Springfield

Springfield is Greybound's first reverb model. It targets the musical behavior of a guitar spring reverb: a driven transducer feel, short metallic diffusion, bright splash, and a controllable wet/dry blend.

The first implementation is a stable graybox model, not a component-exact spring tank simulation. It is intended to be useful in the rig now while leaving room for a later tank/transducer model.

Baseline Assumptions

• Buffered input with about 1 MOhm input impedance.
• Low output impedance suitable for driving an amp FX return or another post-preamp device.
• Best default placement is fx_loop, after preamp drive and before the power section.
• The wet path has private delay/tank state.
• Bypass is routing state; the active tank state remains private to the Springfield instance.

Controls

• dwell: drive into the spring tank and feedback intensity.
• tone: tank brightness and splash emphasis.
• mix: wet/dry blend.
• bypass: routing state.

External Boundaries

The effect receives and emits voltage plus impedance:

• input source: amp FX send, previous FX-loop device, guitar pickup, or previous pedal output,
• input load: Springfield input impedance plus cable capacitance memory,
• output source: reverb-mixed voltage plus output impedance,
• output load: amp FX return, next pedal, or post-amp section.

ConnectionState owns cable capacitance and source/load division. Springfield should not mutate amp internals.

Current DSP Approximation

The current implementation uses:

• source/load input boundary and input coupling,
• dwell-dependent input drive into the tank,
• four short delay lines with cross-fed feedback to mimic spring dispersion,
• tone-dependent pre-emphasis and wet-path brightness,
• output low-pass smoothing,
• wet/dry mix with conservative level scaling,
• low output source impedance.

Validation Gates

The model is not component-exact until:

• dwell sweep is checked for stable decay and useful drive range,
• tone sweep changes splash/brightness without runaway level,
• mix sweep preserves dry level at low settings and gives a musical wet blend at high settings,
• bypass behavior preserves the direct path,
• FX-loop placement and post-amp placement produce expected musical differences,
• measured or SPICE captures define a specific spring tank reference.