#gFractor — User Manual

This is the end-user manual for gFractor 1.2.3, a multi-mode spectrum analyzer, oscilloscope, waterfall, and metering plugin from GrowlAudio. It assumes you're an audio engineer or producer who already knows what FFT, mid/side, slope tilt, transients, and phase correlation are.

#1. What gFractor is

A measurement plugin (VST3 / AU / Standalone) you put on any bus to see what's in your audio. It offers three views — a spectrum analyzer, a tempo-synced oscilloscope, and a scrolling waterfall (reassigned spectrogram) — over four channel decompositions (Mid/Side, Left/Right, Tonal/Transient, and L+R mono-sum), with a goniometer + correlation + correlation-per-octave metering panel and a full ITU-R BS.1770-4 LUFS meter alongside. It does not colour the audio unless you tell it to: a gain stage, a dry/wet mix, and the audition filters are the only signal-path controls — plus reference mode, which swaps the sidechain in for the input (section 8).

VST3 and Standalone run on macOS, Windows, and Linux; AU is macOS-only.

Insert it post-fader on a master bus or any group whose tonal/stereo balance you want to monitor. The analyzers read the signal entering the plugin; only the LUFS meter reads what leaves it.

#2. Quick start

1. Load gFractor on a bus and play audio.
2. Two coloured spectrum curves animate in real time. By default:
   • Green is the Primary channel (Mid in M/S mode, Left in L/R, Transient in T/T).
   • Amber is the Secondary channel (Side, Right, or Tonal).
3. Press Tab to cycle the channel decomposition: M/S → L/R → TRN → M/S… The pill captions in the footer rename themselves to match (MID|SIDE, LEFT|RIGHT, TRANS|TONAL). The fourth mode, L+R mono-sum, is selected from the footer Mode dropdown (Tab cycles only the first three — see section 3).
4. Press V to cycle the view: Spectrum → Oscilloscope → Waterfall → Spectrum…
5. Click STEREO in the footer to slide out the right-side metering panel (goniometer, correlation, correlation per octave). Click LUFS for the loudness meter. (Only one of the two can be open at a time.)
6. Hover the spectrum to read frequency / dB / nearest musical note. Right-click and drag to audition a bell filter (drag vertical for Q).
7. Press E (or the camera pill in the header) to save a PNG of the current view.
8. Optional: turn on Piano Keys in Preferences → Display to get a pitch-aligned keyboard under the spectrum that highlights the key you're hovering.

That's the whole product, conceptually. The rest of this manual explains each piece.

#3. The Primary / Secondary concept

gFractor's most important UI decision: the same two channel toggles, the same two curves, and the same two colours are reused across all channel modes. They are always labelled Primary (green) and Secondary (amber) internally — only the captions change.

A few consequences:

• Each channel pill has two zones. The label (and keys 1 / 2) toggles the visibility of the green and amber traces — it only affects what you see. The speaker icon on the left of the pill (and Shift+1 / Shift+2, or Shift/Alt-click anywhere on the pill) mutes that channel in the audio output.
• In L+R mode there is only one lane: both channels are summed into a single Primary trace and the Secondary pill is hidden. Useful for a quick mono-compatibility check or a clutter-free view.
• The Reference / Ghost / Target overlays use different colours (blue and pink) to avoid collisions, so you can run a reference comparison without losing track of which curve is which.

About Tab: the keyboard cycle steps through the first three modes only (M/S → L/R → TRN). To reach L+R, pick it from the footer Mode dropdown.

The T/T mode is worth a separate note: it uses a per-sample dual-envelope tracker (fast vs slow envelope, normalised by body level), not an FFT, so it adds no latency — gFractor always reports 0 samples. The Transient curve emphasises percussive content; the Tonal curve emphasises sustained content. Adjust the time constant in Preferences → Analyzer → Trans Len (default 1.0 ms; range 0.1–10 ms).

