Beginners Guitar/Bass Pedal Review: DigiTech Dirty Robot

So this is a new thing that I want to start doing and I figured this is as good a platform as any for it. Lately I’ve been getting into guitar/bass effects pedals in a big way. I’m going to start reviewing them here as well as posting some soundbites from them to showcase their abilities. I’ll only be reviewing pedals that I own, because as I’ve learned over the past few months,  it takes a while to get to know each pedal’s individual range, characteristics, and pros and cons. Now, I know there are a lot of pedal reviews out there, so I’m going to angle this towards beginners and explain some of the stuff that I may not have known going into owning each pedal. I’m also not going to rate any of the pedals or features on any scale like 1-5 stars, or 0-10 scale, partially because the pedals I have, I love and so you’d see a lot of high ratings, and partially because I want this to be about you learning as much as you can about each pedal before you decide to make a purchase. I don’t believe star ratings are the best way to do that. It may take longer to read a review like mine, but I promise I will do my best to give you the information you need to make an informed purchase.

So that being said, I’m going to start with DigiTech’s Dirty Robot Synth Pedal for Guitar and Bass. It looks like this:


Image Credit: DigiTech by Harman

Upfront Statement: I am not being paid by anyone to post this review, nor have I or am I planning to receive any gifts because of it. I am reviewing purely to put my opinion on this pedal out there.

Baseline (not going for the pun there): The Dirty Robot packs in a powerful synth engine along with a vocoder-style vocal formant filter into a small, well built stompbox that won’t destroy your checking account. If you’re looking for that “next step” in tone, that guitarist or bassist “it factor,” this may be what you’re looking for.

Notes: It should be noted that not only does the Dirty Robot work for Bass Guitar, it was designed to work seamlessly with both bass and six string guitars. I’ve used it in recording for both bass and guitar. While I will mostly be coming at this review from the standpoint of a guitarist, bassists should know that this pedal covers them in an excellent way. Also, I am recording directly through the Dirty Robot to a Behringer U-Phoria UMC204HD audio interface, so there will never be any other modifications to the soundbites I record, nor will there be any equalization alteration that may come from going through an amp. What you here is my Ibanez Artcore guitar, and in some soundbites my Dean bass guitar, being only altered by the Dirty Robot. Also, I’m playing with the “Mix” all the way up, so that you can hear the Dirty Robot at its most powerful, but the mix knob allows you to go from “heavy synth” to “synth backed by guitar” to “guitar backed by synth” and everything in between. You can even set the mix so there’s no synth sound, although I’m not entirely sure why you’d do that, but hey, you’re smarter than me.

Price: One DigiTech’s website, it’s listed at $187, however you can typically find it new on Amazon or eBay for around $150 with more savings if you’re willing to get a floor model or other like new model.

Overview (I will go into more detail about most of these points so if you’re looking just for detail and explanation, you can skip this part): The DigiTech Dirty Robot is built like a f#@king tank. Its chassis (case) is made of a very durable metal, as are all the knobs and the footswitch. Of the pedals I own, it’s by far the one that’s built to last. I’ve been using the Dirty Robot in a studio setting, but I have complete confidence that you could take it into some really rugged gigging conditions and it would hardly even show cosmetic wear. It’s true bypass, which I know gets floated around a lot, but it’s an incredibly handy feature. If you’re not really sure what that means, it gives you the ability to turn the Dirty Robot on and off with the flick of a footswitch, but specifically in the off position, not only is there zero signal interference or loss, you don’t even need the pedal to be powered for the signal to pass through. True bypass makes it incredibly easy to kick on the Dirty Robot when you need it, without having to worry about it screwing up your tone when it’s off. Stereo ins and outs give you a range of possibilities as far as how to integrate it into your pedal system. It’s true stereo, too, which means you could theoretically have two instrument inputs and it would keep them separate for unique output sounds. This is just one of the many possibilities, obviously, you could also have a dry signal in one input and a distorted signal in another, then put one input into an effects loop while keeping the other unaltered. It has three concentric knobs, which means they’re stacked so you really get two knobs in one location, which is incredibly handy for reasons we’ll get into. The fourth knob is a free flowing 360-degree Drift knob that allows you to combine octave, sub, and square wave voicings to really get the most out of the pedal. The Dirty Robot also features a “Mod Wheel” vibrato function when you use the footswitch in its momentary capacity, which I’ll show you a little later. This allows for some great textures to the synth voicing. To cap it off, what makes this pedal truly transcendent is the ability to switch between voicings. Voice one gives you a more classic, 80’s style synth sound, while voice two is a vocal formant filter with variable range, which means it emulates a vocoder or talk box, going from a throaty growl to a robotic “yeah” or “eye” with sensitivity based on your playing dynamics and the sensitivity knob. So. That was quite an earful… or eyeful, I guess. Let’s break it down and I’ll do my best to show you why this pedal has become my personal favorite over the last two months I’ve gotten to know it.


