Misc Waveform "Studies"

[Paul Marossy]

OK, not really studies, but some observations. I didn't take pictures this time, but I checked out a pile of my DIY distortion pedals this evening with my oscilloscope. Here is some of the ones I tested and my observations.

Boutique Fuzz Face - More or less a square wave with the tops and bottoms at a bit of a slope.

Howie's Metal Simplex - Very weird looking waveforms. I haven't seen anything like it before tonight...

AMZ Mini Booster - Same general waveforms as the other pedals I think sound good. Asymmetrical soft clipping was evident, and there wasn't any sharp edges to speak of.

Blue Magic - Another one with waveforms similar to the AMZ Mini Driver, except that there was more effect that could be seen with adjustment of the gain control. Asymmetrical soft clipping was also evident, and the mid boost switch does have a noticeable effect on the CRT, but it doesn't seem to sound that noticeable...

Highway 89 - Another one with good looking curves. Asymmetrical soft clipping in this one, too.

3 Legged Dog - This one also had very good looking waveforms. Nice asymmetrical clipping.

Freddy Fuzz/Black Cat OD-1 clone - I know some of you don't like opamp clipping, but this circuit has some nice asymmetrical clipping going on. That may have to do with some pre-dist/post-dist tone controls that I have added to the circuit. This one really is pretty versatile in practice and it cleans up nice with the guitar volume control.

That's it for now. I'm going to check out another 6 or 8 more in the next day or two.

[petemoore]

my guess is that in many circumstances you can see Fet 'Smoothness'?
 Boutique Fuzz Face - More or less a square wave with the tops and bottoms at a bit of a slope.

Howie's Metal Simplex - Very weird looking waveforms. I haven't seen anything like it before tonight...

AMZ Mini Booster - Same general waveforms as the other pedals I think sound good. Asymmetrical soft clipping was evident, and there wasn't any sharp edges to speak of.

Blue Magic - Another one with waveforms similar to the AMZ Mini Driver, except that there was more effect that could be seen with adjustment of the gain control. Asymmetrical soft clipping was also evident, and the mid boost switch does have a noticeable effect on the CRT, but it doesn't seem to sound that noticeable...

Highway 89 - Another one with good looking curves. Asymmetrical soft clipping in this one, too.

3 Legged Dog - This one also had very good looking waveforms. Nice asymmetrical clipping.

Freddy Fuzz/Black Cat OD-1 clone - I know some of you don't like opamp clipping, but this circuit has some nice asymmetrical clipping going on. That may have to do with some pre-dist/post-dist tone controls that I have added to the circuit. This one really is pretty versatile in practice and it cleans up nice with the guitar volume control.
 That would be my interpretation of the above observations.
 CMOS [3 LEG DOG] didn't get included simply because CMOS has tube like qualities, but I think sounds much different than Discrete Fet's.

[Paul Marossy]

Yeah, I think the ones with FETs or FET/MOSFET combinations have softer clipping characteristics.

I didn't see that much difference with a CMOS based circuit, but they do generally seem to sound a little more "complex".

BTW, I forgot to mention the 1590BB Shaka Tube that I just built. If you look at the picture below, I was told that those humps in the middle of the bottom of the waveform is a second order harmonic. If this is true, than this would explain why this one sounds so good to me - and accounts for the very tube-ish sound. On top of that, it's also got asymmetrical clipping going on, too.

[cd]

It's all in the EQ - if you low pass filter a square wave enough, you end up with a sine wave.  Fuzzes sound trashy, buzzy = lots of clipping, odd harmonics, square wave.  Overdrives gently clip the signal without a lot of change, so what goes in comes out = slightly squashed sine wave.  etc. etc.

[WGTP]

Cool stuff.  Keep it coming.

[bioroids]

Great info.

Please tell us what kind of signals are you feeding the effects with? What happens when you set the tone in flat (if that's possible)?

Luck

Miguel

[Mark Hammer]

Not so much a criticism as a sincere request for more comprehensive examination of waveforms.

As I have badgered on and on about over the last few years, what can appear to be substantial differences between the clipping achieved through pedal A vs B can frequently be simply a result of how much gain is applied in device A vs B and what sort of signal one is feeding them.  Pedal A may seem to be capable of much harsher and robust clipping than Pedal B, but stick a small amount of gain ahead of B to complement what it provides on its own and magically B is able to emulate A.  In some instances, that gap can be closed by merely adjusting the internal gain of B via a simple component value change, or perhaps by changing diode types to alter the clipping threshold.

That is not to say there ARE no differences betwen pedals since the convenience of not having to tack on a booster stage or switch to different pickups represents a true added value for a great many players.  It is important to recognize, though, that "standard" signal measurement conditions for audio devices have always assumed static signal conditions, such as several standard test frequencies at standard amplitudes and harmonic complexities.   Under conditions of a 1khz injected sine wave at 1Vpp, a great many pedals WILL look identical on a scope.  That's not a slag at the measurement reliability or the motives/competence of those who measure in such a manner.  However, it will not provide a rich enough set of conditions to capture what is different about how each circuit "responds" so as to provide a better understanding of what makes them different or similar.

