Scopion Manual — Precision Stereo Oscilloscope & FFT Spectrum Analyzer

📖 Table of Contents (Tap to Navigate)▼

1. Visual Overview

Scopion (v1.0.0, by vanBuffelen) is a completely free, zero-latency studio Stereo Time-Domain Oscilloscope (SIGNAL) and Calibrated Hann FFT Spectrum Analyzer (SPECTRUM) built in Rust (nih-plug + nih_plug_egui). Designed in the Nordic Daylight Minimal aesthetic (1040 × 640 baseline, proportionally scalable up to 3840 × 2160), Scopion pairs laboratory measurement precision with crisp, glare-free visual ergonomics.

Scopion Time-Domain Oscilloscope in Blueprint Theme

Figure 1.1: SIGNAL Mode — Time-domain stereo waveform in the Blueprint scope palette with cursor amplitude/dBFS readout.

Scopion Spectrum Analyzer Frozen State with Dual-Channel and REF Traces

Figure 1.2: SPECTRUM Mode — Frozen 2048-point calibrated FFT with live CH L, CH R, and dashed REF A/B curves.

Scopion Spectrum Analyzer Deep Zoom on Sub-Octave Logarithmic Grid

Figure 1.3: Deep-Zoom Harmonic Inspection — Adaptive sub-octave logarithmic grid at 8192-point FFT resolution.

2. Key Strengths & Engineering Highlights

1. Sub-Sample `30 Hz ZEROS` Trigger

An RBJ 2nd-order Butterworth lowpass filter (fc = 30 Hz, Q = 1/√2) isolates the fundamental period despite distortion, harmonics, or DC offset, while linear zero-crossing interpolation (< 0.5% spread at 1 ms zoom) eliminates 1-sample horizontal jitter.

2. Three-Stage Adaptive Waveform

Renders Catmull-Rom cubic splines below 1 sample/px, 100% raw exact samples from 1..12 samples/px (up to ~225 ms at 48 kHz), and chronological [min, max] sub-pixel envelopes across the full 1.5 s history buffer.

3. Laboratory-Calibrated `f64` FFT

Single-pass complex stereo Radix-2 Cooley-Tukey FFT (256–32,768 points, zero heap allocations) using a mean-normalized Hann window (2/N AC, 1/N DC) so a 0 dBFS sine wave reads exactly 0.00 dB.

4. Instant `REF` A/B Memory Trace

Capture a full-resolution snapshot of both stereo time-domain and FFT curves with one click on REF, rendered as a uniform arc-length dashed overlay that re-projects dynamically as you zoom, pan, or switch modes.

Asymmetric Ballistic Smoothing + Peak Envelopes: Fast attack (0.65) and smooth release (0.22) eliminate inter-frame phase-scalloping jitter while preserving sharp harmonic peaks across multi-bin high-frequency columns.
Zero-Latency Audio Pass-Through: In DAW hosts (CLAP, VST3, Apple AUv2), Scopion adds 0 samples of latency and touches zero audio samples on the output path.

3. Interface Tour & Resizable Window

Row 1 — Studio Header Bar

Control	Function
Scopion Emblem	Procedural 4× Retina (`304 × 192`) geometric scorpion + oscilloscope pulse emblem (`vanBuffelen · v1.0`).
Window Size (%)	Header percentage preset dropdown (`75%`, `85%`, `100%`, `115%`, `125%`, `150%`, `175%`, `200%`) — scroll wheel to step, or double-click to reset to `100%` (`1040 × 640`).
Stereo Input Monitor	Displays active host/hardware Sample Rate (`44.1 kHz – 192 kHz`), dual L / R peak-and-hold meters, numerical peak readout in dBFS, and clickable Clip LED (clears peak hold).
SIGNAL / SPECTRUM	Primary segmented switch between the Time-Domain Oscilloscope and Fourier Spectrum Analyzer.
FREEZE / \|\| FROZEN	Latches the `262,144`-sample (`~5.4 s` at `48 kHz`) lock-free ring buffer and lights up the top-right `\|\| FROZEN` stage badge.
Export	Opens the Export Plot (`PNG` / `SVG`) modal dialog up to `7680 × 4320` (`8K`).

Row 2 — Contextual Analyzer Stage Bar

Mode-Dependent Left Controls

In SIGNAL Mode: Switch between FREE RUN (rolling 0–55 ms default, zoomable to 1.50 s) and 30 Hz ZEROS (sub-sample Butterworth rising zero-crossing lock).

In SPECTRUM Mode: Choose FFT Length (256 to 32768, default 8192) and toggle LOG (15.625 Hz – 32 kHz) vs. LIN (0 Hz – Nyquist).

Always-Available Right Controls

Toggle CH L / CH R traces, click REF to capture or toggle the dashed A/B memory trace (right-click to re-capture), hit Reset to restore factory axis bounds, or switch the SCOPE palette (Daylight, Obsidian, Phosphor, Blueprint).

