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Trans for ma tion. The win dowed au dio data is trans formed by the FFT.
This re sults in an ar ray of points de scrib ing the mag ni tude and phase of
each fre quency in the au dio sig nal.
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Dis play. The con trol soft ware fetches the trans formed au dio data and
graphs it. Be cause the num ber of trans formed points is typ i cally larger
than the num ber of points in the graph, a peak-picking method is used to
en sure that peaks in the fre quency data are not missed.
For more in for ma tion, see Ap pen dix C of the 2700 Se ries User’s Man ual.
Setting up an FFT
Click New Test and open the Dig i tal An a lyzer panel. Af ter a New Test, the
Dig i tal An a lyzer panel de faults to None as its an a lyzer. To switch to the Spec -
trum An a lyzer, click the down ar row next to the An a lyzer field at the top of
the Dig i tal An a lyzer panel. From the list, choose FFT spec trum an a lyzer
(fft). The panel changes to dis play the anal y sis tool.
Panel Fields
There are two peak mon i tors near the top of the panel, one for each of the
ste reo chan nels. These me ters give an in di ca tion of the pres ence of sig nal at
the FFT in put.
Be low the peak me ters is an ar ray of fields for con fig ur ing the an a lyzer.
Here, we will use the de fault set tings. For more de tails on the set tings, see
Chap ter 11 of the 2700 Se ries User’s Man ual.
Time vs. Frequency
As men tioned, the FFT spec trum an a lyzer can dis play au dio sig nals in the
time do main and the fre quency do main. The choice of do main is de ter mined
by the Source 1 field on the Sweep panel. If it is set to Fft.FFT Time, a time
The FFT Spectrum Analyzer Chapter 5: Quick Guides
Getting Started with Your 2700 Series Instrument 47
Figure 28. FFT Spectrum Analyzer panel.
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