Metric Halo SpectraFoo - Manual (Page 28)

Instruments
28
Figure 3.10: Spectragraph Second Traces pop-up
Accumulation modes
SpectraFoo’s underlying FFT generates more data than can be displayed on screen at once. The way that this
data is treated when the system computes the trace is called the accumulation mode. SpectraFoo provides two
accumulation modes that you can choose using the Spectragraph Controls window:
Figure 3.11: Accumulation Mode pop-up
1. When the Accumulation Mode is set to White Noise is Flat, the Spectragraph shows the maximum
power of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the
effect displaying white noise (or noise that has an equal amount of power at each frequency) as a flat
line. This mode is traditionally used when the frequency scale of the graph is linear.
2. When the Accumulation Mode is set to Pink Noise is Flat, the Spectragraph shows the sum of the power
of all of the spectral lines in the FFT that fit into each point in the displayed trace. This has the effect of
displaying pink noise (or noise that has an equal amount of power in each octave) as a flat line. This
mode is traditionally used when the frequency scale of the graph is logarithmic and corresponds to the
type of display available on a traditional RTA.
The figures below show the results of the two weighting accumulation modes with the two different kinds
of noise.