📐 Corner Grip Resizing (`720 × 450` to `3840 × 2160`)

Drag the bottom-right three-line grip to resize Scopion smoothly to any size. Hold Shift while dragging to lock the 1040 : 640 aspect ratio, or double-click the corner grip anytime to snap straight back to 100%. Extra wide window space expands the plot canvas automatically.

4. Four Selectable Scope Color Schemes

Switch the recessed measurement stage live between four high-contrast palettes while keeping the warm Nordic Daylight outer frame intact — every palette carries directly into PNG and SVG exports:

Daylight — Porcelain Paper (default print-ready light stage)

Obsidian — Dark Studio OLED stage

Phosphor — Classic Tektronix P31 CRT aesthetic

Blueprint — Cyan Technical Grid on Midnight Navy

5. Coordinate Plot Navigation & Shortcuts

Action	Gesture / Control
Pan Viewport (2D)	Left-click + drag anywhere inside the plot, or drag the bottom H and right V scrollbars.
Zoom Both Axes Around Cursor	Mouse Wheel inside the coordinate plot.
Zoom Horizontal Axis Only	`Shift` + Mouse Wheel inside the plot, Mouse Wheel over the H bar, or click `-` / `+` on the H bar.
Zoom Vertical Axis Only	`Ctrl` + Mouse Wheel inside the plot, Mouse Wheel over the V bar, or click `-` / `+` on the V bar.
Reset Viewport (`A`)	Double-click inside the plot, click the `A` button in the bottom-right plot corner, or click `Reset` in Row 2.
Precision Curve Readout	Hover anywhere inside the plot for exact cursor coordinates (`Time [s]` / `Amplitude` + `dBFS` in `SIGNAL`; `Frequency [Hz]`, musical note/cents, cursor `dB`, and interpolated `L`, `R`, `Ref` levels in `SPECTRUM`).
Context Menu	Right-click inside the plot to Freeze/Unfreeze, Reset Zoom, toggle `CH L` / `CH R`, Capture/Clear `REF`, pick Window Size presets (`75%–200%`), or open Export Plot....

6. Exporting Plots (`PNG` & Vector `SVG`)

Click Export in the top-right header (or right-click the plot and choose Export Plot (PNG / SVG)...) to generate crisp studio graphs:

Custom Resolution (Width × Height): Defaults to the live logical plot size and scales cleanly from 320 × 180 up to 7680 × 4320 (8K).
Format (PNG / SVG):
- PNG: Renders an anti-aliased RGBA bitmap using Xiaolin Wu sub-pixel line rasterization, filled spectrum curtains, dashed REF overlays, and axis labels.
- SVG: Generates a resolution-independent vector document with <polyline> traces, stroke-dasharray="6,4" reference lines, and sharp <text> labels.
Target File (Browse...): Choose a destination path; switching between PNG and SVG updates the filename extension automatically.
Apple Logic Pro On-Screen Keypad (macOS): When hosted inside Apple Logic Pro, GarageBand, or MainStage, clicking any text box in the Export modal automatically opens a floating mouse-clickable QWERTY & numeric pad so DAW transport key-hijacking never blocks export naming or dimensions.

7. Four Studio Measurement & Mixing Recipes

Use these proven setups to diagnose phase, sub-bass headroom, and tonal balance in seconds:

Low-End / EDM & Pop

1. Kick & Sub-Bass Phase Alignment

Verify whether your kick tail and sub-bass fundamental reinforce or cancel each other out at the crossover point.

Setup: Mode: SIGNAL • Trigger: 30 Hz ZEROS • Time Span: 20 ms – 45 ms

Workflow: 1) Solo Kick -> click REF to store snapshot • 2) Solo Sub-Bass -> compare live trace against dashed REF

Goal: Align polarity/delay until rising peaks line up constructively at t = 0 ms.

Mastering / Bus

2. Mastering Headroom & Sub-Sonic Check

Spot silent 15–35 Hz rumble, DC offset, or sharp resonant whistling spikes robbing limiter headroom.

Setup: Mode: SPECTRUM • FFT Length: 16384 or 32768 • Scale: LOG

Workflow: Zoom vertically to -96 dB .. +6 dB and hover peaks for exact Hz + musical pitch note/cents readout

Goal: Confirm sub-30 Hz energy rolls off cleanly and check CLIP LED on the top Stereo Input Monitor.

Mixing / Reference

3. Mix Reference A/B Spectral Match

Compare the tonal curve of a commercial reference master directly against your own mix bus in real time.

Setup: Mode: SPECTRUM • FFT Length: 8192 • Scale: LOG • CH L + CH R active

Workflow: Play reference track -> press FREEZE + REF • Switch back to your mix -> enable live trace over dashed REF

Goal: Match low-mid warmth (150–400 Hz) and air (8–16 kHz) visually without guessing.

Docs / Teaching

4. Publication-Grade Vector Figures

Generate crisp, glare-free waveform and harmonic diagrams for studio notes, bug reports, or tutorials.

