ROM-Rot v2.5 — Hybrid Chiptune Synth & Tape Lo-Fi Processor

ROM-Rot v2.5 is a cross-platform (VST3/AU) hybrid plug-in synthesizer and audio degradation effects processor. It seamlessly combines 8-bit wavetable synthesis (Chiptune) with analog hardware emulation (Tape Lo-Fi) and advanced digital downsampling algorithms.

The plug-in architecture is divided into 5 independent control windows (tabs) featuring a continuous stereo audio stream, a global ROT macro controller, and an integrated real-time oscilloscope. A standout feature is the Retro ROM Exporter terminal, which translates the current sound parameters into functional source code for retro hardware and virtual consoles (PICO-8, NES, SEGA, GameBoy).

---

🚀 Key Features

• Dual Target Architecture (Synth & FX): Operates either as a fully polyphonic instrument with MIDI input or as a standalone insert effect for processing external audio.
• Hybrid DSP Engine: Authentic discrete approximation of retro hardware waveforms combined with physical modeling of magnetic tape degradation.
• Intelligent Chord Assistant: Automatic scale quantization (Scale Lock) and retro arpeggio generation mimicking classic hardware limitations.
• Low-Level Code Export: Instantly translate your sound patches into compilation-ready C, Lua, or 6502/Z80 assembly code.
• Lock-Free Architecture: Thread-safe real-time audio processing completely isolated from the UI thread without using mutexes.

---

🛠 Technical Architecture & DSP Specifications

1. Thread Safety & Dual Target Routing

Developed in C++20 utilizing the JUCE 7.0.12 framework[cite: 1]. The build system is managed via CMake, configuring two distinct plugin targets that share a core codebase[cite: 1]:

• LofiChiptuneSynth (with IS_SYNTH TRUE) — A polyphonic synthesizer instrument[cite: 1].
• LofiChiptuneSynthFX (with IS_SYNTH FALSE) — A stereo audio effects processor[cite: 1].

To ensure strict real-time safety, communication between the UI thread and the Audio Thread is completely lock-free[cite: 1]:

• Automation parameters are bound to juce::AudioProcessorValueTreeState (APVTS)[cite: 1].
• Inside processBlock(), parameter pointers are cached as std::atomic<float>* and read using relaxed memory ordering (std::memory_order_relaxed)[cite: 1].
• UI tab switching is handled by a custom WindowStateManager using atomic variables with release / acquire ordering synchronization[cite: 1].

2. Synthesis Engine (OSC Tab)

Handled via SynthVoice and LofiChiptuneSynthAudioProcessor classes[cite: 1].

• Polyphony: Supports up to 8 independent voices allocated cyclically[cite: 1]. Features a custom voice stealing algorithm that smoothly fades out the oldest active voice to completely eliminate audio clicks[cite: 1].
• Oscillator Waveforms:
  • Sine: A mathematically pure sine wave with zero harmonic distortion, ideal for warm low-end control and sub-basses.
  • Triangle: An authentic 16-step discrete approximation of a triangle wave[cite: 1]. Instead of a smoothed linear ramp, the algorithm quantizes the waveform amplitude into 16 fixed levels[cite: 1]. This perfectly emulates the hardware constraints and the distinct "woody", clicking character of the Ricoh 2A03 sound chip (NES/Dendy)[cite: 1].
  • Sawtooth: A linear sawtooth wave containing a full spectrum of even and odd harmonics for aggressive cyber-chiptune, Witch House, and Synthwave leads.
  • Pulse (PWM): A rectangular wave with dynamic Pulse Width Modulation, extended by manual PULSE WIDTH offset (50% down to 12.5%) and a dedicated internal PWM LFO (pwm_rate and pwm_depth)[cite: 1].
• Synthesis Utility Controls:
  • DETUNE: Micro-pitch detuning between oscillator phases for wide analog unison and stereo widening[cite: 1].
  • SUB OSC: Mixes a pure sine wave exactly one octave below the fundamental frequency for massive low-frequency foundations[cite: 1].
  • NOISE OSC: Controls the gain of a pseudo-random white noise generator, essential for adding Lo-Fi texture, dust, or chiptune percussion bursts[cite: 1].
• Amplitude ADSR Envelope: Vertical faders controlling a non-linear juce::ADSR envelope to shape volume dynamics from instant retro clicks to smooth pads[cite: 1].

3. Audio Degradation Module (FX Tab / "ROT" DSP Engine)

Implemented in the LofiEngine class, processing audio through sequential non-linear and time-based degradation algorithms[cite: 1]:

