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ASM Hydrasynth Desktop Review



Now that the Hydrasynth is becoming widely available, let’s find out what makes ASM’s flagship synthesizer unique.

In September 2019, a new company called Ashun Sound Machines (ASM) announced that its first synthesizer, the Hydrasynth, was already in production. Never heard of ASM? Perhaps you’re familiar with their VP of Product Development, Glen Darcey. He conceived and brought to market several products for Akai and Arturia.

Deeply complex synthesizers are nothing new. At this price, though, a synth with the sound, usability, features, and build quality of the Hydrasynth certainly is. ASM describes it as a “digital wave-morphing synth with FM and other synthesis methods.” That puts it in a class by itself.

The keyboard model features a ribbon extending the length of its 49 keys that can act as a single-voice pitch controller in Theremin mode. The ribbon can also control pitch bend or modulation alongside the standard wheels to the keyboard’s left. The desktop version is identical in functionality, but without the ribbon or wheels; I bought that one.

Get Acquainted

When I got my Hydrasynth Desktop home, it immediately made a favorable first impression. It has a solid heft and an attractive future-retro design reminiscent of high-end stereos from the 1960s. It even includes a large printed manual and rack ears, though its wall wart hardly inspires confidence.

Powering it up triggers quite a lightshow. Fifty-five buttons and all 24 trigger pads are backlit. When you play them, the pads change color to reflect their function. The two OLED displays are easy to read from any angle, even in bright light. Fifteen LEDs encircle each of the eight rotary encoders to indicate its position.

One reason I chose the Hydrasynth was its support for MIDI Polyphonic Expression (MPE). I dialed up MPE mode and connected it to my Roger Linn Designs LinnStrument. It responded like they were made for each other, just as I’d hoped. My performance gestures produced musical results that felt natural and smooth.

Right away I noticed its presets depend so heavily on effects and deep modulation that they veil their underlying sound. Starting a patch from scratch revealed what I wanted to hear, though: an open, high-definition clarity that I could easily defile into a snarling, beastly roar. I could also make it sound as analog or digital as I wanted.

To hear a rundown of the ASM Hydrasynth’s factory patches, watch this video from Perfect Circuit.

Distinguishing Features

A row of 3.5mm CV jacks appears on the front panel’s top left. Two modulation inputs are intended for control voltages, but they accept audio signals for certain applications. Five are outputs for pitch, gate, modulation (x2), and clock. Pages 7 through 9 in System Setup match the voltages and clocks with external gear. If there’s a voltage range, scale type, trigger type, offset, or clock rate and division that isn’t represented, I’d be surprised.

Below the front-panel jacks are dedicated controls for the arpeggiator, master volume, and filters. In the lower-left corner, the Module Select button array is arranged like a signal-flow diagram from left to right. To edit its settings, press any of the 26 module buttons or, on the upper right, the eight knob-and-button pairs in the Master Control section.

The 24 velocity-sensitive trigger pads are arranged in three rows of eight pads. Remarkably, they respond to polyphonic aftertouch, meaning that each pad responds independently to how hard you press on it. Although they feel good and are useful for programming, I wouldn’t use them as my main controller. You certainly could, though. If you turn off local control and send the pads’ MIDI output to another device, however, you have 24 tunable percussion pads.

Near the unit’s center is the Main Systems display. A large data-entry knob is just above, as well as increment, decrement, and Home buttons below. To its left are buttons that access 11 pages of settings for patch management and system setup. The handy Init button resets a parameter, module, or patch. The Random button lets you randomize a parameter, module, patch, or patch selection, and even the mod (modulation) matrix. The Shift button accesses secondary functions and can modify data-entry speeds.

Around Back

The rear connector panel is inset to allow rackmounting without any need for extra space to accommodate plugs. The main audio, sustain, expression, and headphone outs are 1/4-inch jacks. MIDI In, Out, and Thru are 5-pin DIN connectors. Like most recent synths, the Hydrasynth has a USB type-B client connector for MIDI on the back. I wish it also had a powered type-A host port, which would allow me to connect my LinnStrument directly to the Hydrasynth via USB. As it is, the only way to avoid using a third device is to power the LinnStrument with a USB power supply and use its 5-pin MIDI jack to connect to the Hydrasynth.

Do You Hear Voices?

In the Voice section, you can determine the current patch’s initial structure and feel by adjusting the Hydrasynth’s polyphony, scale, glide, vibrato, and analog simulation parameters.

Each of the eight voices begins with an Oscillator module containing three wavetable oscillators, a noise source, and a ring modulator. All three oscillators can operate in Single mode, wherein you select any of the 219 single-cycle waves in the wavetable and generate sound from a single waveform. Wave selection can be a modulation destination in Single mode, albeit with no crossfading between waves. Oscillators 1 and 2 have a WaveScan mode in which you can list up to eight waves and smoothly crossfade between them, controlled by whatever source you choose in the mod matrix.

