Author: ericharbauer

When I first got my Helix, it was right about the time that the firmware dropped with the Litigator model.  That update was actually what pushed me over the edge to buy Helix in the first place.  I’m a huge fan of the Dumble style tone, have been for years.  I own a Fuchs ODS 50 HRM, which is simply a fantastic amp, and one of the most well respected “D style” amps on the market today.  So when I opened up the Litigator model, I was a bit thrown off.  There was no individual controls over the gain stages. My Fuchs, being true to the dumble circuit has an input gain control, and a second gain control for the OD stage. There were no deep, bright, or Jazz/Rock switches. there was no gain boost, no mid boost, and seemingly, no overdrive channel at all. I was perplexed as to how I was going to make this thing sound like a dumble.

Now please don’t get me wrong.  It sounds fantastic, and even gets close to my beloved Fuchs, ….but not quite. So for the past several months I’ve been on a mission to “tonematch” my Fuchs, set the way I like it, in my Helix.  

For reference..Here’s the settings I used for this entire project.  So the question is basically where do we start? How do we set up a test rig for a real amp?  How do we even test it?

For starters, I often run my amps with my Helix using what I call the 2 cable method.  I honestly don’t know if thats the right name, but its the one I use.  Basically I put the entire amp in an fx loop on Helix, using a reactive loadbox, so its 2 paths send and return, which is why I use the term 2CM.  Its send from helix to amp input, amp output to Two Notes Torpedo Captor, and then DI out back to Helix.  Works like a charm.  Drop it in my favorite patch, add a Litigator, set a footswitch so I can A/B them. I dial my Fuchs in the way I like it, Get the litigator close and away we go.  So I start by doing a sweep of the clean channel and see the EQ curve and compare it to the Litigator, make a few tweaks and we get this.

Here we have The Fuchs in green and the Litigator in Blue. As we can see from 100hz to around 5k they’re virtually identical.  I’ve got them pretty close EQ wise. The low end actually mimics the Fuchs OD channel pretty well, so I’m betting that the litigator is based mainly on the OD channel of a D style amp. Also, for whatever reason it appears to me that some kind of high cut or something was applied to the amp model.  In the end this ends up being something you really just cant fix. To a certain extent some EQ can be applied to it to bring some of that back, but its hard to make something from nothing.  I’m not going to worry about it too much right now.  Time to check the waveforms.

Helix is on the left.  This is at 83hz with a -26db test tone.

Now they’re virtually identical here, but that’s a pretty quiet signal. lets bump it up to -18db and see what happens.

Again Helix is on the left 83hz but this time at -18db

As you can see the Fuchs is producing asymmetrical waveforms as it gets pushed, and Helix isn’t. This pretty much happens throughout the entire spectrum, and the Fuchs becomes more sensitive to it as we go up in pitch.

Here’s the Fuchs’ waveforms at -26db (below) for reference.

As we can see when it’s not pushed its pretty symmetric, and un-distorted right through the entire spectrum.  The helix behaves the same way when not pushed. So since this is the clean channel were after, it’s likely not that big a deal, we won’t be pushing it too hard to play cleanly.  Plus the waves are still rounded, and will sound pretty smooth.  It ain’t perfect, but it’ll have to do, plus I really can’t tell the difference between the two when I play them.  Its that close.  All the fabulous dynamics the Fuchs is known for are right there for the taking. Here’s a sound sample.

 

So now lets go on to that drive channel. lets see how close we can get it with only one gain knob.  Lets start with the waveforms this time.

Here we are at 83hz Helix is on the left.

Both are pretty clean here.  Nice sine waves.

Now at 200Hz . Helix on left

As we can see the Fuchs is behaving differently here. It’s doing the asymmetric wave thing again, while helix is pretty much un-distorted.

Here we are at 500hz. Helix (left)

Both are distorting here, and Helix is actually starting to perform more like the Fuchs. They’re both getting pointy on the ends, and moving towards becoming more similar.

Here we are at 1khz Helix (left) Fuchs (right)

They’re virtually identical from here on up, Its pretty remarkable actually.

