Cross Spectrum (Channel Quality)

Menu Path: Trace > Data > Cross Channel NxM > NxM > Cross Spectrum where N and M are channel numbers

Cross Spectrum trace data (also called cross power spectrum) is a two-channel measurement. Cross spectrum is seldom used as a separate measurement, but is used internally by the VSA to compute other measurements such as transfer function and Coherence.

The cross spectrum, Gxy, is defined as taking the FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. of two signals separately and multiplying the results together, as follows:

The exact computation used by the VSA depends on the type of average used:

If the average is:	the VSA uses this formula:
None	A
Time	A
Time exponential	A
rms	B
rms exponential	C
peak hold/continuous peak hold	cross spec. unavailable

Term	Definition
L	number of averages
linspec,N	linear spectrum channel N
xavg	(1/L) * new + ((L-1)/L)* old
conj	conjugation