For instance, I suspect many people here would be able to identify a distortion pedal they have used which they would unhesitatingly recommend for single note runs but not for chords, or perhaps for two-note power-chunks on lower strings but not for anything on unwound strings...or chords....or pedals that give majesty and muscle to chords but come off a little wimpy when single notes are picked. A slightly smaller group would likely be able to identify pedals that hold up nicely for distinctly picked notes but don't manage a rapid succession of notes terribly well, or pedals whose desirable sponginess only increases as you throw more notes at it.  Similarly, there will be pedals that hold up well for SC pickups and others that sound terrible unless you feed them a hefty overwound HB signal, and pedals appreciated for their capacity to deliver a consistent degree of sizzle with others valued for the way in which they hold a "reserve supply" of distortion that can be strategically called upon by more aggressive picking.

And on and on.

Then you get to the differential sensitivity across the passband issue so nicely identified by the Tube Screamer and other related devices.  Here is a perfect case of a 1khz/1vpp tone telling a flat out lie about the sound of the pedal, since it is explicitly designed to work against the naturally occurring differences in string to string output in a guitar.  Additionally, every note a guitar produces consists of more than a fundamental, and more importantly, a CHANGE in harmonic emphasis/amplitude over the lifespan of the note.  The filtering in the pedal will turn this into different sorts of "distortion trajectories".

I don't think it is possible to ever completely capture the kinds of real-world circumstances that ALL "normal" guitarists will ever impose on such pedals, but I do think it is possible to expand the range of testing/scoping circumstances investigated so as to yield more elaborate and richer information about what to expect as the nature of the input signal changes from one inspired moment to another.  Scope pictures are certainly a start but the real story is told with more transitory and dynamic information.

[Paul Marossy]

Mark,

I understand what you are saying. Many of the pedals I have looked at with my scope really didn't show much change with frequency - only the frequency changed. So far, the 600Hz sine wave input seems to work fine. I only use that because it is somehow less annoying than 1kHz to me.  

It seems to me that the real story would be told with a spectrum analyzer and maybe varying the input signal in a similar manner to a guitar. Man, I wish I had a spectrum analyzer! I guess I'll have to get one next...

[niftydog]

I'd suggest that you go the PC based spec an route. A simple interface box, hooked up to a semi decent audio card, appropriate software and bobs your uncle!

[Paul Marossy]

Yeah, that makes sense, I forgot that those programs also have a spectrum analyzer built into them...  :oops:

Do you have any suggestions for what program to use?

[petemoore]

So...you CAN draw certain conclusions about waveform studies, or observations..
  There's no substitute for various [good / worst case] scenarios when it comes to pedal testing. These don't do much without the use of an amp, and of course the guitar.
 The scope does give an interesting perspective on different clippers waveforms, it's fun analyzing the shapes even if conclusions are non-conclusive much of the time
 Some of these circuits exhibit interesting information in the waveshapes.
 I like to see them..
 So..with that...who has a frequency analyzer?>is there a digital model of a FA...
 I don't really know but guess it allows viewing waveshapes of more complex content?

[niftydog]

there's plenty of software!
interesting free freq analyser software with source code available (C++)

one's that have been recommended to me;

freeware stuff;

Oscilloscope

SoundArb

Digital Sound Generator

Shareware;

Osci, WaveGen, AudioTester

Analyzer

Interface kits can be made, I thought you could get a kit of this, but I can't find it.

[Paul Marossy]

Thanks niftydog. I downloaded a few of those to try out.  
But, I need something to interface my D.U.T. to the soundcard, right? I don't suppose you could dig up a schematic for that, could you? I have a feeling that a kit might be a lot easier. Or, even just buying that gizmo in the last link...

[Arno van der Heijden]

I don't suppose you could dig up a schematic for that, could you?

Rob Strand designed such a device a few years back. I cannot find it right now, but I must have it somewhere. I will dig it up.

[Arno van der Heijden]

Pssssst!!!

http://images.google.nl/imgres?imgurl=http://us1.webpublications.com.au/static/images/articles/i305/30518_14mg.jpg&imgrefurl=http://www.siliconchip.com.au/cms/A_30518/article.html&h=619&w=1026&sz=51&tbnid=jYcXuoTajP8J:&tbnh=90&tbnw=149&start=44&prev=/images%3Fq%3D30518*%26start%3D40%26hl%3Dnl%26lr%3D%26ie%3DUTF-8%26sa%3DN

:twisted:

[markusw]

See also http://www.dazyweblabs.com/shannonsoft/page3.html for other free oscis.... I connect to my laptop via a Tascam US-122 interface and it works quite fine.

Markus

[Paul Marossy]

Thanks Arno!

[Arno van der Heijden]

You're welcome Paul!

This is the thread I was talking about:
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=723

I also found the Rob Strand's diagram on my computer. It consists of a coupling cap, a couple of resistors and two back to back diodes.

BTW, once you manage to view that Silicon Chip page without the Google frames, you can read all articles on that site!!!!!!! Including this one:
http://www.siliconchip.com.au/cms/A_30329/article.html

[Athin]

I use baudline
www.baudline.com
a fft is better than looking @ waves.... (edit) IMHO o'course  :wink:

[Paul Marossy]

Unfortunately, it looks as though that schematic by Rob Strand is not available anymore...