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Averaging successive measurements usually improves measurement accuracy. Averaging usually is performed on measurement results or on individual spectra but not directly on the time record.

You can choose from among the following common averaging modes:

• RMS averaging
• Vector averaging
• Peak hold

RMS Averaging

RMS averaging reduces signal fluctuations but not the noise floor. The noise floor is not reduced because RMS averaging averages the energy, or power, of the signal. RMS averaging also causes averaged RMS quantities of single-channel measurements to have zero phase. RMS averaging for dual-channel measurements preserves important phase information. RMS-averaged measurements are computed according to the following equations.

FFT spectrum
power spectrum
cross spectrum
frequency response

where X is the complex FFT of signal x (stimulus), Y is the complex FFT of signal y (response), X* is the complex conjugate of X, Y* is the complex conjugate of Y, and is the average of X, real and imaginary parts being averaged separately.

Vector Averaging

Vector averaging eliminates noise from synchronous signals. Vector averaging computes the average of complex quantities directly. The real part is averaged separately from the imaginary part. Averaging the real part separately from the imaginary part can reduce the noise floor for random signals because random signals are not phase coherent from one time record to the next. The real and imaginary parts are averaged separately, reducing noise but usually requiring a trigger.

FFT spectrum
power spectrum
cross spectrum
frequency response

where X is the complex FFT of signal x (stimulus), Y is the complex FFT of signal y (response), X* is the complex conjugate of X, and is the average of X, real and imaginary parts being averaged separately.

Peak Hold

Peak hold averaging retains the peak levels of the averaged quantities. Peak hold averaging is performed at each frequency line separately, retaining peak levels from one FFT record to the next.

FFT spectrum
power spectrum

where X is the complex FFT of signal x (stimulus) and X* is the complex conjugate of X.

Weighting

When performing RMS or vector averaging, you can weight each new spectral record using either linear or exponential weighting.

Linear weighting combines N spectral records with equal weighting. When the number of averages is completed, the analyzer stops averaging and presents the averaged results.

Exponential weighting emphasizes new spectral data more than old and is a continuous process.

Weighting is applied according to the following equation.

where X_i is the result of the analysis performed on the i^th block, Y_i is the result of the averaging process from X₁ to X_i, N = i for linear weighting, and N is a constant for exponential weighting (N = 1 for i = 1).