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Sonic Potions/Erica Synths LXR-02

Drum Machine By Rory Dow
Published April 2022

Sonic Potions/Erica Synths LXR-02

Sonic Potions and Erica Synths team up to create a truly unique drum machine.

The Sonic Potions LXR was an affordable DIY project released back in 2014. For those with the requisite soldering skills, it offered a six‑voice FM/subtractive sound engine with a sequencer, four different synth algorithms, MIDI, and open‑source code. Sonic Potions sold the component kit to build the machine and a separate acrylic enclosure. Erica Synths subsequently offered an all‑metal enclosure.

Not everyone has the time or inclination to solder their instruments, so Erica Synths and Sonic Potions have teamed up to create the LXR‑02. It is not available as a DIY kit, and the operating system isn’t open‑source, but otherwise the LXR‑02 doesn’t stray far from the original concept. It’s a six‑voice digital synthesis drum machine with an onboard sequencer. There’s plenty of tweaks and improvements, of course, the addition of volume faders for each voice being the most obvious. Overall the general design philosophy seems to be one of accessible tweakability. Rarely is anything more than a click or two away, and you can edit everything without stopping the sequencer.

Synthesis

The LXR‑02 uses a combination of subtractive and FM synthesis. There are four main algorithms: Drum, Snare, Cymbal/Clap and Hihats. The synthesis parameter pages are cleverly grouped so that no matter which type of sound you are editing, you can hit a button and go to the relevant page for that algorithm. No matter whether you’re editing a snare or a hi‑hat, if you hit the Filter button, you always go to the filter page for that algorithm.

The first three channels use the Drum algorithm, a mix of simple FM and subtractive synthesis. The primary use is probably kicks and basses, but they can easily make toms, percussion, snares, laser zaps, etc. The Snare channel is more focused and uses subtractive oscillators and noise to create snares and percussive hits. The Cymbal and Hihats channels use a more complex FM setup to create metallic, enharmonic sounds. The Open and Closed Hihat channels use the same synthesis parameters except that each can set a different amplitude decay time. They can then be sequenced separately but will choke each other.

Mostly, the synthesis modules used in each drum algorithm are similar. The oscillators create classic analogue waveforms: sine, triangle, sawtooth, rectangle (aka square), noise and PWM. The filters are a 2‑pole state‑variable design with low‑pass, high‑pass, band‑pass, unity gain band‑pass, notch, and peak filter types.

The envelopes are a simple AD design but offer variable exponential and logarithmic curve controls and a repeat parameter that causes rapid retriggering — useful for synthesizing clap sounds. The Drum and Snare algorithms offer two envelopes, one for amplitude and one for pitch modulation. The pitch envelope can also automate a long list of destinations with optional velocity sensitivity. The Cymbal algorithms offer only one amplitude envelope but still provide velocity modulation over many possible destinations.

All algorithms offer a Click page where you can alter the transient using either an additional short pitch envelope, adjusting the starting phase of the main oscillator or mixing in a transient sample. The samples are baked into the firmware and cannot be replaced but offer variants such as acoustic kick, rim‑shot, hi‑hat, clap, tom and finger snap. The samples are short but valuable for adding a consistent transient to any sound.

Each voice has an LFO, which can free‑run or sync to an internal or external clock. It can only control one parameter, but that can be any parameter (including effects) on any voice. Effectively then, you have six freely assignable, global LFOs. Possibly my favourite detail is that you can assign any voice to reset the phase of the LFO. It means you could have a kick drum retriggering the LFO on a percussion track which is controlling some wild modulation. This interaction between sequencer tracks makes for some exciting and dynamic patterns.

A big part of the LXR‑02 sound is overdrive. Both the filter and the output can be overdriven for each drum voice, resulting in sounds ranging from clean and polite to downright filthy. If that still sounds too pleasant, you can add some bit‑depth reduction, which will cause anything from a touch of aliasing to total annihilation. Bit‑depth reduction is also available on the master mix outputs. In all, there is a ridiculous number of ways to roughen up the sound.

If you make any genre of music that benefits from synthesized drum sounds —...

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