Celeste

Celeste is Greybound's first chorus model. The reference target is the classic Boss CE-2 family: musical analog chorus with a short BBD delay, slow LFO motion, rounded bandwidth, and a smooth wet/dry blend.

The implementation does not copy a factory schematic. It is a graybox model that captures the useful engineering behavior: buffered high input impedance, input coupling, BBD-like bandwidth limits, two gently detuned modulated delay voices, wet-path tone shaping, wet/dry mix, and low output impedance.

Reference Placement

The reference rig places Celeste before the amp input:

• guitar/source loading through ConnectionState,
• nominal high input impedance,
• modulated delay before Nox30 preamp drive,
• low output source impedance into the next chain slot.

This placement gives the familiar pedal-into-amp chorus feel. Celeste can also be moved into fx_loop when the rig should chorus the amp preamp output instead.

Controls

• rate_hz: LFO rate in Hz.
• depth: LFO sweep width.
• tone: wet-path brightness.
• mix: wet/dry blend.
• bypass: routing state; private LFO and delay state remain owned by the pedal instance.

DSP Mapping

• Input boundary uses ConnectionState with high input impedance and cable capacitance.
• Input coupling removes DC before the BBD-style path.
• Pre-delay low-pass filtering limits the signal entering the delay lines.
• Two fractional delay lines use different LFO offsets to create a wider mono chorus.
• Wet-path low-pass filtering supplies the darker analog voice.
• tone blends the darker wet voice with the brighter raw delayed voice.
• Output is clamped and exported through a low output source impedance.

Validation

Current validation is behavioral:

• deeper sweep changes output versus a shallow sweep,
• active chain output remains audible,
• rig parser accepts all Celeste controls,
• CLI runtime controls are shared atomics so the monitor can edit controls without locking the audio callback.

Useful next checks:

• render swept sine and chord samples to inspect pitch-motion smoothness,
• compare pre-amp versus FX-loop placement,
• add stereo left/right delay offsets when the chain has stereo-aware device processors.

References

• The Boss CE-2 family is the primary musical reference: compact analog BBD chorus with rate/depth-style modulation and a smooth, rounded wet path.
• Public BBD chorus schematics are used only as topology references. The source of truth for Greybound remains this model document plus the Rust implementation.