1500hz Helix (Left) Fuchs (right)

2khz Helix (left)

So basically from 500hz on up the 2 amps are virtually identical. As to why they’re different below 500hz, I’m not really sure.  Best guess is different power tubes.  Dumbles, Fuchs’ Bludotones, 2 Rocks all come with different power section options, and there’s a decent chance that’s what’s behind the variation, But again, I’m not exactly sure.

Now lets move on to EQ because we know we’re going to have some work to do here.  Virtually all of the changes in controls that I’ve made so far were to make the waveforms match up. So we’re likely way off.

Yep, we’re way off.  Time for EQ So I play around with the eq for a bit, I finally make an IR using match EQ and get them where I want them.  Now I try the patch, and they sound really similar, but no way you would call them identical.  The Helix has way less gain, its way less compressed, and just not nearly as glorious as my Fuchs. At this point I’m pretty convinced that the lack of an input gain control is limiting the Helix model from really shining.  So I take a Litigator preamp block and put it in front of the amp and play around.  Its definitely better, but still not enough gain, even with the preamp block dimed it doesn’t get loud enough to compress the Litigator amp model. Its not even close, and remember my settings from up there, both of my input gain controls are at maybe 10:00, nowhere near approaching what the Fuchs is capable of producing.  So I scratch that idea and add a gain block, and bingo, that really wakes it up.  A little fiddling, and a switch to a kinky boost, adjust some EQ we get this.

But how does it sound?  Meh…  Don’t get me wrong, It’s close, really close but there’s 2 problems.  First the high end roll off of the helix model is apparent.  Its just a little bit of sizzle, but it’s notably absent. Second the Fuchs has this mid thing…  It’s almost like a cocked wah.  The Kinky Boost helped bunches, but it seems to me to be just too broad of a boost.  Too much lower frequencies, and its just too mushy and compressed.  An important thing to realize.  D style amps have a Gain Boost on a foot switch.   This boost drops the tone stack entirely out of the circuit and sends the signal directly from the first gain stage to the overdrive stage.  Basically it cascades clean into overdrive, and gives you controls for both stages.  Lets see what the boost looks like on the clean channel where its not compressing, and we can get a good idea.Fuchs ODS clean channel Boosted (blue) vs Normal (Green)

So it looks like we need to add some mids in front of the amp.  The high end stuff doesn’t matter because the Litigator model cuts that off anyway. Lets put an EQ in front of our Litigator and see what we come up with.

Here’s the EQ curve and the Eq settings I used instead of the Kinky boost. Lets give it a go on the clean channel to see how it sounds before we hit the front of the drive channel. Here’s a sound sample.

I’m pretty darn impressed.  It sounds pretty darn close on the clean side.  Now lets see what we get with the overdrive channel.

So how does it sound?  …Well Its glorious, Absolutely Glorious. Its not exactly perfect on the overdrive channel. The Fuchs compresses more, and there’s that high end roll of thing. Small issues, but issues nonetheless, and I hear them and miss them, but at the end of the day I’d be pretty happy with this patch in the absence of my Fuchs.

 

Here’s the link to the patch on CustomTone

 

https://line6.com/customtone/tone/3730963/

 

 

 

Thats all for today.

 

E

A quick look at the distortion characteristics of a Mesa Boogie Mark V in IIc+ mode set how John Petrucci set his Mark V in a comparison demo for Mesa. All frequencies are listed in the tone generator bar.

Ok, so I saw this post on the Helix FB group the other day that referred me to the fractal forum, where I read a post about Aliasing…  WTF…. no -like seriously -WTF was the OP talking about?

https://www.facebook.com/groups/line6helixusergroup/search/?query=Han%20Uman

Now, if he was talking about Aliens… well hell I get that, those buggers show up in my research all the time, and I can make them dance like this when I crank up the ripple Control…

 

 

 

Well it turns out the OP was Cliff the owner of fractal, and he wasn’t talking about aliens but, “Aliasing”…  What the hell is that?  Fractal has a new unit coming out, and it’s expensive, very expensive.  Gotta be a marketing thing right?  They’ve gotta differentiate themselves from the plebs for sure.  But honestly – I have no idea.  So half an hour later and half a dozen googles later I come up with a basic (very basic) idea of what foldover aliasing actually is.  Apparently, sampled Audio can only record tones at 1/2 the sampling rate, and for some reason this is named the nyquist frequency.  This means that standard CD sampling rates, which is 44.1khz, can reproduce frequencies up to 22khz, which is nyquist for cd quality audio.  Well that’s above human hearing, so who cares right?  Well apparently sounds (harmonics and the like) will “fold back” (I think of this as bounce back but whatever) around  the nyquist frequency and appear back in the noise floor of the lower frequency bands, where they are called aliens… I mean aliases.   Aliases tend to be particularly egregious because they fold over a frequency that is not harmonically related to the fundamental frequency, but rather related to the sample rate.  Thus they appear as anharmonic peaks in the noise floor.