#4. Interface tour

      +-------------------------------------------------------------+
      |  HEADER  g/Fractor • by GrowlAudio [Preset][CAM][SETTINGS][Help]
      +-------------------------------------------------------------+
      |                                                |            |
      |                                                | Stereo /   |
      |  VIEW AREA   Spectrum / Oscilloscope /         | LUFS panel |
      |              Waterfall                          | (sliding)  |
      |                                                |            |
      +-------------------------------------------------------------+
      |  FOOTER    [SPEC▾] [M/S▾] [MID] [SIDE]  [REF] [GHOST] [FREEZE]
      |            (spectrum) [HOLD] [SAVE] [LOAD] [TARGET]          |
      |            [LUFS] [STEREO]                                   |
      +-------------------------------------------------------------+
      |  HINT BAR  hover hints       [FFT▾][Ovr▾][Dec▾][Slp▾][Smo▾] |
      +-------------------------------------------------------------+
      

#Header bar

• Preset pill — shows the current preset name, with a dot if the state is dirty. Click for the preset menu.
• Camera pill — saves a PNG of the current view (section 10). Same as E.
• SETTINGS — opens the Preferences overlay (section 12).
• Help — About gFractor, Check for Updates, Manual, and (in standalone) Audio Settings. When a newer version exists, the menu reads Update available: version and a small dot appears on the button.

#View area

The main display. One of three views renders here — Spectrum, Oscilloscope, or Waterfall — cycled with V or the footer view dropdown (SPEC / SCOPE / WTF). Press W in spectrum mode to expand the view fullscreen across the footer/hint bar.

#Footer bar

The control surface. Most footer pills are toggles; a few (View, Channel Mode, Vertical Scale, Time Window, and the Waterfall pills) are dropdowns. Pill captions on the left depend on channel mode; pill availability depends on which view is active — spectrum, oscilloscope, and waterfall each show their own set. REF and GHOST are greyed out until a sidechain is connected.

#Hint bar

The bottom strip is contextual: hover over any control or the spectrum/scope itself, and the hint bar shows what you can do there (e.g. CLICK | DRAG — Audition band | Move between bands). On the right, in spectrum mode, you also get five global dropdowns for FFT size, Overlap, Decay, Slope, and Smoothing.

#Right-side panels

The Stereo and LUFS pills each slide out a panel on the right edge. They share the right column, so only one can be open at a time — opening one closes the other. Drag the vertical divider on the left edge of the panel to resize. Which panel is open, and its width, are remembered.

#5. The Spectrum view

A real-time FFT magnitude spectrum, log- or linear-frequency × dB, with 256 log-spaced render points across the visible range. Both Primary and Secondary curves are drawn simultaneously and can be overlaid with Ghost (sidechain), peak Hold, and Target curves.

#Analysis parameters (hint-bar dropdowns)

The frequency scale (Log or Linear) is set in Preferences → Analyzer → Freq Scale, not the hint bar. Log is the classic view; Linear is handy for inspecting harmonic spacing.

Cmd+wheel (macOS) / Ctrl+wheel (Windows/Linux) over the spectrum zooms the dB axis about 0 dB. The new range is saved to your preferences, the same as setting Min/Max dB by hand.

#Persistence controls (footer)

• FREEZE (key Z) — pauses the display without stopping audio analysis. Useful for taking a screenshot of a transient. Freeze applies to whichever view is active.
• HOLD (key H) — infinite peak hold. Adds a glow trace at the maximum bin levels seen since enabled. Disable + re-enable to reset.

#Ghost, Target, Audition

• GHOST (key G) — draws the sidechain signal as a second, dimmer pair of curves (in the reference colours) under the main ones, so you can compare two sources without switching anything. Needs a sidechain (section 8); the pill is greyed out without one. On by default, and saved with the preset.

• REF (key R) — reference mode: the sidechain replaces the main input. See section 8.

• Target curves — capture a peak-hold curve, save it, and overlay it later:

  1. Turn on HOLD and play the material you want to capture.
  2. SAVE (enabled only while HOLD is on) writes both peak-hold curves — Primary and Secondary — to a .json file.
  3. LOAD reads a curve file back; it appears as a dashed overlay and TARGET turns itself on.
  4. TARGET (key T) shows or hides the loaded curve. It stays greyed out until a curve is loaded.

