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Signal modulation

Signal modulation, or sigmod, is an advanced, experimental render-only display feature that adds a color-coded overlay to a rendered trace based on a derived property of that signal. The original waveform remains visible, so sigmod acts as an extra visual layer rather than a separate plot.

For example, here we set the top EEG trace ( which is also narrowband filtered to the 0.5 - 1 Hz range ) to reflect the phase of the same channel also filtered to the same 0.5 - 1 Hz interval, using a red-white-blue palette. Below is an ECG trace, with is colored with respect to the amplitude of that same ECG between the 8-25 Hz range, with a different pallete, effectively visually highlighting the R peaks:

imgs/v2/sigmod-1.png

A modulation is based on one signal but can be applied to other signals, or differently filtered versions of the same singal: for example, here is the same modulation but applied to the 0.3 - 35 Hz filtered EEG trace - for example, this may provide visual indicators of spindle-slow oscillation coupling:

imgs/v2/sigmod-2.png

Because sigmod depends on rendered data, it does not appear in the simple unrendered view. It is configured through the Configuration file format using [mod], [pal], and mod=... entries.

Modulation types

The current modulation types are:

  • raw : color the trace from the source signal itself

  • amp : color the trace from amplitude-like information, optionally in a chosen frequency band

  • phase : color the trace from phase-like information, optionally in a chosen frequency band

Why use it

Typical reasons to use sigmod are:

  • to make band-limited amplitude changes easier to spot while still viewing the original waveform

  • to visualize phase structure without replacing the trace with a separate plot

  • to highlight only the strongest modulation bins with threshold-like palettes

Configuration

The conceptual setup is:

  1. define one or more [mod] entries
  2. optionally define a custom [pal] palette, or use a built-in palette
  3. attach the modulation to a signal in [sig] with mod=<mod_label>,<pal_label>
  4. render the signal view

For the full syntax, built-in palette reference, and examples, see the Configuration page.