Ok… this exhausts my rudimentary knowledge of this subject….. Headache… Excedrin….

If you must dive deeper here are some resources.

https://en.wikipedia.org/wiki/Aliasing

https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2015/09/04/aliasing-in-adcs-not-all-signals-are-what-they-appear-to-be

Try Google….  I’m done with the aliens.

So here’s Cliff’s original post from the Fractal forum. I suspect it to be the new AX III vs Helix, it apparently demonstrates superior anti aliasing performance of his newest unit. Let’s Investigate shall we?

Let’s break down what the he says….

1. “I believe that a target goal for a “high-gain” amp should be a minimum of 60 dB of what I call “Signal-to-Peak-Aliasing”.”
2. “…so any aliasing above the threshold of audibility (60 dB) reduces clarity and definition.”
3.  “Analog amps don’t alias…”
4. Aliasing is particularly nasty because it’s harmonically unrelated to, and can occur at frequencies well away from, the desired frequencies (and, hence, is not masked by our perceptual process).

First let’s delve into the whole “60db of  signal to aliasing ratio” .  I think of this as signal to noise ratio, but since we’re talking about the aliasing component of the noise floor, I’ll roll with that terminology.  Now I saw some discussion in the thread about how the 60db number, and was bunk because 60 db was only relevant at 30hz and the real number at 10khz was closer to 18db…  Ok so half an hour later and half a dozen googles later I came to a few conclusions….

For the record, I’m no audiologist, and I don’t care for reading doctoral dissertations on The Threshold of Audibility.  Note that term, Threshold of Audibility.  Not threshold of hearing which is entirely different.  So let’s take a look.

Here is a chart for threshold of hearing (I like charts better than tables of numbers) And as the FB post I read indicated, it shows that it indeed is 60 db at 30 hz and approximately 18db at 10khz.  There are however 2 problems with this.  First, we’re talking about the frequency of the alias and not the frequency of excitation (input frequency) so at the alias frequency (lets use 5khz) it’s closer to zero… which would mean…what exactly? I have no idea… Why? mainly because of the second problem — our old friend (no not the aliens) Threshold of Audibility which refers to the human ability to hear one sound in the presence of another sound.  More precisely our ability to hear an alias in the presence of the fundamental frequency. Here’s the most relevant chart I could find on the subject. 

Now, I see the minus -60db on the left side, and I see the entire guitar frequency across the bottom….. I’m sure that the frequency of the alias vs the fundamental frequency makes a difference, as does the volume of the fundamental etc…

If you must dive deeper here’s some resources.

http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/earcrv.html

https://www.sfu.ca/sonic-studio/handbook/Threshold_of_Hearing.html

Try google …Because at this point I’m done with doctoral theses on hearing aid design.

Headache… Excedrin…. you get the picture.

So since it’s just a number someone picked to be their standard… I’ll roll with it for now. We’re just going to be looking at what is actually there and reporting it. I’ll let the hearing aid doctors debate the merits of the 60db signal to alias ratio.

Ok time to look under the hood.  First up… Fuchs ods50 vs Line 6 Litigator.

Here are the settings on the Fuchs

Fuchs is just there to compare…. (’cause real amps don’t alias)

So lets see 10khz first.  Fuchs (green) and Helix (blue)

Ok so this looks pretty close… Shockingly close actually.  I see my Fundamental frequency at 10khz, and its first harmonic at 20khz.  A couple other spikes but they all match up, and as we know real amps don’t alias.   The 2 spikes at 120 and 240 on the Fuchs graph are from the power supply which I was able to dial out with the ripple control on Helix… so far so good. Up next… 11khz

Ok, so they both get messy here, but the Helix still consistently produces that spike at 5200 hz and at 3900 hz like the last graph. Now for 9khz

Ok! Well Both amps clearly like 9khz better.  But what the hell are those spikes at 4.305khz and 13.28khz?  No idea.  Aliases? Aliens?  maybe…… to be honest I used the Helix to switch in and out the Fuchs, maybe the sample rate of Helix made a difference..  Idk .