Setup: Theme: Daylight (print) or Blueprint (slides) • FREEZE active for rock-solid capture

Workflow: Click Export (or right-click plot) -> choose SVG for infinite zoom or PNG up to 7680 × 4320 (8K)

Goal: Includes CH L, CH R, dashed REF traces, axis ticks, and sub-pixel Xiaolin Wu anti-aliasing.

8. DAW Plugin Installation & Linux Standalone Application

Linux (x86_64) — Plugins & Standalone

Copy scopion.clap to ~/.clap/ and scopion.vst3 to ~/.vst3/.

Standalone App: Copy scopion to ~/.local/bin/scopion (or /usr/local/bin/scopion) and run chmod +x.

Windows (x86_64) — DAW Plugins

Copy scopion.clap to C:\Program Files\Common Files\CLAP\ and scopion.vst3 to C:\Program Files\Common Files\VST3\, then rescan in your DAW.

macOS Universal2 (Apple Silicon & Intel)

Copy Scopion.component (Logic Pro AUv2) to ~/Library/Audio/Plug-Ins/Components/ and Scopion.clap to ~/Library/Audio/Plug-Ins/CLAP/, then run once in Terminal:
xattr -dr com.apple.quarantine ~/Library/Audio/Plug-Ins/Components/Scopion.component ~/Library/Audio/Plug-Ins/CLAP/Scopion.clap

Linux Standalone Monitor Routing (`scopion`)

Silent Output Guarantee: In standalone mode, Scopion zeroes its playback output buffer right after tapping incoming audio so system audio is never doubled or echoed back to your speakers.
Automatic PipeWire Output Tap: Launched without custom input flags on PipeWire, Scopion queries @DEFAULT_AUDIO_SINK@ via wpctl and links your active interface's stereo monitor ports (:monitor_FL/:monitor_FR or Pro-Audio :monitor_AUX0/:monitor_AUX1) straight into alsa_capture.scopion:input_FL and input_FR.
ALSA CLI Options: Run scopion -b alsa --input-device default -p 1024 for explicit ALSA device selection, or scopion -b alsa --input-device "" to list available devices.

9. Complete Parameter & View State Reference

Every automatable DAW parameter and persisted view state in Scopion:

ID	Name	Section	Type	Default	Range	Unit	Description
display	Display Mode	Header	Enum	`Signal`	Signal / Spectrum	—	Switches between Time-Domain Oscilloscope (SIGNAL) and Calibrated Hann FFT Analyzer (SPECTRUM).
sync	Trigger Sync	Signal	Enum	`Free Running`	Free Running / Lowpass Zeros	—	Toggles continuous rolling window vs. 30 Hz Butterworth sub-sample rising zero-crossing sync.
method	Spectrum Method	Spectrum	Enum	`Fourier Transform`	Fourier Transform	—	Active single-pass stereo Radix-2 Cooley-Tukey f64 FFT engine.
fft_size	FFT Length	Spectrum	Enum	`8192`	256, 512, 1024, 2048, 4096, 8192, 16384, 32768	samples	Selects transform resolution from fast transient tracking (256) to razor-sharp sub-Hz bass separation (32768).
log_scale	Frequency Scale	Spectrum	Bool	`Log (On)`	Log / Lin	—	Switches horizontal spectrum axis between Logarithmic (15.625 Hz – 32 kHz) and Linear (0 Hz – Nyquist).
freeze	Freeze Buffer	Header	Bool	`Off`	Off / On	—	Latches the 262,144-sample (~5.4 s at 48 kHz) lock-free ring buffer for detailed zoom and export.
show_left	CH L Visibility	Stage	Persisted Toggle	`On`	On / Off	—	Toggles or solos the Left channel trace in both SIGNAL and SPECTRUM modes.
show_right	CH R Visibility	Stage	Persisted Toggle	`On`	On / Off	—	Toggles or solos the Right channel trace in both SIGNAL and SPECTRUM modes.
ref_trace	REF Memory Trace	Stage	Snapshot	`Empty`	Capture / Toggle / Clear	—	Stores both stereo time-domain and FFT snapshots for dashed A/B comparison across zoom and mode switches.
color_scheme	Scope Color Scheme	Stage	Persisted Selector	`Daylight`	Daylight, Obsidian, Phosphor, Blueprint	—	Selects the recessed plot stage palette live on screen and in PNG/SVG exports.
signal_range	Signal Viewport	View State	Persisted Bounds	`-2.75..55 ms / ±1.5`	Up to 1.50 s / ±1.5	s / amp	Saved horizontal time span and vertical linear amplitude bounds for SIGNAL mode.
spec_range	Spectrum Viewport	View State	Persisted Bounds	`15.625 Hz..32 kHz / -96..+6 dB`	Log & Lin bounds	Hz / dB	Saved Log/Lin frequency bounds and decibel floor/ceiling for SPECTRUM mode.
editor_state	Window Scale & Size	UI State	Persisted Size	`1040 × 640 (100%)`	720 × 450 to 3840 × 2160 (75%–200% presets)	px	Proportional window sizing via header scale dropdown, plot context menu, or Shift+Drag corner grip.

Scopion Manual & Reference Guide

1. Visual Overview