  Typical use: capture the spectrum of a reference master, save it, then load it over your own mix.

• Right-click drag on the spectrum — auditions a resonant bell filter on the audio path at the cursor frequency. Horizontal drag sweeps frequency, vertical drag adjusts Q (0.5–10, default 4). Release to remove. Useful for confirming a resonance by ear.

#Band audition strip

Just above the frequency axis, gFractor draws a thin clickable strip with seven musical band labels: Sub (20–80 Hz), Low (80–300), Low-Mid (300–600), Mid (600–2000), Hi-Mid (2000–6000), High (6000–12000), and Air (12000–20000 Hz). Audition a band to hear a problem frequency in isolation:

• Click a band to solo it (band-pass) while the mouse is held.
• Cmd-click (macOS) / Ctrl-click (Windows/Linux) to latch the band so it stays active after you release.
• Right-click a band to cut it instead — a notch (band-reject) rather than a solo.
• Drag along the strip to move between bands without releasing.
• A plain click anywhere else in the spectrum clears a latched band and resets the curves.

Solo and cut are visually distinct — a blue accent with solid boundaries for solo ("keep"), a warm red with dashed boundaries for cut — and the styling is colour-blind friendly. These filters act on the audio output, which is what makes them audible. The strip can be hidden with Preferences → Display → Band Hints.

#Hover readout and crosshair

Move the pointer over the spectrum and a crosshair tracks it. The crosshair is drawn whether or not Show Tooltip is on — that setting governs only the intersection dots on the curves and the freq/dB/note balloon. Turn it off when you want an uncluttered display but still need to line a frequency up by eye.

#Piano keyboard

An optional keyboard strip under the spectrum, frequency-aligned with the plot so each key sits at its own pitch on the axis. Enable it in Preferences → Display → Piano Keys; it is off by default. Hovering the plot marks the key under the cursor and carries the crosshair down to it, giving you the pitch of whatever you're pointing at without reading the tooltip. The strip is drawn dimmed so it never outshines the curves.

#Reference guidelines

Up to six horizontal reference lines can be drawn over the spectrum, each with its own colour, label, anchor level, and slope from −12 to +12 dB/oct — so a guideline can be a tilted target contour (a −4.5 dB/oct pink-noise curve, say) rather than a flat level. Add, remove, and configure them in Preferences → Guidelines (section 12).

#Split spectrum

Press X in spectrum mode (or toggle Preferences → Display → Split Spectrum) to stack the channels — Primary in the top half, Secondary in the bottom half — so you can compare them without overlap.

#Fullscreen

Press W to hide the footer + hint bar and expand the spectrum across the entire window. Press W again to restore.

#6. The Oscilloscope view

Press V until the oscilloscope shows. Tempo-synced time-domain waveform of Primary and Secondary, with the cursor tracking DAW playback position.

An optional CRT filter (Preferences → Display) gives the trace a warmer, more analog feel, paired with a denser grid graticule.

#Pan and zoom

• Mouse wheel over the scope — horizontal zoom, centred on the pointer.
• Horizontal drag (or a horizontal trackpad swipe) — pan the time window when zoomed in.
• Scrollbar — once you're zoomed in, a horizontal scrollbar appears under the trace showing which slice of the window you're looking at. Drag it to pan, as an alternative to dragging the waveform itself.

With the transport running, the sweep stays synced to the host: it keeps drawing on loops shorter than the time window, and blanks past the loop boundary rather than smearing stale samples across the turnaround — including while zoomed.

#Ghost / Reference in the scope

• GHOST (key G) draws the sidechain as a desaturated, filled envelope beneath the main curves, sample-aligned with them — useful for checking a kick against a bass, or pre against post on the same musical moment. Needs a sidechain.
• REF works here too: the scope shows the sidechain signal in the reference colours (section 8).