Headache… Excedrin…. Rinse… Repeat….

New test gear arrives tomorrow… More soon.

New Gear Day!!!!

My dentist loves sweetwater as much as I do.

Anyway, I spent the better part of 2 days getting this rig dialed in.  I’m not a Windows guy, plus the laptop I was using was in as far over its head as I was… anyway a quick bribe to my youngest son (who just got a gaming pc for christmas) and I had a totally workable laptop.  It just needed a total clean wipe a windows reinstall, and all my software moved over… Thus the better part of 2 days.  But in the interim I still had my old unit going.  so I continued to conduct tests, figuring I’ll just update the screenshots…

Here are some posts from those tests.

This is a line 6 helix Cali IV Lead vs my Mesa Boogie Mark V in mark 4 mode.

And this is the Line 6 Litigator vs my Fuchs ODS 50 HRM.

Everything looks ok.  I’m not loving the shape of the graph, it was a sweep file I just chopped up in logic and looped, and I wasn’t particularly happy with the result, but both amps received the same signal, and since we’re looking at the differences, not the shape of the graph, it seemed relevant to me.  So I put em up on facebook to show how close the line 6 was to a “real” amp.

Right about now The laptop has finished loading windows.  Time for  my interrogation by Cortana.

Headache… Excedrin….  It’s becoming a theme…

Cortana seems satisfied with my answers… So let’s get back to it. Load up the software and away we go!

First up lets look back at that litigator and see if there’s any differences from the old gear. 

Here’s that 9k test tone.  This time no aliases.  It turns out all digital gear creates aliases, and my old (cheap) test gear was no exception.  So either my test gear wasn’t able to accurately produce the desired frequency, or it interpreted incorrectly on the return.  Either way, the Aliens are gone… for now.  Now lets run that sweep test from logic and see what we get.

 

 

 

Ok so the presumption here is that those lines going up and down to the left of the sweep frequency are aliases, but there’s so much noise.  It is at this point I realize that almost anything I do with the computer causes a noise spike.  Even as simple a thing as hitting Printscreen to take a screenshot, so runnung an audio file is killing the performance. So I’m betting that it’s processor noise, or video card noise, but it’s apparently coming from within my pc and not elsewhere.  Maybe a signal generator will work.  But TrueRTA doesn’t support sweeps, and plus it’s noisy when I first turn on a test tone. So a couple googles later I find an online tone generator.  Ok lets see what we get.  First up . Helix with no blocks installed… a blank path.  Lets see how just the Hardware performs.

 

 

 

Looks good.  No sign of Aliens here…  Just a steady sweep from 9-12k and a nice clean graph.  Now lets put a litigator in the path and see what we get.

 

 

 

Holy crap!  WTF is that???   …Unexpected to say the least.   Is this the rare and seldom seen sweeping Aliens..  Uh I mean Aliasing caused by harmonics folding back over the Nyquist frequency and appearing in the noise floor of the amp model…?? Unexpected, but only because I’ve seen no sign of it up till now. (It’s amazing what a bit of new gear will do) …Anyway, assuming it is aliasing, let’s see what the vaunted “signal to aliasing” number is.   At the 4-5 second range we have the loudest harmonic fold thru at -64db at that point the fundamental frequency is at -10db so that’s 44db “signal-to-peak-aliasing” or 16 db shy of Cliff’s stated minimum. Well now I guess we may as well try my amp again, and lets see what we get. Cause remember real amps don’t alias…

 

 

 

Holy Crap!  THE ALIENS HAVE INFESTED MY FUCHS!!!!

Well that was even more unexpected than the last test that came up weird and stuff…  with harmonic waves sweeping all over the place… Real amps cant alias, so what is this I’m seeing? Is my new rig incapable of measuring this stuff?

Headache… Excedrin….  walk away… get some sleep.

