Output Level Meter overview¶
The Output Level Meter is a vertical dB meter that shows the smoothed post-processing peak level of an audio stage. It gives you a continuous visual and numeric read of how close the output signal is to clipping, so you can set drive and output levels without guessing.
How it works¶
The meter receives peak level updates from the audio engine and applies fast-attack / slow-release ballistics before displaying the result. When the incoming level rises, the smoothing factor is 0.6 (fast attack), so the bar reacts quickly to peaks. When the level falls, the smoothing factor is 0.08 (slow release), so the bar decays gradually. This matching ballistic behavior is shared with the EQ output fader meter, so all meters in AetherSDR feel visually consistent.
The meter is visible inside the Tube applet's frameless editor, to the right of the saturation curve. Open it by double-clicking the TUBE stage in the chain widget. The same ballistics are also used by the EQ editor's Output Fader meter.
No settings are persisted for this widget. It has no interactive controls; all elements are read-only indicators.
Numeric readout throttling¶
The numeric dB readout below the bar updates at 10 Hz (100 ms intervals) even though the level bar animates on every paint event. This keeps the digits stable and readable while the bar continues to show smooth level changes. The readout displays -inf when the smoothed peak level is below approximately −59.5 dB, and re-formats to a signed dB value with one decimal place otherwise.
Theme support¶
The level bar's fill color is drawn from the color.meter.bar.fillGradient theme token. When you modify this token in the Theme Editor, the meter updates immediately without needing to restart AetherSDR. The gradient is a 5-stop linear gradient that maps from bottom to top of the full bar strip. As the signal level rises, the visible fill grows upward through the gradient, so the color at the bottom of the fill always matches what that position in the gradient would show.
What each control does¶
| Element | Description | Range / Values |
|---|---|---|
| Header label | Identifies what the meter is measuring. The Tube applet sets this to OUT. An empty string hides the header. |
Any short string; default OUT |
| Level bar | Gradient-filled vertical bar showing the smoothed peak level. Fills from the bottom up, proportional to the current dB value. The fill gradient is themed via color.meter.bar.fillGradient. |
−60 dB (bottom) to 0 dB (top) |
| dB scale ticks | Static reference grid to the left of the bar with labeled tick marks. | 0, −6, −12, −20, −40 dB |
| Numeric readout | Displays the smoothed peak as a signed dB value to one decimal place, centered below the bar. Updates at 10 Hz. Shows -inf when the level is below approximately −59.5 dB. |
-inf or a value in the form +/-XX.X dB |
Level bar color¶
The fill color changes with level to give an immediate sense of headroom. The exact gradient stops are defined by the color.meter.bar.fillGradient theme token. The default gradient produces:
| Color | Level range | Meaning |
|---|---|---|
| Green | −60 dB to −12 dB | Normal operating level |
| Lime | −12 dB to −6 dB | Moderate level |
| Amber | −6 dB to −3 dB | Approaching clipping |
| Red | Above −3 dB | 3 dB or less from clipping |
Tips¶
- Watch for amber or red on the level bar while adjusting the Tube applet's Drive or Output knobs. Red means you have 3 dB or less of headroom before clipping.
- The slow-release ballistics (alpha 0.08) mean the bar holds elevated readings briefly after a peak. This is intentional — it lets you catch transients that would otherwise disappear before you notice them.
- The numeric readout may appear to "lag" behind the level bar by up to 100 ms. This is normal — the bar animates smoothly while the digits update at a fixed 10 Hz rate for readability.
- To change the meter's fill colors, edit the
color.meter.bar.fillGradienttoken in the Theme Editor. The meter re-renders immediately to show your changes.