#7. The Waterfall view

Press V until the waterfall shows — a scrolling reassigned spectrogram. Energy is snapped to its true time–frequency location, so a pure tone paints a single crisp line instead of a smeared band, making harmonics, sidebands, and transients far easier to read. Frequency runs along one axis, time scrolls, and level is mapped to colour (range fixed at −100 to 0 dB).

The waterfall has its own footer pills (the channel-mode, channel, REF, and GHOST controls are hidden in this view):

The shared FREEZE (key Z) pauses the waterfall so you can study a moment in detail.

#8. Reference mode (sidechain A/B)

Reference mode lets you A/B against any signal routed to gFractor's sidechain input. With REF on, the sidechain replaces the main input for the whole chain: the analyzers, the channel split, the audition filters, and the LUFS meter all act on the reference, and the curves switch to the reference colours (blue / pink).

Important: because the sidechain replaces the input, gFractor's audio output becomes the sidechain signal while REF is on. Use reference mode on a monitoring/analysis insert (or the last slot on your master, where hearing the reference is the point), not in the middle of a live mix path.

If you want to see the reference without hearing it, use GHOST instead (section 5) — it overlays the sidechain as a dimmer second pair of curves and leaves the output alone.

#Routing the sidechain

#Using reference

• REF (key R) — latching toggle.
• Hold Ctrl — momentary reference: REF is on only while held. Useful for fast A/B without taking your hand off the keyboard.

REF and GHOST are greyed out until a sidechain is connected. REF is never saved: it switches off when you close the plugin window, so a session never reopens silently playing the reference. In standalone mode there is no sidechain, so both stay inert.

#9. Metering panels

The footer's right side has two pills — STEREO and LUFS. They share the right column, so opening one closes the other.

#Stereo metering panel

Click STEREO to open. Three instruments, top to bottom:

#Goniometer

A 45°-rotated Lissajous of L vs R with phosphor persistence. Reads the same way as any classical vectorscope:

• A vertical line = mono content.
• A wide diamond = strong stereo content with good phase.
• A horizontal line = out-of-phase (mono-collapse will cancel).

#Correlation meter

A horizontal bar from −1 to +1. Useful at-a-glance check: stays around +0.4 to +0.9 for healthy stereo; dipping toward 0 or below 0 on a mix bus is a phase warning.

#Correlation / Oct

L/R correlation per octave band, across ten ISO octave bands from 31.5 Hz to 16 kHz. A broadband correlation number is energy-weighted, so a loud in-phase midrange hides an anti-correlated sub: a 40 Hz polarity error under an in-phase 2 kHz reads −0.00 on the broadband bar. The per-band chart shows exactly which octave is out of phase. The analysis runs on an 8192-point FFT so the 31.5 Hz band is actually resolved, and a band with no energy reads zero rather than painting a confident bar off noise.

#LUFS panel

Click LUFS to open the loudness meter. ITU-R BS.1770-4 / EBU R128 compliant. Unlike the rest of gFractor, it measures the plugin's output.

• The bar shows short-term loudness, with the integrated value marked by an amber tick on the same axis. The scale defaults to a mastering-range −15 to +2 LUFS; set it with LUFS Min / LUFS Max in Preferences → Meters.
• Six readouts: Short Term, Integrated, Loudness Range (EBU Tech 3342), Dynamics (PSR — peak minus short-term), Avg Dynamics (PLR — peak max minus integrated), and Crest — the plain, unweighted peak-to-RMS ratio in dB over the same 3 s window as the peak. PSR and PLR measure peak against a K-weighted loudness; crest reads the waveform's shape instead, so a signal can be squashed in one sense and not the other.
• Three max trackers: Momentary Max, Short Term Max, Peak Max. Click one to mark it on the bar.
• Reset clears the integrated value, loudness range, and the max trackers.