1.) VOICE 1 (CLASSIC SYNTH): The classic synth voice in its own right, with all the available controls (technically 7 controls in 4 knobs), makes this pedal worth the roughly $150 price tag (which is small compared to other synth pedals, though I know it’s still a lot for many of you reading this). While I’m not selling you this pedal, and I’m certainly not getting paid to talk about it, what I would like to do is show you why that $150 investment is well worth the money. It has already found its way into several songs that I’m recording for a future album release, and undeniably makes those songs better and more interesting. Money is hard to come by for me, so it was a big decision to get this pedal (which, full disclosure, I got from a DigiTech Authorized Dealer as a “like new” item for $115). I don’t have the money to be buying pedals that are only good for one thing and one thing only, which is why you’ll see in my later reviews, I trend towards multi-effects pedals. The Dirty Robot essentially is a multi-effects pedal, and even just focusing on Voice 1, I’ll show you why:

1a.) Varying Synth Sounds with the Start/Stop knob: One of the coolest features on the Dirty robot is the concentric (stacked) Start and Stop knob. As I alluded to earlier, this knob is biggest reason the Dirty Robot has the range and variability that it boasts. In voice 1, which is what we’re talking about right now, the start/stop knob dictates the frequencies at which the filter sweep starts and stops. The reason the concentric (stacked) knobs are so helpful here, is that you can automatically see what direction the filter sweep is going and how broad of a range it has, instead of having to look between two knobs to figure that out.

This may be hard to understand from the written word, so I’m going to give you a clip of what it sounds like first when the start knob is set to the lowest it can go and the stop knob is set to the highest it can go (the time knob which controls how long the sweep lasts for will be set to max, and the sensitivity will be set to noon or straight up/half way):

As you can hear, the sweep is very distinctive and starts off at a low frequency, rising to a high, more distinctly synth frequency at the end. So this is showing you the full frequency range of the filter sweep while making that sweep as slow as it can possibly be. I’ve used this in recording for bass guitar so that a simple repetition of one note tuns into a sweeping bass synth, and for my friends on the bass guitar, I’ll show you what that sounds like here. The start/stop knob is in the exact same position it was for the last clip, I’ve just turned the sensitivity to its lowest setting, all the way to the left, so that it’s harder to trigger the filter sweep:

That’s playing, obviously, a very pedestrian bassline, where I’m repeating one note for each sweep, two notes in the whole clip, but the Dirty Robot turns that from boring bass-as-usual to a kind of otherworldly sweeping bass synth. It’s incredible what you can do with this device on bass guitar. I know I’m not doing bassists justice because I’m mainly a guitarist, but you can see there that as I noted earlier, it works seamlessly with bass. It’s not a pedal that just happens to work with bass, it was designed so that you can plug in a bass without changing any of the settings and pick up where you left off. Also, because it’s true stereo, if you’re a band on a budget and want to use the dirty robot for guitar and bass at the same time, you can do that. You can plug bass into one input and guitar into another and then maybe slap some reverb or delay on the guitar and play the bass as is and those two signals will be completely separate from each other, meaning you don’t have to buy two of these to use in one song (although hey, the more the merrier).

