The Line 6 DL4 has been called “the most influential pedal of the last 20 years.” The big green box is still found on countless pedalboards worldwide, despite having debuted at the end of the 20th century. With all that success and continued steady sales, why in the world would Line 6 want to make a change? We wondered about that, too. Fortunately, we had a chance to sit down with Eric Klein, the chief product design architect for Line 6, Ampeg and Yamaha Guitar Group. He gave us the backstory, the thought process behind and an inside look at the development of the new—almost the 20th Anniversary—Line 6 DL4 MkII delay pedal.

The HUB: It’s been 23 years since the original DL4 came out. Why update it now? What was the impetus?

Eric Klein: We really wanted to do a DL4 MkII to coincide with the 20th anniversary in 2019. If I remember correctly, it was either [Line 6 co-founder] Marcus Ryle or I who hit the other up in a hallway and said, “Hey, we should do a MkII for the 20th anniversary,” and the other person said, “Yes, let’s do it.” Then, we went to town, and it was designed very, very quickly. The final product definition was done, I think, within a week. I mean, other than the deep meaty stuff—the features, the functionality, all the mods, all that stuff—it was easy. Unfortunately, because of all sorts of things, both in and out of our control, it came out a few years later than we had initially planned. Other projects got in the way—COVID got in the way.

The HUB: What do you think made that initial planning so easy?

EK: I think we were standing on the shoulders of giants, honestly. I mean, the DL4 is a classic. A magazine, I can’t remember exactly which, called it the most influential pedal in the last 20 years. And for me, personally, it was.

A good portion of the work was to make sure that it did the [original] DL4 justice. We needed to make sure that it wasn’t sonically inferior in any way. We didn’t want a single person to say, “Oh, I prefer this from the original DL4.” We wanted everybody to go, “I do like this better. It does more. It sounds better. It’s more sophisticated, and even if I don’t want all of the new features it has, I can treat it exactly like the DL4 that I’ve known for two decades.”

The HUB: The other pedals in that series [MM4, FM4, AM4] did well, but they haven’t had a 20-year shelf life like the DL4. Even with the competitive pedals that have come out looking to capture that market, what do you think makes it so enduring?

EK: A lot of it is the workflow. A lot of it is, admittedly, maybe a bit of nostalgia. Once you “get it”—once you see what we were going for with the DL4—it becomes an indispensable piece of your arsenal. Even when we had some initial problems with the footswitches, people were rebuying them over and over again, because they couldn’t do their sound without a DL4.

In my opinion, the other pedals in the family are a bit more utilitarian. I mean there are a couple cool, interesting sounds in the MM4, and the FM4 is certainly really cool, but delays never go out of style. They’re always at the forefront, whether you’re using them as slapbacks, or whether you’re using weird, crazy, spacey things for ambient textures. They’re always appropriate.

The HUB: Did you feel any sense of intimidation or trepidation designing the successor to such an iconic pedal?

EK: Yeah. I think a little bit. The big thing is I didn’t have to do it alone. As long as I could sleep at night knowing that an existing DL4 user wasn’t going to be upset by some design decision, I felt good. I knew we couldn’t really go wrong from a feature standpoint, because we had a lot to work from. We had a lot of feedback—over two decades—on what to improve and what could improve. We saw what people wanted to see—from the mod community, from web forums, customer emails and from artists, not to mention Line 6 employees. We had a pretty straightforward roadmap on where it needed to go and what it needed to be.

The HUB: As you look at how far the technology has come since the original DL4, what excites you most as far as what that enables you to do as product designers?

EK: It’s funny, in that the products that we’re releasing right now are the least exciting products we’re working on. We’re looking a good 8, 9, 10, 11 years in the future, so we know what work we’ll be able to do then, and we’re already starting to put the seeds together.

The DL4 MkII is based on ARM [Advanced RISC (reduced instruction set computer) Machine], as opposed to SHARC [Super Harvard Architecture Single-Chip Computer]. ARM is a more affordable processor, which allows us to make things more affordable to the masses. But it also lets us do a couple things that we weren’t able to do previously. It doesn’t let you run like six HX blocks simultaneously, or eight, like you can find in HX Stomp. But it’s still really flexible and really affordable. It allows us to go into markets that we haven’t been in for decades. So that’s the big excitement for DL4. Plus, there are a lot of opportunities on ARM that don’t exist for SHARC as well, and we’re looking into those as well.

An angled view of the Line 6 DL4 MkII Delay Pedal

The HUB: What was it like trying to recreate the sonic character of the original with so much more DSP at your disposal? There must have been a desire to say, “We can do this a little bit better, rather than the same,” right? Did that ever enter your mind?