#LUFS or LU

The LUFS / LU pills above the meter switch the loudness numbers between absolute LUFS and LU relative to a target: against the default −23 LUFS target, a −14 LUFS programme reads +9 LU. Short Term, Integrated, and the loudness max trackers follow the switch; Loudness Range and the dynamics rows are differences already, and Peak Max is a sample peak, so those never change unit.

In LU the bar's scale is drawn in LU too, and the target is marked on it as a dashed line at 0 LU, captioned with the absolute level it stands for. When the target falls outside the scale range, the caption pins to the nearest end of the bar with a caret pointing the way it lies. A TARGET badge next to the pills names the level; drag it vertically to retarget in 0.5 LU steps. The target (−40 to 0 LUFS), the scale range, and the LUFS/LU choice are global preferences, remembered across projects.

#Reset on play

Preferences → Meters → Reset On Play restarts the loudness measurement whenever the host transport starts rolling, so each playback pass is measured on its own. Stopping changes nothing — the numbers stay up to be read, and only the next start clears them. Off by default, in which case the measurement runs until you press reset. Only the stopped → rolling transition triggers it, so a pass that keeps playing is never interrupted, and a host that reports no transport at all (some offline renders) never resets. It applies while the plugin window is open.

#10. Exporting a PNG

Press E, or click the camera pill in the header, to save a picture of the current view. gFractor renders it at a fixed 2× regardless of UI scale, adds a caption strip — the logo, the version, the view and channel mode, and for the spectrum the FFT size, slope, and dB range — then reveals the file.

Files are named gFractor-YYYYMMDD-HHMMSS.png and go to a gFractor folder in your Pictures folder (macOS ~/Pictures/gFractor, Windows Pictures\gFractor, Linux $XDG_PICTURES_DIR/gFractor). If there's no Pictures folder, gFractor falls back to the Desktop, then your home folder.

Export is unavailable while the Preferences overlay is open — close it first.

#11. Presets

Click the preset pill in the header to open the menu.

• Init — loads the default state (always available).
• User presets — click any saved preset to load it; the current one is checked.
• Save Preset... — prompts for a name and writes the current state (overwrites if the name exists).
• Delete "name" — removes the active user preset after a confirmation (disabled on Init).

User presets are .xml files in your user application-data folder:

A dot next to the preset name indicates the state is dirty — a parameter or a saved display setting has changed since the preset was loaded. Loading another preset, saving, or loading Init clears the dot.

#What a preset stores

A preset saves the plugin parameters plus the display/view state — channel mode, view mode, Primary/Secondary/Ghost visibility, vertical scale, time window, spectral coloring, the waterfall FFT/colour/scroll/reassign settings, and the spectrum's FFT / overlap / decay / slope / smoothing.

What a preset does not store — these are global per-user and apply across all instances: the Preferences-panel settings (trace colours, dB/Hz ranges, frequency scale, theme, UI scale, brightness, fill mode, split toggles, tooltip, scope dB cursor, band-hint and piano-key toggles, reference guideline lines (including their per-line slopes), curve order, the LUFS meter scale / LU target / LUFS-or-LU choice / Reset On Play, analytics consent, and keyboard shortcuts), plus window size, which metering panel is open and its width, and the daily update-check cache.

#12. Settings (Preferences)

Click the SETTINGS pill in the header. A modal panel overlays the view, organised into seven tabs: Analyzer, Traces, Guidelines, Display, Meters, System, Keys. Within each tab the rows are grouped into framed cards by topic.

#Analyzer

#Traces

#Guidelines

Configurable horizontal reference lines on the spectrum — handy for marking target levels and target contours. Add and remove lines here, up to six.

Slopes are stored per line and persisted with the rest of your global preferences. Setups made before 1.2.2 keep the old fixed 0 / −3 / −4.5 / −6 dB/oct lines, so nothing shifts under you on upgrade.

#Display

#Meters

#System

#Keys

A master Shortcuts On/Off switch (disable if the DAW eats keystrokes), plus a remappable list of every keyboard action — click a row and press the key you want.

Save commits all changes; Cancel discards them; Reset restores factory defaults — including the trace colours. Esc closes the panel.

