The Mattoverse Warble Swell Echo tells you what it’s all about right there in its name. I appreciate this plain-spoken approach to describing a delay pedal. No tricks, just a delay pedal that warbles and swells. Yet within those simple functions—modulation for the warbling and oscillating feedback for the swells—are worlds of tones fit for deep exploration.The original Warble Swell Echo fulfilled the functional promise of its name by offering a delay circuit with controllable modulation and footswitch-enabled oscillating feedback. In the time since its release, Mattoverse refined the waveform function found on their Inflection Point and Just a Phase pedals, which gives those stomps more varied modulation control. By adding that function to the MkII, they’ve extended its controllability and dosed it with added woozy goodness.Memorex VibesThe basic delay settings on the Warble Swell Echo MkII are controlled by simple time and repeat controls. Just playing with the delay sans modulation, I was already impressed. Though the delay line is digital, it has a warm vintage voice that reminds me of my favorite BBD delays, like the vintage MXR Analog Delay or the Moog MF Delay. And I knew the Warble Swell and I were going to get along as soon as I found myself vibing on Les Paul-style tape-echo sounds and riffs from Neil Young’s Dead Man.Warble controls add modulation to the delay signal via rate, depth, and waveform knobs. Each of these settings are interactive, so it takes time to get to know how they communicate. And some settings are bold while others are subtle. But the learning curve for the Warble Swell isn’t too steep. From the jump, I dug the high rate/medium depth settings with the sine waveform, which is a subtle sound, but set my delayed sound distinctly apart from my dry signal. And even at generous mix settings, I could maintain a clear clean tone amid the slightly warped delay.On the flipside, I was stoked when I found the pitch-bending sounds at low rate/high depth with the square waveform. This setting drove me to explore wetter mixes, which reminded me of the overplayed cassette dubs of warped vinyl that I listened to in middle school. Cranking the time knob to higher levels—starting around 2 o’clock—causes the signal to degrade further, taking the warped-cassette feel to more gleefully broken extremes.I knew the Warble Swell and I were going to get along as soon as I found myself vibing on Les Paul-style tape-echo sounds.All’s Swell that Swells WellThe Mattoverse’s swell functionality is simple and intuitive. Holding down the righthand momentary footswitch causes the delay repeats to feed back. And where you set the swell knob at the center of the pedal determines how quickly that wave of feedback reaches its crest (turning the knob clockwise creates a more gradual feedback time). This is essentially the same thing you’d do with a feedback control on a traditional delay pedal. But with the footswitch functionality, I found myself working with the feedback effect more often, letting the swell roll over big open-position chords like rising surf. It’s a simple effect but the kind of thing that opens up possibilities you might not have considered. And with the modulation effects in the mix, it delivers a lot of extra surprises.  The VerdictThe Warble Swell Echo MkII adds just enough functionality and weirdness to a basic delay-pedal formula to be wild, fun, surprising, and easy to use. Within each control lives a wide range of focused tones and functionality. At its most basic settings, it’s a warmly voiced vintage-style delay. But at its most extreme, the Warble Swell is a fine choice for psychedelic excursions or evoking early studio tape-delay experiments.