Jetstream

Jetstream is Greybound's first flanger model. The reference target is the classic A/DA Flanger family: a wide, musical, BBD-era sweep with manual delay offset, slow liquid modulation, feedback regeneration, and a wet/dry comb path.

The implementation does not copy a factory schematic. It is a graybox model that captures the useful engineering behavior: buffered high input impedance, input/output coupling, BBD-like bandwidth limits, a short fractional delay line, LFO-controlled delay modulation, bounded feedback, wet/dry mix, and low output impedance.

Reference Placement

The reference rig places Jetstream 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 an obvious flange sweep into the amp. It can still be moved to fx_loop in a rig when a post-preamp sweep is desired.

Controls

• manual: base delay offset; lower values sit closer to through-zero-style combing, higher values widen the sweep.
• rate_hz: LFO rate in Hz.
• depth: LFO sweep width around the manual delay.
• feedback: regeneration from delayed output back into the delay input.
• mix: wet/dry blend for the comb path.
• 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 delay path.
• Pre-delay and post-delay low-pass filters approximate BBD bandwidth limits.
• Fractional delay is swept between sub-millisecond and single-digit millisecond delay times.
• Feedback is bounded before re-entering the delay line.
• Wet and dry are recombined to create moving comb notches.
• Output is clamped and exported through a low output source impedance.

Validation

Current validation is behavioral:

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

Useful next checks:

• render swept sine files and inspect moving comb notch frequency,
• compare pre-amp versus FX-loop placement,
• add optional stereo phase offset once the chain has stereo-aware device processors.

References

• The A/DA Flanger is the primary musical reference: wide BBD sweep, manual delay control, and strong regeneration.
• Public BBD flanger schematics are used only as topology references. The source of truth for Greybound remains this model document plus the Rust implementation.