Walnut SignalA small synthesizer becomes a playable pocket instrument.

Walnut Signal is a native iPhone instrument built to teach subtractive synthesis by ear: make a sixteen-step phrase, shape one oscillator through one resonant filter, and follow four deliberate modulation routes without confronting a wall of modules.

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The operating reality

The first working build proved the clock, sequencer, and audio seam, but it still read as engineering scaffolding. The real product challenge was to make signal flow understandable through musical gesture while preserving the precision and tactility of a premium instrument.

What exists now

The release-candidate surface now joins a module-first Instrument Home, sixteen-step Pattern Composer, guided Signal Path Studio, keyboard audition, and a local patch library in one coherent native product. Walnut rails, smoked metal, brass controls, and restrained signal light give the instrument its own physical identity.

Selected evidence

A signal path you can learn by playing.

Release-candidate screens show the actual native interaction; physical listening and store release remain human gates.

Walnut Signal instrument workbench with oscillator, filter, envelope, and movement modules.

Instrument home

The signal path is playable before it is explained.

Oscillator, low-pass filter, envelope and VCA, and movement controls live in one module-first workbench. The physical visual language makes each section distinct without disguising what the controls actually do.

Walnut Signal Pattern Composer with sixteen direct steps and selected-step controls.

Pattern performance

Sixteen steps stay direct, musical, and editable.

The composer keeps the full pattern, selected-step controls, phrase choices, and key transpose close enough to change while the loop is moving, with updates joining cleanly at the sequence boundary.

Working artifacts

The instrument beneath the visual identity.

Audio behavior, sequence timing, local storage, accessibility, and release evidence are treated as one product.

Module-first instrument

One oscillator, one resonant low-pass filter, a full ADSR and VCA, and deliberate movement controls form a learnable subtractive voice.

Pattern and signal studios

A sixteen-step performance composer and four-route signal view let the player move from musical results into exact patch relationships.

Local-first release candidate

Saved patches remain on-device, the public policy states the privacy boundary, and deterministic Simulator evidence remains separate from physical listening and release approval.

Public proof

The iPhone 17e / iOS 26.5 Simulator suite passes 74 of 74 tests. Fresh unsigned Debug and Release Simulator products build, and the release-candidate captures cover standard and accessibility-large composition. Earlier private builds were signed, installed, and launched on an iPhone through the local development lane.

Boundary

Walnut Signal is not yet on the App Store. Long-play physical listening, touch feel, full VoiceOver traversal, production signing and archive validation, store metadata, and submission remain explicit human gates. It is a bounded native instrument, not a third-party modular-platform clone or compatibility claim.

Relevant next step

Build the smallest instrument worth learning.

Start with the musical gesture and the exact product boundary, then carry both through native implementation and release QA.

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