Okay so now that I’ve shown you some bass, and the low to high sweep, I’ll show you what it sounds like with the start knob at the highest frequency and the stop knob at the lowest frequency (with the same time/sensitivity settings), so that you’re getting exactly the same sweep just reversed from going low to high to going high to low:

So you can hear the versatility just in those two sound clips, just flipping the settings on one knob of one voice. I would show you all the unique sounds you can come up with just by altering the start/stop knob in various ways, but I’m going to stop myself before I get carried away. But the main thing to note is that the Start/Stop knobs give you versatility in voice 1, from the classic synth tones of the high-frequency range, to the swelling bass tones of the low-frequency range there’s a world of possibilities there.

1b.) Varying synth sounds with the Time/Sensitivity Knob: Another concentric (stacked) knob that adds a huge variation to what you can do with this pedal. The most obvious changes come with the Time function, which changes how many seconds/milliseconds it takes for the filter sweep to go from “Start” to “Stop.” But there’s a beautiful nuance with the Sensitivity function. If you’re familiar with auto-wahs, it’s the same concept, it uses your playing dynamics to start the filter sweep. On the far left, low end of the sensitivity knob, you have to hit the strings really hard to start that sweep, on the far right, high end of the sensitivity knob, it becomes so sensitive that even residual vibrations can trigger the sweep.

I’ll show you what I’m talking about, because an audio track is worth a million words (inflation), starting with variations to the time knob. Now, by setting the start/stop knobs as far apart as possible and putting the time to as low as possible you get some seriously funky laser-gun/Paul McCartney-Wonderful-Christmastime sounds, but those can border on the cheesy, so for this track I’m keeping the time to the lowest setting, but I’m bringing the “stop” knob up to about noon so it’s not such a drastic sweep in such a little time, but you still get that kind of space-age ray-gun vibe:

Maybe not the most subtle sound, but I’m sure you can see in the difference between that and the previous two soundbites how much range and versatility the time function gives you. Those previous two clips with both set to maximum sweep time, so I don’t need to show you that again, and this is the extreme on the other end, but I would be doing you a disservice if I didn’t show you something in between those two. So here I’ll set the time to about noon, and leave the start knob at highest frequency/far right while turning the stop knob to about 10 o’clock, so just left of mid-frequency/noon:

1c.) Give life to your tone with your own natural playing dynamics with the Sensitivity knob:

I’ve mentioned the sensitivity knob before, and explained what it does, and I’m not gonna spend a whole lot more time on it here, but I do want to talk about its capabilities in voice one fora second. When the sensitivity is low, and you’re hitting the strings softly, not triggering the filter sweep, the Dirty Robot will give you the tone you select as your Stop frequency (at least that’s what I’ve been able to ascertain). Another cool feature is that it’s not an all-or-nothing feature. It’s not like it either starts the sweep or it doesn’t. At times when I’m playing with the sensitivity on low, and hitting the strings with medium power, it will give me a shorter sweep that starts at about the middle of the start/stop range. That’s pretty f#@king sweet if you ask me. I’ve tried several auto-wahs and none of them have that capability. What this does is gives you the ability to just play, and the sensitivity will pick up the sweep along with your natural playing dynamics. It’s an incredibly advanced and nuanced knob, which I don’t know that I can show you as well as I can tell you, but as with most parameters on the Dirty Robot, this is a feature that has the power to completely transform the tone you get from the pedal just by the subtle tweak of a knob.