EK: Yeah, and in a couple cases, that is the case where there were obvious sort of negatives to the original sound, just straight noise, for example. We were able to improve things in the modeling realm, too, not just the analog circuitry or the conversion that adds noise. There are modeling components and gain stages in the digital realm that can also add noise, and with better tools, we’re able to minimize that sort of thing.

Something that’s really interesting is that in some cases, it actually takes more DSP to make things sound worse, because the behavior of older technology is more inconsistent and less predictable. We end up having to throw more code at it to emulate that inconsistent behavior, and sometimes hard decisions are made on whether or not it’s worth going down that road. We have to look at it and decide if that inconsistent, unpredictable quality is a sort of “magic” or cool sound that we’re hearing, or is it just annoying?

One example of this is that the original DL4’s mix knob has kind of a screwed-up taper. There’s not a lot of stuff that goes on at the beginning or the end of its travel, but a lot of people will play that like an instrument. You know, they’ll get down while the audio is feeding back, and they’ll work with that mix knob in a very musical way. Well, the day DL4 MkII was released, people came back like, “I hate this taper. What are you guys doing?” And our answer is like, “Well, it’s like the original one.” So, we had to go back and really look at it. It turned out that there were enough comments where we said, “Okay, we’re going back and making that taper more like a modern pedal.” What was interesting was that it was clearly newer guitarists who weren’t used to the original DL4, or older guitarists that don’t remember that about DL4 when they had it years ago, that were complaining.

So, we’re addressing some of those issues. We’re always trying to improve things and trying to predict what people will and won’t like. Generally, we would err on the side of keeping it the same. I can’t remember how many conversations I had where someone said, “Hey, Eric, should we do this or this?” Unless there was an obvious solution the answer was almost always, “Well, let’s just keep it the same.”

The HUB: As you look at changing behaviors of knobs or other aspects that are a little more subjective, have you considered making them switchable settings?

EK: Yeah. I think that is totally appropriate. For this particular one, we have other ideas on how we want to use those global settings. We only have room for 16 global settings, so in this case, we thought there was enough feedback to just make the change.

But, in other cases, absolutely we’d make that a switchable global setting. We’ve done that on Helix products, where we go, “Alright, so you guys want this. We’ll give you this, but if you want it, you have to go into the global setting to turn it on. Then you’ll get what you want.” We want to make it switchable because we don’t want to screw up the functionality for users who are happy with the way it is now.

The HUB: Let’s talk a little bit about the “secret” reverbs. You’ve got some pretty flexible routing, right?

EK: By default, the reverb is not on in any of the factory presets you can access, so they are treated sort of as a secret Easter egg, though most people know about them by now. Most of the presets have the reverb post-delay, but you can move that to be in parallel with the delay or in front of the delay. Because they’re independent of one another and because they have independent knobs, you plug in the expression pedal, move the heel down—which will turn the reverb up and turn the delay down—or you can then go toe down and flip that. This allows you to dynamically blend between the reverb and delay within the same preset, which is very cool.

A rear view of the I/O on the Line 6 DL4 MkII Delay Pedal

The HUB: How deep is the MIDI implementation?

EK: All of the knobs, all of the model selections and all the looper functions are assignable to MIDI CCs. Also, some of the looper functions are even controllable via MIDI Note, so if you’re a keyboardist, you can dedicate an octave of your keyboard to triggering the looper, which makes it really easy to loop your keyboards.

The HUB: What are the most straightforward MIDI integrations a user could use? And on the opposite end of the spectrum, what are the most complicated or “out there” setups?

EK: As I just mentioned, the looper can be controlled by MIDI Notes, which means any electronic drum kit can now take advantage of DL4 MkII. So now, drummers can take advantage of it without having to set up a special loop, or microphones or anything like that. Triggers can now trigger the looper.

The expression pedal input also gets its own CC, and I know it’s like pulling teeth to get people to plug an expression pedal into DL4, but even the original one could do this, and it’s so awesome and inspiring to be able to morph all five knobs. It maybe sounds really hyperbolic, but if you pick the right model, namely like a tape model, and you assign and crank the feedback up on the toe, but drop the time on the toe, you’re now controlling both of those knobs. If it gets too loud, you can back the mix off a little bit on the toe, and now as you’re playing, just play the expression pedal. You can almost play the feedback like a melodic instrument, because it will start self-oscillating at specific pitches. Alternatively, if you’re a keyboardist, you can assign that to the mod wheel or a real-time control knob on the keyboard itself.

