User`s guide

4 DSP Operations
4-12
Note that the three-block sequence of FFT, Complex to Magnitude-Angle, and
Vector Scope could be replaced by a single Spectrum Scope block, which
computes the magnitude FFT internally.
Other blocks that compute the FFT internally are the blocks in the Power
Spectrum Estimation library. See “Power Spectrum Estimation” on page 4-15
for more information about these blocks.
Example: Using the IFFT Block
In the model below, the Sine Wave block again generates two frame-based
sinusoids, one at 15 Hz and the other at 40 Hz. The sinusoids are summed
point-by-point to generate the compound sinusoid
which is transformed to the frequency domain using an FFT block. The
frequency-domain signal is then immediately transformed back to the time
domain by the IFFT block, and the difference between the original time-domain
signal and transformed time-domain signal is plotted on the scope.
To build the model, make the following parameter settings (leave unlisted
parameters in their default settings):
•In the Sine Wave block, set:
-
Amplitude = 1
- Frequency = [15 40]
- Phase offset = 0
- Sample time = 0.001
- Samples per frame = 128
•In the Matrix Sum block, set Sum along = Rows.
•In the FFT block, set
Output in bit-reversed order =
•In the IFFT block, set:
u 30πt() 80πt()sin+sin=