becomes much harder to know what is "good" or "bad."

So, it's a matter of judging where the majority of the spectrum sits in terms of amplitude, then finding the upper and lower frequencys where the amplitudes drop to 3dB below the "average" amplitude.

But it sounds like you're more interested in what's going on in the middle bit so you can replicate the sound with another guitar. The way to do this would be to print out the different spectrums plots and compare them. You may be able to get the software to draw a "smoothed" line across the tops of the spectrum peaks to give an easier to read representation of the overall response.

But, if it were me, I'd be grabbing a parametric EQ and twiddling till it sound right! There's no measurment device like you own ears!

[Processaurus]

if you were real curious you could play some white noise through your pedal and record that on the computer, there are lots of pc spectrum analysers out there.