Aetherial Parametric EQ (TX / RX) overview

The Aetherial Parametric EQ provides client-side parametric equalization for both your transmit and receive audio paths. Use it to shape your TX microphone audio or to tailor the sound of received audio before it reaches your speakers or headphones, without touching any radio-side processing.

Before you start

• AetherSDR must be running. A radio connection is not required to configure the EQ, but a connection is needed for the live FFT analyzer overlay to show real audio.
• The EQ applet tiles are hidden until the matching EQ stage is enabled via the CHAIN widget or the floating editor. If you do not see "Aetherial TX EQ" or "Aetherial RX EQ" in the Aetherial Audio (TXDSP) parent container, enable the EQ stage first.

How it works

AetherSDR instantiates two separate EQ tiles inside the Aetherial Audio (TXDSP) parent container:

• Aetherial TX EQ — processes audio on the transmit path only.
• Aetherial RX EQ — processes audio on the receive path only.

Each tile is fixed to its path. There is no in-tile RX/TX selector. The tile shows a compact view of the summed EQ response curve and a live FFT analyzer overlay for that path. A peak-hold trace is drawn on top of the live analyzer, showing the per-frequency maximum level seen since the last reset; the trace decays at approximately 10 dB/sec during normal operation. The peak-hold trace operates on raw FFT bins so peak detection is sample-accurate; display smoothing (when enabled) is applied separately and does not affect the peak-hold data. Editing — adding, removing, and tuning bands — happens in a separate floating window called the Aetherial Parametric EQ editor, which opens from the CHAIN widget. The editor's title bar reads either "Aetherial Parametric EQ — TX" or "Aetherial Parametric EQ — RX" depending on which side you opened it from. One shared editor instance is reused for both sides; the title flips when you switch sides.

Applet tile

Each tile contains one control area:

Element	Description
Analyzer / curve area	A minimum 110 px tall view showing the summed EQ response curve for all enabled bands on that path, with a live FFT analyzer overlay and a peak-hold trace. Dashed yellow vertical lines mark the radio's current TX low/high filter cutoffs (TX tile) or RX passband edges (RX tile). This area is view-only in the applet tile.

The summed EQ response displays the cumulative frequency response of all enabled bands. When no bands are boosted or cut, the curve is flat; it dims to grey when the EQ stage is bypassed. The live analyzer overlay shows the real-time FFT of audio passing through that path as a cyan gradient fill; it is idle when no audio is active and running when audio is present. The peak-hold trace is a soft off-white line that tracks the per-frequency maximum energy observed, helping you identify resonances and harsh peaks while tuning. The trace decays at approximately 10 dB/sec between updates. It can be frozen from the floating editor using the Peak Hold button. The filter cutoff guide lines are dashed yellow vertical lines that mark the radio's current TX low/high filter cutoffs (TX tile) or RX passband edges (RX tile) directly on the canvas. These lines are visible in the applet tile and are draggable in the floating editor. An audio band-plan strip is always visible at the bottom of the canvas showing E-SSB / SSB / AM-FM modulation regions as a reference; cursor interaction in this area is excluded from band-handle hit-testing.

Floating editor

Double-clicking the EQ stage in the CHAIN widget opens the floating editor for that side. The editor provides:

Control	Description	Notes
Analyzer / curve area (canvas)	Interactive canvas where you drag band handles to set frequency and gain. Drag peak/shelf handles to adjust frequency and gain. Drag HP/LP handles to adjust frequency and Q. Hold Shift while dragging to adjust Q on any band type. Click a band icon to cycle through filter types. The peak-hold trace is visible here as well and reflects the frozen/decaying state set by the Peak Hold button. The canvas also shows a semi-transparent amber reference curve overlay and dashed yellow radio filter cutoff guide lines.	The docked applet tile shows a minimum 110 px tall view with the same summed response, live FFT analyzer, and peak-hold trace, but is view-only; editing happens in the floating editor. The editor canvas is part of a frameless window.
Ref (reference curve overlay)	Combo box in the editor header strip. Overlays one of several target frequency-response curves on the EQ canvas as a thin amber line, as a visual guide while you tune bands. Options: Off, AT&T 1959, Heil DX, Astatic D-104, Shure 444, Heil HC-5. Includes the AT&T 1959 Bell Labs intelligibility target plus digitised responses of famous SSB microphones (Astatic D-104, Shure 444, Heil HC-5) and a Bob-Heil aggressive DX preset.	Display-only — the overlay does not affect EQ math. Persisted globally (single user preference shared between RX and TX editors) as ClientEqReferenceCurve. Located in the floating editor header strip and the Channel Strip EQ panel, not the docked applet tile.
Smoothing	Combo box in the editor header strip. Applies fractional-octave power-averaging to the analyzer trace for display — does not affect EQ math. Options: Off (1/96), 1/24, 1/12, ⅙, ⅓. Default: Off (1/96). Lower fraction = smoother (⅓ is most smoothed; 1/96 is effectively off). Shared between TX and RX editors. Persisted as ClientEqSmoothingFraction.	Tooltip: "Fractional-octave smoothing applied to the analyzer trace. Lower fraction = smoother (⅓ = most, 1/96 = off). Affects display only — EQ math is unchanged." Located in the editor header strip (floating editor only). Smoothing is computed after the peak-hold update each frame, so both the live trace and the peak-hold trace are smoothed independently for display.
Peak Hold	Toggle button in the editor header strip. When checked, the analyzer's per-bin peak-hold trace stops decaying — every frequency's highest observed level is held until you toggle the button off. The button shows an amber background when checked. Toggle off to resume normal decay at approximately 10 dB/sec.	Located in the editor header strip (floating editor only).
Filter family	Combo box in the editor header strip. Selects the filter family applied to HP/LP cascade math. Options: Butterworth (maximally flat passband), Chebyshev (steeper transition, 1 dB passband ripple), Bessel (linear phase, gentler rolloff), Elliptic (steepest transition, ripple in both bands). Default: Butterworth. Shelves and peaks use their native second-order topology regardless of this setting. Persisted separately per path: ClientEqTxFilterFamily / ClientEqRxFilterFamily.
Reset	Push button in the editor header strip. Drops every band back to default values, restores the default 10-band count, and resets the filter family to Butterworth. Saves immediately. Tooltip: "Reset all bands to default values".	Located in the editor header strip (floating editor only).
Filter-type icon row	A row of 8 custom-painted icons (one per band slot) at the top of the editor canvas area. Each icon draws the current filter shape (peak bell, shelf ramp, HP/LP slope) in its band's palette colour. Click an icon to cycle through the filter types for that band; clicking also selects the band, highlighting its handle on the canvas and its column in the parameter row.	Located in the floating editor only. Icons dim to 35 % opacity when the band is bypassed. Implemented by ClientEqIconRow.
Parameter text row	A row of 8 text columns (one per band slot) below the canvas showing each band's Freq, Gain, and Q values. Values update live during canvas drags. Clicking a column selects that band. Right-click a column to open a context menu for numeric entry of Freq, Gain, or Q values. Committing a numeric entry saves and redraws the canvas and icon row immediately. The row's background is transparent so it no longer overlaps the audio band-plan strip at the bottom of the canvas above it.	Located in the floating editor only. Implemented by ClientEqParamRow. Numeric entry via right-click menu was added in v26.5.2.1 to persist edits immediately (issue #2655).
Filter cutoff guide lines (TX / RX)	Dashed yellow vertical lines overlaid on the canvas at the radio's current TX low/high filter cutoff (TX tile) or RX passband edges (RX tile). Hovering near a line changes the cursor to a horizontal-resize arrow. Dragging a line in the editor moves the radio's corresponding filter cutoff in real time.	Dragging the TX cutoff guides emits cutoffsDragRequested(Tx, lo, hi), which MainWindow forwards to TransmitModel. Dragging the RX guides writes to the active SliceModel. Pass 0 for an edge to suppress that guide. RX passband guides are cached internally; switching from TX back to RX restores the correct RX guides automatically. The applet tile displays the guide lines as a visual reference; dragging is available in the floating editor only.
Output Fader	Vertical combined fader + level meter on the right edge of the floating editor. Drag to set post-EQ master gain; scroll wheel adjusts in 0.5 dB steps; double-click resets to 0 dB. Range: -36 to +12 dB. The level bar behind the handle shows the smoothed post-EQ peak in real time with the same green-amber-red gradient as the Tube level meter. Click the numeric value display at the bottom to edit it directly — type a dB value and press Enter to commit (clamped to range). Press Escape to cancel editing. Located in the floating editor only — not in the docked applet tile.	Persisted separately per path: ClientEqTxMasterGain / ClientEqRxMasterGain. Tooltip: "Output gain (dB). Drag to set, wheel for fine step, double-click to reset to 0 dB." The numeric value display is a QLineEdit that looks identical to a label until focused. On focus, it shows the bare number with a cyan border; type a value and press Enter or click away to commit. The value is clamped to the -36 to +12 dB range.

Bypass is handled from the CHAIN widget, not from inside the editor. See Bypass the EQ stage from the chain.

Performance and caching

The EQ canvas uses two retained pixmap layers (background and response) to avoid redrawing static grid lines, labels, and EQ curves on every analyzer update. These layers are invalidated only when the relevant state changes (widget size, device pixel ratio, font, filter cutoffs, or EQ response parameters). The response layer caches the full EQ band state, filter family, sample rate, active band count, reference curve preset, selection, and filled-region visibility. Each layer is bounded to a maximum of 32 MB of pixel data; canvases larger than this threshold are rendered directly without caching to preserve fidelity. The live FFT analyzer and peak-hold trace are drawn on top of these cached layers every 40 ms (25 Hz refresh), and the visible FFT updates counter accumulates for performance statistics.

Reference Curve Presets

The reference curve preset feature overlays a visual target curve on the EQ canvas, allowing you to shape your parametric EQ bands toward the frequency response of classic microphones or audio standards. The curve is drawn as a semi-transparent amber line behind your EQ band curves. Selecting a preset does not change the audio processing — it is a visual guide only.

Available reference curve presets:

Preset	Description
Off	No reference curve shown.
AT&T 1959	The canonical Bell Labs "optimum transmission frequency response for speech" target. Peak +5 dB at 2.5 kHz, rolls off below 300 Hz and above 3.4 kHz.
Heil DX	Bob Heil's published recommendation for maximum talk power in pile-ups. Sharper +6 dB peak at 2.7 kHz with more aggressive low-cut than AT&T 1959.
Astatic D-104	The classic "lollipop" crystal microphone response. Extremely peaky presence boost around 3 kHz with deep low-end rolloff.
Shure 444	Classic broadcast-style desk microphone with broader response and gentler presence boost — the smoothest of the legendary mic curves.
Heil HC-5	Modern dynamic SSB microphone target shape. Mid-presence boost peaks at 3 kHz at +5 dB.

To select a reference curve: 1. Open the floating editor for the desired path (TX or RX). 2. Click the Ref combo box in the editor header strip. 3. Select the desired preset from the dropdown list. 4. The semi