2.) VOICE 2 (VOCODER STYLE VOCAL FORMANT FILTER): Voice 2 is where I think you really get a boom for your buck. If you’re not familiar with what a vocal formant filter is, think auto-wah, or cry-baby wah pedals for that matter, but instead of just being able to make that “wah” sound that they’re named after, they can make a whole range of vowel sounds. They’re similar to a vocoder or talk box, although admittedly not quite as versatile as they don’t have the ability to mimic what you’re doing with your voice, but I tend to think they’re more usable because you don’t have to use a microphone or hassle with the long tube of a talk box. This is where DigiTech really outdid themselves, because they could have created a wonderful synth pedal with just voice 1, but they went the extra mile to give you something you would normally pay hundreds of dollars for on its own. That’s not an exaggeration. Vocal Formant filters are not very common. The most common one I’ve seen online is the Stereo Talking Machine by Electro-Harmonix, which retails for about $220 by itself. EHX also has a Vocal Formant expression pedal for about $100, but it doesn’t have near the versatility of either the Dirty Robot or the Talking Machine. Now, I’m not knocking EHX here, they make what look like some incredible pedals, but the main reason I chose to buy the Dirty Robot was that I was interested in vocal formant filters and also interested in synth emulators. So my choice was to spend upwards of $400, which I didn’t have, getting each of those individually, or spending $115-150 and getting both in the same package. It was really a no brainer from there. The Dirty Robot is a steal for all the effects power that you’re getting in one pedal.

2a.) Vocal Formant Range: The Dirty Robot boasts an impressive range of at least 8 distinct vowel sounds (with the character of those vowel sounds changing as you move the “start” knob. It achieves this through the start/stop knob, which in voice two becomes the range selector for the vocal formant filter. The start knob changes between four different vowel sounds, and the stop knob gives you the ability to reverse the vowel sound to create essentially a new one when you turn it past the noon position. For this I’m going to give you one sound bite where I go through all the vocal formant sounds. Some of them are more distinct than others, but they all bring a unique characteristic to the Dirty Robot. So what I’ll do in this soundbite is go left to right on the “start” knob, and for each vowel sound, i’ll show you the initial sound, and then immediately following, the reversed sound. It should go something like this (and these are approximations so give me a little leeway): way -> yow -> yeah -> eye -> oo-aa -> aa-oo -> ow-uh -> oo

As you can see, some of them “like yeah/eye are more distinct and some of them are more subtle. This gives you a huge range of possibilities with this voice. Because you don’t always want your vocal formant filter to be incredibly distinct, sometimes you’re looking for that kind of indescribable throaty growl, which is what the last two give you. And like I said, these are all one placement of the filter. There is a range for how “yeah” sounds, just like there is a range for how all of these sound. Up front, it’s a very obvious feature, but they manage to pack it with nuance which is what I think guitarists and bassists alike will love.

2b.) Adjusting the time for the vocal formant filter to match your playing: For that last clip I had the time at almost 3 o’clock, but just like in voice 1 how time can completely change the sound of the filter sweep, it can greatly impact how the vocal formant filter sounds, and you can use that to your advantage when you know how fast or slow you want to play. For example, you might consider a low time setting if you want to solo and you want that vowel sound to be pronounced with every note you play (which would also require high sensitivity), or if you’re playing a slower song with sweeping power chords, you might want to extend that vocal formant time so it covers the whole note you’re playing. Now, the Dirty Robot does not have a tap tempo feature for time, so you will end up approximating the time a bit, but I’ve found that the time knob is incredibly intuitive and easy to manipulate based on the situation. So for this audio clip I have it on the “yeah” voicing because that’s my personal favorite, and since you’ve already heard what it can sound like at 3 o’clock, I’ll set it first to 9 o’clock, not quite all the way down but close, and then to a nice mid range at noon.

2c.) Let your playing dynamics do the work on the vocal formant: As with voice one, the sensitivity knob is an incredibly nuanced function on voice 2. The kicker on voice 2, however, and this is a huge part of why I love the pedal, is that when the vocal formant filter isn’t being triggered, you get straight up, classic higher-frequency synth sounds. The reason I love this feature so much is it allows you to pick softly for a synth sound, and then when you really want to take things up to the next level, you pick harder to get that vowel sound out of it. There’s a million and one applications for this, and like I said in the last part I think I can explain it better than I can show it, but it gives you the range to make every note you play a vocal note, or just a select bunch of notes. And as an added bonus, if you turn the sensitivity to its lowest setting, you get a classic synth tone without any sweep, which can also be helpful.

