User Manual
3.4 Setting FFT Analysis Conditions
59
Description See "Trigger Modes and Averaging" (⇒ p. 60)
When averaging time-domain waveform values
Waveforms are acquired and averaged within the time domain. After averaging, FFT cal-
culation is performed.
When the trigger mode is [Auto]: Data is acquired when the START key is pressed, even
if trigger criteria are not met after a certain interval. So if averaging is applied to an asyn-
chronous signal, the resulting data is meaningless.
Synchronous signals have better SNR (signal-to-noise ratio) and are more suitable for
analysis.
When averaging spectrum values
Acquired data is first subject to FFT analysis. After analysis, averaging is performed within
the frequency range, and the result is displayed. This differs from time-domain averaging
in that averaging can be performed without trigger synchronization. However, if the char-
acteristics of the input waveform allow triggering, using the trigger for synchronization is
recommended.
Spectrum peak hold
After performing FFT calculations on the acquired waveform, peak values are retained
(held) and displayed within the frequency range.
FFT Analysis Modes and Averaging _______________________________
z: Settable, ×: Unsettable, O: Partially settable
Analysis Mode
Averaging
Waveform Averaging Spectrum Averaging
Simple Exponential Simple Exponential Peak Hold
OFF
×××××
Storage Waveform
zz×××
Linear Spectrum
zz
O
*2
O
*2
O
*2
RMS Spectrum
zz
O
*2
O
*2
O
*2
Power Spectrum
zzzzz
Power Spectrum Density *1
zzzzz
Auto-correlation Function
zzzzz
Histogram
zz×××
1/1 Octave Analysis *1
zzzzz
1/3 Octave Analysis *1
zzzzz
Transfer Function
zz
O
*2
O
*2
O
*2
Cross Power Spectrum
zz
O
*2
O
*2
O
*2
Cross-correlation Function
zzzzz
Impulse Response
zzzzz
Coherence Function
××zz ×
Phase Spectrum
zz×××
Power Spectrum Density (LPC) *1
zz×××
*1. Not available for external sampling
*2. Not available when the y axis is real (linear) or imaginary (linear), or for Nyquist plots