openDIAW.be/plans/base-frequency.md

Configurable Base Frequency (Concert Pitch)

Context

midiToHz in @opendaw/lib-dsp converts MIDI note numbers to Hz using a base frequency (default 440 Hz). Some musicians prefer alternative tunings like A=432 Hz. The base frequency is stored per-project in RootBox and exposed as a convenience getter on EngineContext so processors don't need to navigate the box hierarchy.

Call Site Analysis

Call site	File	Thread	Has EngineContext?	Impact
VaporisateurDeviceProcessor.computeFrequency	core-processors/.../VaporisateurDeviceProcessor.ts:153	AudioWorklet	Yes — this.context	Must use this.context.baseFrequency
SoundfontVoice.processAdd	core-processors/.../SoundfontVoice.ts:79	AudioWorklet	No — plain class	No change — base frequency cancels out in pitch ratio
ScriptRunner / Api.ts	scripting/src/ScriptRunner.ts:27, Api.ts:17	Web Worker	No — only sampleRate in context	Inject setting into script context
nano-wavetable.ts example	app/studio/.../nano-wavetable.ts:21	Web Worker	No — example script	No change
ParameterDecoder.readValue	lib/dawproject/src/utils.ts:29	Main thread	No — static utility	No change — DAWproject uses standard 440 Hz per spec
semitoneToHz / hzToSemitone	lib/dsp/src/utils.ts:18-19	Various	N/A	Add baseFrequency parameter (default 440) like midiToHz already has

Overview of Changes

1. Add baseFrequency field to RootBox

packages/studio/boxes/src/RootBox.ts

Add a Float32Field at field key 50 with range 400–480 Hz, default 440, linear scaling.

2. Add baseFrequency getter to EngineContext

packages/studio/core-processors/src/EngineContext.ts

get baseFrequency(): number

3. Implement getter in EngineProcessor

packages/studio/core-processors/src/EngineProcessor.ts

get baseFrequency(): number {return this.#rootBoxAdapter.box.baseFrequency.getValue()}

4. Add baseFrequency parameter to semitoneToHz and hzToSemitone

packages/lib/dsp/src/utils.ts

Add default parameter matching the pattern midiToHz already uses. Existing callers unchanged.

5. VaporisateurDeviceProcessor — read from context

packages/studio/core-processors/src/devices/instruments/VaporisateurDeviceProcessor.ts

computeFrequency(event: NoteEvent): number {
    return midiToHz(event.pitch + event.cent / 100.0, this.context.baseFrequency)
}

6. Scripting API — expose base frequency

• ScriptExecutionContext — add baseFrequency: number field
• CodeEditorPage.tsx — read from project.rootBox.baseFrequency.getValue()

7. UI for base frequency setting

TBD — expose the RootBox.baseFrequency field in the project settings UI.

Key Files Modified

File	Change
packages/studio/boxes/src/RootBox.ts	Add baseFrequency Float32Field (key 50, default 440, range 400–480)
packages/studio/core-processors/src/EngineContext.ts	Add get baseFrequency(): number to interface
packages/studio/core-processors/src/EngineProcessor.ts	Implement getter reading from rootBoxAdapter.box.baseFrequency
packages/lib/dsp/src/utils.ts	Add baseFrequency param to semitoneToHz / hzToSemitone
packages/studio/core-processors/src/devices/instruments/VaporisateurDeviceProcessor.ts	Use this.context.baseFrequency
packages/studio/scripting/src/ScriptExecutionProtocol.ts	Add baseFrequency to ScriptExecutionContext
packages/studio/scripting/src/ScriptRunner.ts	Inject baseFrequency into script globalThis (via ...context spread)
packages/app/studio/src/ui/pages/CodeEditorPage.tsx	Pass baseFrequency from project root box

Notes

• The value is stored in the project via RootBox and persists with save/load.
• this.context.baseFrequency reads directly from the box field, so changes are reflected immediately.
• Future instrument processors should follow the same pattern: read this.context.baseFrequency instead of hardcoding 440.