Review: Beepstreet Zeeon

This stand-out iOS synth could be your new best sonic friend
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After a decade of iOS synthesizers, it’s no exaggeration to say that standard dual-oscillator subtractive synths are plentiful. So, with countless existing choices for this type of synthesis, it’s amazing that BeepStreet has managed a way to step away from the crowd with their newest synth, Zeeon.

Zeeon’s timeless analog architecture will be familiar to many, and its filter ofers models of three classic analog circuits

Zeeon’s timeless analog architecture will be familiar to many, and its filter ofers models of three classic analog circuits

At first glance, Zeeon isn’t particularly remarkable, with two oscillators, a sub oscillator, noise generator, and filter, along with two ADSRs and two LFOs on modulation duties: We’ve seen that before. What separates Zeeon from the pack is its array of customization tools for getting tantalizingly close to the behavior of true analog synthesizers.

For the oscillator pair, there’s a Vintage button that gives their sound a bit more retro flavor, but diving into the Panel 2 section opens up a second set of parameters for tailoring this even further. The Slop knob adds a touch of randomized pitch drift, while the PSU imparts the jitter of a decaying power supply.

The filter offers three modes, 4-pole transistor ladder (Moog), 4-pole OTA (Roland/Korg), and 2-pole state-variable (Oberheim). All are credible replicas that capture many of their respective frequency response characteristics, with the OTA being rather smooth. Here, there are tone controls for the first two models and a State knob for the third that sweeps from lowpass to notch to high-pass, and then band-pass.

There’s also a switch for Bias that’s extremely subtle until the resonance is set to 50% or higher, at which point it adds a bit of dirtiness to the resonant peak. The Drive section also includes both pre- and post-filter routings, along with three additional distortion modifiers.

While the LFOs and ADSR envelopes appear traditional in their implementation, a Saturation parameter on Panel 2 pushes the envelope curves into logarithmic/exponential territory. That said, Zeeon’s 8-way modulation matrix is capable of some extraordinary tricks. Here you’ll find impressive audio-rate modulation options from the oscillators, the sub-oscillator, and three different noise types — all available as sources. Applying these to destinations such as pitch, waveform/pulse-width, or filter cutoff provides results ranging from grit and grime to full-on chaos, or better still, you can route these audio-rate sources to the modulation depth of other destinations.

Both layers feature the same synthesis amenities, but are processed by a set of four effects — chorus, phaser, delay, and reverb. While the phaser, delay, and reverb are certainly digital, the chorus is another analog-flavored standout, offering triangle or sine modulation, and circuit noise. Additionally, the delay section incorporates both drift and either low- or high-pass filtering in the feedback loop, which adds to its decidedly old-school vibe.

Dedicated iOS producers will already have a collection of synths that overlap with these features, but to date, none have the detail and behavior adjustments that Zeeon delivers. What’s more, the audio-rate modulation can generate some astonishingly chaotic effects. Extended polyphony and complex layered patches will impact CPU overhead, but if you’ve got an iPad and 10 bucks to spare, this is a great synth.

Effectively recreates many idiosyncrasies of vintage analog circuits. Two synth layers with inter-layer modulation options. Audio-rate modulation from oscillators. 4x oversampling.

CPU-heavy on older iPads


Francis Preve has been working with analog synths for over 30 years. Get the full story at