3.) Features for Both Voices

3a.) Add character to your sound with the drift, mix, and mod knobs: Some of the more nuanced knobs on this pedal are the 360-degree drift knob, and the mix and mod knobs. The mix is the most straightforward: it controls how much original guitar or bass signal is in the output. You can go from having all original signal and no synth sound, to all synth sound and no original signal, which is what I’ve been using here. I tend to prefer the mix to either be at noon or full blast, because I’ve never been one for subtlety, but as I’ve mentioned earlier, dialing it back to maybe 9 or 10 o’clock gives you a great subtle sound of a synthesizer kind of “following” your guitar work. So for people who have listened to the clips here and said “I like that, but that’s way over the top for my music,” no worries! DigiTech has you covered. Introduce just a little bit of synth or vocal formant to your guitar signal and get that subtle “it factor” you might be looking for. The mod knob is more nuanced, and isn’t something that I could demonstrate very well on audio, but according to Digitech it adds a Chorus effect to the output. It’s subtle, but it can make a big difference. The way I think of this is that it affects how “thick” your synth sound is. with the chorus off, you get a thinner, more delicate sound, but with it turned to its max position, as it is in all of the above clips, it adds a punch to your sound while giving it that slight chorus waver on held notes. Finally the drift knob has the potential to drastically alter your sound, although admittedly it’s the knob I know least about so you might not want to quote me specifically on what it does. My understanding, though, is that it varies the waveform of your signal with three positions: Square Wave, Octave, and Sub. because it’s a 360-degree knob, you can use one of those, or any combination of two of them. While I can’t say I know exactly what a square wave is, I can tell you that it gives you a more traditional synth sound. The features I really love, however, are the Octave and Sub positions. If you’re familiar with Octave pedals, this basically does the same thing, which means again, you’re getting more boom for your buck. If you’re not familiar with Octave pedals, they do what they say, which is add a sound one octave below the sound you’re playing, and usually they have the capability of adding a sub-octave which is two octaves below what you’re playing. So if you’re playing guitar, this can have the effect of a bass guitar playing right along with every note you play, even ones that bass guitars wouldn’t be able to play. I’ve had the Drift knob set right between the Octave and Sub knobs for today, except for the bass clip which was set to square wave, which means I’m getting one octave below and two octaves below. I find that this really fills out the sound of the Dirty Robot, making it a more complete pedal that fills up space, but again, if you want something thinner and more subtle, they have the square wave for you which will give you that thinner tone.

3b.) Momentary Vibrato Function: This is another one of the coolest functions on the dirty robot, and something that I’ll show in in my last audio clip. This feature kicks in a strong vibrato (altering the pitch of the synth sound up and down in a wave) when you hold the footswitch. So not only does the footswitch serve as an excellent and easy to use on/off switch, it also allows you to take your synth sound up a notch, emulating the “mod wheel” that is found on most keyboard style synthesizers. For this clip I’ll play without the vibrato at first in the “yeah” voicing of voice 2, and then I’ll kick in the vibrato so you can clearly hear the difference:

So just another awesome piece of ammunition that comes with the Dirty Robot Pedal.

Bottom Line: You are not going to be able to find a pedal that does the things the Dirty Robot can do for the money. It’s a high-performance variable synth engine, a vocoder style vocal formant filter, with octave, chorus, and vibrato effects built into an incredibly well built and well designed unit. And it doesn’t hurt that it looks f#@king awesome. Doesn’t take up much space on your pedalboard and allows you to introduce sounds you can’t even approximate without spending at least $400-500. If you’re an adventurous guitarist or bassist, I would recommend marking this as a “high priority.”


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