• Wow & Flutter (Tape Speed Instability): Utilizes a stereo circular delay buffer (delayBuffer[2]) of 4096 samples (~90ms delay)[cite: 1]. Wow models low-frequency speed variations via an LFO (~1.0–2.2 Hz)[cite: 1]. Flutter simulates high-frequency tape jitter (~8.0–14.0 Hz) modulated by random micro-noise to prevent artificial periodicity[cite: 1]. To eliminate digital artifacts during continuous delay time modulation, linear fractional interpolation is applied[cite: 1]: $$output = sample[floor] \cdot (1 - frac) + sample[floor + 1] \cdot frac$$
• "Melt" Effect: A random algorithm generating sudden, deep playback speed drops (delay sharply spikes up to 35 samples), replicating physical tape damage[cite: 1].
• High-Shelf Filter (HF Roll-off): A 1st-order one-pole smoothing low-pass filter emulating magnetic tape head high-frequency loss[cite: 1]: $$output[n] = state + \alpha \cdot (input[n] - state)$$ The $\alpha$ coefficient dynamically scales from 1.0 (clean bypass) down to 0.3 (deep HF cut) based on the global macro control[cite: 1].
• Tape Saturation: Non-linear harmonic distortion driven by a hyperbolic tangent function with automatic gain compensation[cite: 1]: $$saturated = \tanh(input \cdot saturationDrive)$$
• Bitcrusher (Digital Destruction):
  1. Sample & Hold (Downsampling): Subsamples the stream, holding values based on the 1.0 / sampleRateRatio[cite: 1].
  2. Amplitude Quantization (Bit Reduction): Rounds the sample to the nearest allowed discrete level based on the selected bit depth (down to 4-bit)[cite: 1]: $$crushed = \frac{\text{round}(input \cdot levels)}{levels}$$
• Vinyl Crackle: A random generator creating impulses with a defined probability (crackleLevel * 0.00008f), shaped through a 1st-order IIR bandpass filter to sound like soft, organic dust crackles[cite: 1].
• Horror Reverb: Built on juce::Reverb[cite: 1]. As the global macro slider increases, it dynamically scales the room size (roomSize up to 0.92) and wet level (wetLevel up to 0.45) for an immersive eerie space[cite: 1].

---

🎹 Pattern Automation & Chord Routing

Handled within SynthVoice when parsing incoming MIDI data streams[cite: 1].

• Scale Lock: A specialized array filtering semitones (scaleSteps)[cite: 1]. If a played note falls outside the chosen musical scale (Major, Minor, Pentatonic, Dorian, Phrygian, Lydian, Mixolydian), it instantly snaps down to the nearest allowed step within the selected root key (keySelect)[cite: 1].
• Chord Assistant: Automatically translates single MIDI notes into complex triads or 7th chords[cite: 1].
• Retro Arpeggio Mode: Breaks down chords into a rapid cyclical arpeggiation cycle (35 Hz)[cite: 1]. This perfectly recreates the authentic style of NES/GameBoy sound chips that lacked hardware polyphony[cite: 1].
• DAW MIDI Export: Fully supports native OS Drag-and-Drop. Allows musicians to drag the generated arpeggio or chord pattern directly out of the plugin window as a .mid file into any modern DAW timeline or Piano Roll (FL Studio, Ableton Live, Reaper, Cubase, etc.).

---

👾 Low-Level Code Terminal: Retro ROM Exporter

The RetroRomExporter.h and RomExportWindow.cpp modules analyze the current audio engine properties and translate them into production-ready assembly or high-level source code for retro architectures[cite: 1]:

1. PICO-8 SFX (Lua): Outputs Lua arrays containing pitch, volume, effects, and waveform data mapped to PICO-8's sound subsystem memory via poke() function calls[cite: 1].
2. NES 2A03 (6502 ASM): Generates 6502 assembly byte tables initializing the NES APU, writing volume, duty cycle, and period values straight to hardware registers $4000 / $4002[cite: 1].
3. SEGA Genesis (YM2612 Regs): Compiles C-arrays or assembly code mapping FM operator registers for the YM2612 chip (including feedback, algorithm routing, frequency multipliers, and hardware ADSR parameters)[cite: 1].
4. GameBoy Color (GBDK C-Code): Outputs clean C source code for the GBDK compiler, writing directly to the GameBoy hardware sound registers (NR10 to NR14) to control the primary pulse channel[cite: 1].

---

🎨 UI/UX and Visualization

The user interface features a sleek, unified Dark Neon Synthwave aesthetic.

• Typography: Text components are rendered using the modern geometric typeface Outfit, embedded natively into the plugin's binary resources[cite: 1].
• CustomLookAndFeel: A complete override of JUCE's default rendering engine[cite: 1]. Sliders are drawn as custom glowing neon gradient rings with a distinct center indicator.
• Tape Animation: The FX tab runs an internal 30 Hz timer thread animating two rotating cassette spools[cite: 1]. The rotational speed is dynamically modulated by the active audio thread's Wow & Flutter parameters to visualize tape drag in real time[cite: 1].
• Stereo Oscilloscope: The OscilloscopeComponent processes data out of a 2048-sample lock-free ring buffer[cite: 1]. It draws a neon-pink representation of the waveform in real time, visually demonstrating bitcrusher quantization steps without causing audio processing overhead[cite: 1].

---

📦 Build Instructions

Dependencies

• C++20 compatible compiler (MSVC 2022 / GCC 11+ / Clang 13+)
• CMake 3.22 or higher
• JUCE 7.0.12 (managed automatically via CMake FetchContent or as a git submodule)

Building via Terminal:

git clone https://github.com/AlexeyNazariev/ROM-Rot.git
cd ROM-Rot
cmake -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build --config Release

Compiles artifacts (.vst3, .component) into the build/ROM-Rot_artefacts/ directory.

---

📄 License

This project is licensed under the terms of the MIT License. You are free to use, modify, and distribute this codebase for both non-commercial and commercial projects. See the LICENSE file for details.

Developed by: Alexey Nazariev