User`s guide

Sample Rates and Frame Rates
3-31
In this case, based on the input frame size (256) and period (12.8), the Vector
Scope block calculates the original signal’s sample period to be 0.05 seconds
(12.8/256), which is wrong. As a result, the spectral peaks appear at the
incorrect frequencies, 2 Hz and 4 Hz rather than 1 Hz and 2 Hz.
The problem is that the zero-pad operation performed by the Magnitude FFT
block halves the sample period of the sequence by appending 128 zeros to each
frame. The Vector Scope block, however, needs to know the sample period of
the original signal. The problem is easily solved by changing the
Sample time
of original time series
setting in the Axis properties panel of the Vector
Scope block to the actual sample period of
0.1. The plot generated with this
setting is identical to the first Vector Scope plot above.
In general, be aware that when you do zero-padding or overlapping buffering
you are changing the sample period of the signal. As long as you keep this in
mind, you should be able to anticipate and correct problems like the one above.
Changing Frame Status
The frame status of a signal refers to whether the signal is sample-based or
frame-based. In a Simulink model, the frame status is symbolized by a single
line, →, for a sample-based signal and a double line, ⇒, for a frame-based
signal.
In most cases, the appropriate way to convert a sample-based signal to a
frame-based signal is by using the Buffer block, and the appropriate way to