Threshold (Spectrogram / 3D Map)
The parameter specifies the threshold for a spectrogram or cumulative history applied to the active trace. This feature is useful for removing noise-floor clutter from the spectrogram or transients from cumulative history.
When a threshold is specified, the VSA shows colors for amplitude/density values at or above the threshold; below the threshold, the VSA uses the bottom color in the color bar for spectrograms or the trace background color for cumulative history.
The threshold is specified as a percentage of the height of the color bar. Thus, with a threshold of 50%, the VSA maps the color map to the upper half of the color bar. Note that a threshold of 100% the trace shows nothing because the amplitude/density value never exceeds the threshold.
The following illustration shows the spectrogram color bar with threshold set at 0%, 25%, 50% and 75% (from left to right). The cumulative history color bar is the same except the bottom color will be the trace background color.
The next illustration shows two spectrogram traces of a pulsed signal. The trace on the left has threshold set at 0%. For the trace on the right, threshold was set to 50%. The threshold setting of 50% removed the noise that cluttered the trace on the left.