I’ve actually made entire ambient pieces, where I use that as a bed. It kind of sounds like a keyboard, but it’s not. It sounds like feedback, but it’s not, and it really is just a guitar through DL4 being controlled by an expression pedal. It’s something that DL4 has been able to do forever, and it’s so fun and interesting and cool. And it can be looped! So, if you have this crazy feedback to drone, then you hit a switch. Now it’s down an octave, and you have this big ugly pad underneath your doom masterpiece. Or you do some weird thing—pop that up an octave, and now you have this feedback to drone that can come in and come out, and then self-oscillate into itself. It just has a personality of its own, and it’s weird to think that’s a delay pedal. Obviously, it’s not uncommon to be able to twist knobs. The old Space Echoes people would get that crazy dub sound. It would sound great. But being able to perform with it live while you’re playing is really a new experience. DL4 was really the first pedal to do that sort of thing—and of course you can do that on the MkII.

The HUB: While we’re still talking loopers, would you mind explaining the key differences between the “classic” looper and the new one?

EK: The classic looper is really sort of a performance looper. It’s extremely immediate, and you treat it more like a musical instrument than like a utilitarian thing, as you might with some dedicated loopers—like multi-track loopers are. For DL4 MkII, we didn’t want to mess with it too much. We wanted to keep the workflow the same, so if somebody owned a DL4 and was intimately familiar with it, we wanted them to be able to sit down with MkII and play a gig without even thinking about it. It had to behave exactly the same way. The only thing they’d need to know is if they wanted to pull up a specific model, like a legacy model, they’d have to hit one button, which is the legacy button. Other than that, that’s the only thing they need to know. Everything else, workflow-wise, is very, very similar. If they want to loop for two minutes, they can do two minutes, but if they happen to put a card in the back, they can loop for hours. And then there are some other sort of “quality of life” improvements, like being able to change delays or change reverbs while the looper is going—things like that.

The HUB:  One other thing that really jumped out when I was digging into the MkII was the different bypass modes. Can you explain the differences from one mode to the other?

EK: By default, it’s traditional DSP bypass, with or without trails. So, what happens is the guitar is converted to digital—like it is on most pedals—and then when you bypass it, it keeps the echoes trailing off. Because the guitar is still in, it’s converted to digital. We also have a true-bypass mode where if you turn it off the trails go away, but the signal goes all the way through in the analog domain, so it doesn’t get converted at all. There’s also a buffered bypass that runs through a buffer, so you can do that as well, and there’s a mode where it bypasses that signal but then the trails continue to go on as well, and you can turn the trails off independently in the global settings.

There’s also a dry through which is an independent parameter. So, you can have it so the dry guitar signal is going in and only the delayed signal is in digital—it’s mixed in with the dry signal with the VCA [Voltage Controlled Amplifier]. So, depending on what mode you’re in, the mix knob is either a digital blend before the dry and the wet, or it’s actually controlling a VCA mix of the analog signal with the digital signal.

The HUB: When it comes into the digital domain, what’s your sample rate and bit depth as far as that conversion and then even the internal processing?

EK: DL4 MkII is 24 bits, 48kHz, which is the same as Helix.

The HUB:  Do you have plans for a deep-dive software editor in the future?

EK: The hardware is certainly capable of doing that, but it really depends on what our users want from us. If it’s something that they’re really loud about, we’re more than happy to give them something like that. Something that has five knobs—well I guess ten knobs if you count the reverbs—may not need an editor. But, yeah, it’s totally within the realm of possibility.

The HUB:  Any major updates coming down the pike in the near future? Do you view firmware updates as incrementally addressing things, or do you envision a future where there could be some major new functionality added?

EK: It’s all up to our end users. We’ve already received some requests for some relatively simple things. 1.01 was released in early July, but that was primarily bug fixes. As far as new features go, we would love DL4 to kind of be a delay pedal for a while. We want it to be a kid.

First and foremost, it’s a guitar pedal. I know that users have really come to expect lots of updates as they’ve seen in Helix land. For DL4 MkII, it really depends. I will say, it’s probably more difficult to do on something like DL4 where the models and functions are silk screened on the top panel. But things like additional global settings, additional tweaks and other things like that are totally within the realm of possibility.

The HUB: Do you have a favorite classic setting, and do you have a favorite new setting?

EK: Both Cosmos. I’m also a big fan of the Euclidean. The ADT is a lot of fun, too. People shouldn’t sleep on that. There’s actually some really great sort of grimy, tape-ish sort of double tracking kind of stuff that really just adds a bit of oomph to your signal, even if you don’t hear the delay. If you keep it really subtle, it adds just a little bit of tape saturation that sounds great.