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Audio tools for iPhone, iPad, Mac & Android — and for your family!

RSJB is an independent Brazilian studio that builds apps focused on music and family — no ads, no tracking!

Our apps

Three tools, one philosophy.

Tonic Synth

On the App Store

Three layers, eight sound engines per layer, eight analog filters and a full effects rack — in your pocket, standalone or inside your DAW.

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Tonic FX

On the App Store

34 effects you build, reorder and play live: drive, modulation, voice, delay, reverb, EQ and dynamics.

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Tonic Filter

Coming soon

Tonic's filter section in one effect app: eight analog characters and an envelope that listens.

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Rsf2

In stores

Merge, split and reorder presets — byte-exact and on-device.

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RDX

On the App Store

Open, preview and build .syx banks from classic FM synths.

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REXS

On the App Store

Organize, play and convert your .exs instruments to SoundFont — without Logic.

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In the press

AudiofanzineFrench music & audio platform

A news post on Tonic 2 — a three-layer synth for iPhone, iPad and Mac: 3D wavetables, a Vector XY pad, a 12-mode arpeggiator and eight sound models per layer, standalone and AU/AUv3.

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AMAZONA.deGerman synth magazine

A feature on Tonic — an analog-modeling synth with eight synthesis engines, three layers, analog filters and AUv3.

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Focused tools, no distractions

Audio apps to create, organize and play your music — no ads, no tracking. Crafted with care, in Brazil.