So the next day I’m thinking about this test, and reading up on antialiasing filters, (yes thats actually a thing), and I started to realize that every A/D converter is susceptible to aliasing, and better ones will have some sort of anti-aliasing filter.  Since anti aliasing filters are just basically low/high pass filters, maybe I overloaded my A/D converter, and compressed the signal so much the filter couldn’t differentiate between aliases and non aliases.  Ok so I redo the test on the Fuchs, carefully calibrating my test rig, and boom.

 

The aliens are gone!  A bit of further testing reveals that if I push that input signal over +31dB of gain thats where the filter starts to break down.  So now that I know the limitations of my gear I can finally run that test and see what the heck Cliff is talking about.

 

The graph above is that same sweep as I subjected My Fuchs to, 9-12k sine wave.  This time the test was conducted with the “peak hold” function on,  the same way Cliff apparently performed his when he compared his model of a high gain amp to the helix model.

Placater (green), SLO lead OD (purple), Cali Rectifire (Light yellow),  Cali IV Lead (Orange),  ANGL Meteor (Lt Blue), PV Panama (dark blue)

Signal path for Helix tests: Toshiba laptop>Audient ID4>Helix>Id4>Laptop

Signal path for amp tests:  Toshiba laptop>Audient ID4>Fuchs ODS50 hrm>Torpedo captor DI out>Id4>Laptop

Lastly, a few notes about all of this.  This test is brutal, and probably somewhat unrealistic. First, using the peak hold function creates a graph that is a bit misleading, as it only maps the worst performance at each frequency interval, and not the average.  Which is important because not all frequencies are stimulated at the same time. Second Amps do produce lots of harmonics, but this is really loud at 9-11k, frequencies that can never be the fundamental because they are beyond the guitar’s range. Just for an example the amp that Cliff used produces harmonics that are 12db lower at 9khz and 18db lower at 11khz.  Point is the fundamental frequency will always be significantly louder than any of this.

At this point I really need to get my hands on an Axe Fx unit to compare to.  If you are interested in seeing that test happen you can contribute here.

https://www.gofundme.com/gainstaging-geekery-fund-for-gear

That’s all for tonight,

E

 

 

 

 

 

 

 

 

 

 

Ok so today I want to do a quick run through the Timmy.  Its a pretty versatile OD that With its Bass and Treble cuts can get a wide array of tones.  I just want to write up a quick Post to go through the different modes of the pedal and what they do.

Here’s a little bit of the circuit.  I’m not interested in posting schematics so i’ll just post a snippet showing the switching and clipping diodes.  Essentially we see an opamp (triangle) with a feedback loop (pretty much everything in the green rectabgle above the triangle.  we have 2 diodes in series going in each direction, allowing only one half of the waveform to pass thru each set.  The interesting part of this circuit is the two additional diodes on switches.  They can be added in and out of the circuit to create some asymetric clipping and some Interesting results.  Lets see shall we?

 

Thats all for today

E

Another effective way to mimic turning a Mic off axis in Helix is with an IR. It can be especially useful if you are already using the split path for something else, or you are running dual cabs and cant run dual split blocks.

Here’s a link to where you can find these.

 

https://thefriendlygearfreaks.com/threads/3-irs-for-mic-axis-rotatation.5920/

 

Ok so a quick post on Old reliable….  The SM57 regularly spotted pressed up against the grill cloth in venues the world over.  It can be a bit bright, But when mixed with other mics and/or placed off axis, It can be a very useful tool. Here’s a bit of relevant data on the SM57 model Found in the line 6 Helix.

Factory frequency response chart

As Measured in helix (below)

Below is a Graph of an SM57 on (green) vs. off axis (blue) as we see the crossover range is 1000hz to 2100hz  My tests at 1600hz yielded quite acceptable results. So 1600 is a good starting point and adjust to taste.  +3db bass and -1.8 highs.

 

SM57 Split crossover technique 30 degree off axis recommendations.

Crossover 1100hz to 2100hz

Low +3db

High -1.8db

 

If you’re not sure what this is all about here’s the article where I discuss this technique. A little something on Mic Distance and Axis with an sm57

And Here’s the article where I explain how I take these measurements. Mics . Don’t like em? Delete em..

E