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Live monitoring

Before committing to a recording it helps to see the incoming signal — check levels, watch for clipping, confirm a mode is where you expect. The web logger gives you two live views of the input: a persistent mini-monitor that follows you across every stage, and a full-screen Live oscilloscope.

Both run against whichever source is active — a browser soundcard or a bridged soundcard/NI device — and both compute their spectra in the browser in real time.

The mini-monitor

In the wide layout a Monitor panel is docked at the foot of the dataset tray, so it stays visible no matter which stage you are on.

  • When off it shows a ▶ Start button.
  • When running it shows a compact time trace, per-channel level bars with a latching CLIP indicator, an ⤢ button to expand into the full Live stage, a ▾ to collapse the body, and a Stop button.

The monitor is persistent — it is not stopped automatically when you change stages. Start it once and it keeps running until you stop it (or close the tab).

Narrow layout

On a narrow window the tray collapses to a compact rail and the docked mini-monitor is not shown; use the Live stage instead.

The Live stage

Open Live (or press ⤢ on the mini-monitor) for the full oscilloscope. Its controls live in the Live card:

  • Start Monitor → ⏸ Pause / ▶ Resume and Stop while running.
  • display — Stacked (one lane per channel) and Auto Y (autoscale the amplitude axis, on by default).
  • view time — the time window shown: 50 / 100 / 200 / 500 ms or 1 s, or custom… for any window from 20 ms to 5 s.

Inside the plot region a bar of chips toggles the panes:

  • T time — the oscilloscope trace.
  • F freq — the live spectrum (see below).
  • L levels — the per-channel level bars with the CLIP latch.
  • P pause — freeze the display.

Live spectrum: FFT or Welch PSD

The F freq pane has its own controls:

  • spectrum — FFT (a per-frame amplitude spectrum) or PSD (an averaged Welch power spectral density).
  • fft axes — magnitude dB / lin, and frequency lin f / log f.
  • fft freq — Full (DC to Nyquist) or Range (enter a min/max band).

In PSD mode two more controls appear: averages (1× to 16×, how many overlapping Welch segments to average — steadier but slower to respond) and smoothing (off / low / high — exponential smoothing across frames). PSD is displayed in dB/Hz (or linear u²/Hz).

The FFT/PSD is a windowed (Hann) transform computed in the browser every frame, so it works identically whether the source is Web Audio or the bridge.

Levels and clipping

The level bars fill green → amber → red with the signal peak. The CLIP pill latches as soon as any channel's peak reaches 0.95 of full scale, and stays lit until you click it (or restart the monitor) — so you never miss a brief clip that happened while you were looking elsewhere. If CLIP trips, reduce the input level or (on NI) widen the voltage range before recording.

Full scale is whatever the device's own rail is, not a fixed 1.0. On an NI card it is the input range you set (VmaxNI, e.g. ±5 V), so a 3 V peak reads 60 % and does not trip CLIP; on a calibrated audio jack it is the full-scale voltage derived from the stated gain; on Web Audio and an uncalibrated jack the samples are a bare 0–1 fraction and full scale is 1.0. The bridge reports the rail with every configure, so the meters and the capture-time clip warning (acquisition.log_data, which checks against 95 % of the same rail) always agree. Hover a bar to see the percentage, and the reading in volts where the rail has a voltage meaning.

Tips

  • Use Live to set levels first, then switch to Acquire to record — the mini-monitor keeps running so you can watch levels during setup.
  • Watch coherence in the TF stage after recording, but catch gross problems (clipping, dead channels, wrong device) live — it is much cheaper than re-recording.

Next: Analysis views.