Mutants Among Us

Oscillators 1 and 2 also have a pair of Mutant modules that offer eight kinds of waveshaping. FM-Lin (two-operator linear frequency modulation) uses any of the 219 waves, internal sine or triangle waves, the two CV inputs, or another Mutant as either the carrier or modulator. WavStack generates five detuned duplicates of the wave from a single oscillator. It’s much like the SuperSaw waveform on some other synths. OSC Sync is just like hard sync on an analog synth, but with more control over the oscillators’ pitch ratio and synchronization depth.

Whereas PW-Orig is traditional pulse-width modulation, PW-Sqeez and PW-ASM warp the waveform by changing its width on the fly. PW-ASM is particularly interesting because you can design your own custom waveform by specifying values for eight warp points. When you route mod sources to each warp point, you can venture deep into FM territory.

Another type of waveshaping is PhazDiff, which generates sounds ranging from phasing and flanging effects to Karplus-Strong synthesis. Harmonic waveshaping lets you emphasize selected harmonics and attenuate others. In the Ring-Noise Module, you can choose from ten mod sources for the ring modulator’s two inputs. The noise source generates a veritable rainbow of seven colors, including brown, red, blue, violet, and gray.

Filters, Function Generators, and Effects

The ASM Hydrasynth’s digital filters contribute a lot of character to its sound. You can choose between serial or parallel routing. Filter 1 has 11 types to choose from. These include 12 and 24-dB-per-octave slopes, ladder and MS-20 emulation, compensated and uncompensated choices (which determine whether more resonance increases bass response), and lowpass, highpass, and vocal formant types. One standout feature is the variable drive control, which pushes the filters to a warm growl or drives the amp into distortion. Filter 2 is a sweet two-pole state-variable type. Like Oberheim’s SEM filter, it morphs smoothly between lowpass, bandpass, and highpass.

Envelope 1 and LFO 1 are routed to the filters, though you can use them elsewhere via the mod matrix. Envelope 2 and LFO 2 are routed to the Amp module, which has controls to determine overall volume, velocity amount, and LFO 2 modulation amount.

All five DAHDSR (delay-attack-hold-decay-sustain-release) envelopes have variable curves with looping, legato, BPM sync, and free-run modes. All five 11-waveform LFOs have step, sync, delay, fade in, phase, smoothing, and one-shot settings. An LFO’s step mode lets you create patterns with as many as eight steps each, making each of them an analog-style sequencer.

The effects section contains four modules. Pre and Post have one slot each to fill with a pitch-modulation, bit-smashing, EQ, or compression effect. Nestled between them are the delay and reverb. The effects sound very good, and you can use any source in the mod matrix to modulate their parameters.

Mod Matrix, Macros, and Arpeggiator

For each program, the modulation matrix gives you 32 slots to route sources to destinations. With more than 150 sources and hundreds of destinations, it’s hard to imagine you can’t set up any routing you want.

In Macro mode, each knob-and-button pair in the Master Control section lets you manually, simultaneously control as many as eight parameters of any module, as well as CV out, MIDI out, and mod matrix parameters. Because each patch has its own macro setup, you have 16 knobs and switches to shape your sound in real time. You also have with 13 dedicated filter and arpeggiator knobs and switches.

With standard octave, chord, time division, and direction settings, the arpeggiator also features parameters for length, swing, and ratchet with probability control. It supplies 64 stock phrases, too. If you like arpeggiators, you’re going to have fun with this one.

ASM’S Glen Darcey takes you on a tour of the Hydrasynth.


My first synthesizer was a Micromoog. In 1977 I’d stay up all night flipping switches and turning knobs. I was fascinated by their power to shape its beautiful analog tone. I was again sleep deprived in 1991 as I explored the otherworldly and animated sounds of my Wavestation SR, but I was frustrated by its lack of physical controls. With its excellent sound and powerful tools in an inspiring and easy-to-use interface, the Hydrasynth keeps me up nights with the best of both worlds.

The Hydrasynth looks, feels, and sounds fantastic, combining a beautiful analog-like character with wavetable synthesis and deep sound sculpting capability. It approaches a modular system in flexibility and is keenly priced. However, I’d feel better about taking it on the road if it had a more rugged external power supply. At least a standard wall wart should be easy to replace if it fails or gets lost. In future software updates I’d like to see an adjustable MPE bend range to better match other synths, a smooth transition when you change patches, and voice reserve settings. A MIDI host port would be a terrific addition, too, but I know that’s unlikely.

These are minor gripes, really, and ASM continues to work hard at improving the Hydrasynth. Since I bought mine three months ago, they’ve already released two firmware updates. Those gave it powerful new features and two much improved sound banks.

I recommend the ASM Hydrasynth to any synthesist, but especially anyone who loves to build patches from scratch. If that describes you, it offers powerful programming tools and a well-designed, intuitive interface.

For more insight on Ashun Sound Machines, watch Synth Anatomy’s interview from NAMM 2020.


Price: Desktop model, $799; keyboard model $1,299

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