The Video Bandwidth Filter, or VBW, is a low pass filter that is applied to each frequency bin before sending the appropriate amplitude value to the display. It effectively averages (smooths) the signal and can be used to help minimize the effects of noise on the displayed trace. It is especially useful when dealing with low power signals that are close to the noise floor of the instrument.

The two pictures below are comparing a 20MHz sine wave input captured at a VBW of 100kHz and 1kHz respectively. You can see how the VBW smooths the trace and makes it easier to see the true signal.

Note that decreasing the VBW setting can increase the sweep time

Many analyzers also provide the ability to average a number of traces when using an Averaging Detector like RMS or Voltage.

Averaging traces has a similar effect to lowering the VBW setting as shown below, but this technique can require successive scans which can lead to a longer total test time.