Echoform

Echoform is a JUCE-based stereo memory-delay AU/VST3 plug-in inspired by the Chase Bliss Habit. It features dual playheads, automatic scanning, deterministic randomness, and a modifier chain that can be configured into different feedback and stereo behaviors.

Features

• Dual playheads with manual scan and automatic wander
• Deterministic random modulation (seeded by randomSeed + host transport position)
• Modifier chain: wow/flutter, dropout, low-pass, pitch drift
• Feedback modes: Collect, Feed, Closed
• Routing modes: In, Out, Feed (per bank)
• 3-minute memory buffer with size-scaled scan/spread
• Stereo modes: Independent, Linked, Cross
• Token-based LookAndFeel loaded from resources/visualdna_tokens.json
• Inspect mode with a non-literal memory timeline and playhead positions

Parameters

• mix: Dry/wet mix (0 = dry, 1 = wet)
• scan: Manual scan depth (0 = now, 1 = max delay)
• scanMode: Manual / Auto
• autoScanRate: Automatic scan rate in Hz (0 = manual only)
• spread: Normalized offset between playheads (scaled by size)
• feedback: Feedback amount (clamped for stability)
• size: Maximum delay length in seconds (0.05 - 60)
• bankA_mod1..3: Bank A modifiers (mod1 wow/flutter, mod2 dropout, mod3 tone)
• bankB_mod1..3: Bank B modifiers (mod1 wow/flutter, mod2 dropout, mod3 tone)
• character: Macro controlling modifier intensity
• stereoMode: Independent / Linked / Cross
• mode: Collect / Feed / Closed (Feed recirculates the processed effect; Closed loops full output)
• routingA: In / Out / Feed (controls where Bank A applies)
• routingB: In / Out / Feed (controls where Bank B applies)
• always: Record while bypassed
• wipe: Audition memory directly (wet only)
• dryKill: Disable the dry path
• latch: Freeze playback/write (hidden)
• trails: Allow wet tails while bypassed (hidden)
• memoryDry: Force dry-only while bypassed even if trails (hidden)
• randomSeed: Seed for deterministic randomness

Build

1. Install JUCE and update JUCE_DIR in CMakeLists.txt.
2. Configure the build:

cmake -S . -B build

3. Build the plug-in:

cmake --build build

Design Tokens

The UI reads tokens from resources/visualdna_tokens.json. If the file is missing or incomplete, the plug-in falls back to built-in defaults.

QA Test Harness

Echoform includes comprehensive QA scenarios using the audio-dsp-qa-harness:

• 42 scenarios covering feedback modes, stereo modes, modulation, routing, spatial acoustics, stress tests, and contract checks
• Latest local run: 41 passing, 1 warning, 0 failures
• Native stimulus types including room simulation for spatial testing
• Contract pack adoption: latency, parameter smoothing, and state integrity contracts are included in critical/comprehensive suites

Test Categories

1. Core Functionality: Smoke test, determinism, buffer wraparound
2. Feedback Modes: Collect, Feed, Closed (3 scenarios)
3. Stereo Modes: Independent, Linked, Cross (3 scenarios + 1 spatial)
4. Modulation: Wow/flutter, dropout, tone (3 scenarios + 1 spatial)
5. Routing: Bank A/B input/output/feed combinations (5 scenarios)
6. Parameter Sweeps: Mix, scan, feedback, character (4 scenarios)
7. Spatial Acoustics: Feedback decay, tape mode ambience, cross stereo (3 scenarios)
8. Stress Tests: Determinism, buffer extremes, feedback saturation (3 scenarios)

Running Tests

# Run critical suite (8 scenarios)
./build_qa/echoform_qa_artefacts/Release/echoform_qa scenarios/echoform_critical_suite.json

# Run comprehensive suite (42 scenarios)
./build_qa/echoform_qa_artefacts/Release/echoform_qa scenarios/echoform_comprehensive_suite.json

# Run individual scenario
./build_qa/echoform_qa_artefacts/Release/echoform_qa scenarios/echoform/smoke_test.json

# Run with performance profiling
./build_qa/echoform_qa_artefacts/Release/echoform_qa scenarios/echoform_performance_suite.json --enable-profiling

State integrity currently uses a proxy contract because the embedded harness snapshot in this repo does not yet expose the newer native state roundtrip APIs. This scenario should be migrated to true state_roundtrip once the harness snapshot is updated.

See docs/SPATIAL_SCENARIOS_RETROACTIVE_IMPROVEMENTS.md for details on the 3 new spatial scenarios that test echoform with room acoustics.

Legacy Determinism Test

src/DeterminismTest.cpp registers a JUCE UnitTest that processes identical input twice with the same seed and asserts bit-identical results. Run it from a JUCE unit test runner if you wire one into your host or standalone app.