Note: only gain, dryWet, bypass, outputPrimaryEnable, outputSecondaryEnable, and transientLength are exposed as DAW-automatable parameters. The Preferences settings above are user-global, not per-session — they apply across all instances of the plugin and are not stored in presets or session state.

#13. Keyboard shortcuts

Shortcuts can be globally disabled — and individually remapped — in Preferences → Keys. These are the defaults.

#Channel

#View

#Display overlays

#Spectrum parameter cycling

Smoothing has no default key — use the hint-bar dropdown, or bind one in Preferences → Keys.

#Misc

#Mouse

#14. Standalone & About

gFractor ships as a standalone app alongside the VST3 and AU plugins. The standalone window uses the native OS title bar, and audio device settings live in the Help menu (Audio Settings...).

The Help menu also opens a custom About gFractor dialog — the gFractor brand mark, a link to growl-audio.com, and credits, rendered as a native overlay that matches the rest of the interface. (There may be a little something hidden in there for the curious.)

#15. Troubleshooting

REF and GHOST are greyed out. No sidechain is routed. See section 8 for your DAW's sidechain setup. In standalone mode there is no sidechain, so both stay inert.

The audio changes when I turn on REF. Expected — reference mode feeds the sidechain through the whole chain, output included. Use GHOST to compare without changing the output, or put gFractor on an analysis insert.

Pressing Tab / R / Z etc. does nothing. Either the plugin window doesn't have keyboard focus (click anywhere inside it first), your DAW captures the key before gFractor sees it (common with Tab in Live and Pro Tools), or shortcuts are switched off in Preferences → Keys. Workaround: change modes via the footer dropdowns, or remap the shortcut.

Tab won't switch to L+R mono mode. That's expected — Tab cycles only M/S → L/R → TRN. Select L+R from the footer Mode dropdown.

A band stays soloed. You Cmd/Ctrl-clicked it, which latches. Click anywhere in the spectrum body to clear it.

SAVE is greyed out. SAVE writes the peak-hold curves, so it only works while HOLD is on.

Spectrum looks coarse at the low end. Increase FFT size (key F). Below 80 Hz, frequency resolution is limited by the FFT and a smaller size won't resolve adjacent bass notes.

Spectrum is choppy. Increase Overlap (key O) and/or set Decay to Slow (key D). If CPU is the constraint, drop the FFT size.

Plugin uses high CPU. The biggest cost factors are FFT × Overlap. Try 4096 / 4× as a baseline; reserve larger sizes / 8×–16× for static-track analysis. Gradient fill and High-DPI Spectrum also cost more — switch Fill to Solid/No Fill, turn on Simplify Curve, or turn High-DPI off if needed. The oscilloscope, waterfall, and metering panels are comparatively cheap.

The spectrum shows my input, not my processed output. By design — everything except the LUFS meter analyzes the signal entering the plugin. Place gFractor after whatever you want to measure.

The LUFS numbers reset every time I press play. Preferences → Meters → Reset On Play is on. Turn it off to keep one measurement running until you press reset.

E doesn't export a PNG. Close the Preferences overlay first — export is refused while it's open.

Preset state didn't recall correctly. Presets store plugin parameters plus display/view state (channel mode, view, FFT/overlap/decay/slope/smoothing, waterfall settings). They do not store Preferences-panel settings (trace colours, dB/Hz ranges, frequency scale, theme, UI scale, brightness, meter settings, etc.) — those are global per-user. If something didn't recall, check whether it's a Preferences setting rather than a preset value.

The Help button has a small dot on it. A newer version of gFractor is available — the Help menu shows Update available: version. Click it to open the download page.

Update check failed / I want to disable it. The check hits growl-audio.com/plugins/gfractor/version.json at most once per calendar day on a worker thread. No telemetry is sent. There is no UI toggle to disable the check itself; if you need to block it, block the domain at your firewall.

gFractor 1.2.3 — © GrowlAudio. Built with the JUCE Framework.