These setting control how the spectral data is averaged.
Free Run (blocks) - this is the default mode and updates the analyzer each time a new FFT block of data is computed. In this mode the average block size directly determines how many spectra blocks are averaged together to compute a moving average. For instance, if the averaging block size is set to 4, the spectrum currently displayed is a moving average of the previous 4 traces.
If the signal you are measuring is rapidly changing in frequency, a low averaging block size should be used. Use a high block size to "dig" out a steady state signal buried in a noisy background.
Setting the averaging size to "infinite" causes the program to average successive spectral traces continuously. Stopping and restarting the processor will reset the average.
Sound Level Meter (SLM) - this mode sets the averaging algorithm to match that of a standard Sound Level Meter (SLM). The average speed controls the spectral averaging period and decay time as follows:
Off - no averaging is performed.
Fast - computes a running average with a decay rate of 32 dB/sec.
Medium - computes a running average with a decay rate of 20 dB/sec.
Slow - computes a running average with a decay rate of 4 dB/sec.
Forever - accumulates the data for as long as the analyzer is running.
Exponential averaging should be used when the Sound Level Meter mode is selected.
Exponential - this method produces an average where the most recently acquired spectra have more influence on the average than older ones. If you were to suddenly shut off the input signal, the decay rate will follow an exponential curve. Exponential averaging should be used when the Sound Level Meter mode is selected.
Linear - this method is a straight linear average of the spectra over time. Each spectra block contributes equally to the average. This type of averaging is also known as "stable averaging"
Vector - this method performs a complex (vector) average of successive spectra over time. Because vector averaging includes the phase component in the computation, triggering must be employed if meaningful results are to be expected. This type of averaging is also known as "synchronous averaging".
Exponential averaging is the default as it is more computationally efficient.
In both the Real-Time and Post-Processing modes, the averaging speed/block size can be modified while processing by using the "Avg" control on the toolbar. The active channel corresponds to the plot which has the "focus" (its title bar is highlighted).
See also: Peak Hold