User`s guide

3 Working with Signals
3-4
The following sections provide definitions for a number of terms commonly
used to describe the time and frequency characteristics of discrete-time signals,
and explain how these characteristics relate to Simulink models:
•“Time and Frequency Terminology”
•“Discrete-Time Signals in Simulink”
Time and Frequency Terminology
A number of different terms are used to describe the characteristics of
discrete-time signals found in Simulink models. These terms, which are listed
in the table below, are frequently used in Chapter 5, “DSP Block Reference,” to
describe the way that various blocks operate on sample-based and frame-based
signals.
Term Symbol Units Notes
Sample period T
s
T
si
T
so
,
Seconds The time interval between consecutive
samples in a sequence, as the input to a block
(T
si
) or the output from a block (T
so
).
Frame period T
f
T
fi
T
fo
Seconds The time interval between consecutive frames
in a sequence, as the input to a block (T
fi
) or
the output from a block (T
fo
).
Signal period T Seconds The time elapsed during a single repetition of
a periodic signal.
Sample rate, or
Sample frequency
F
s
Hz (samples
per second)
The number of samples per unit time,
F
s=
1/T
s
.
Frequency f Hz (cycles
per second)
The number of repetitions per unit time of a
periodic signal or signal component, f = 1/T.
Nyquist rate Hz (cycles
per second)
The minimum sample rate that avoids
aliasing, usually twice the highest frequency
in the signal being sampled.
Nyquist frequency f
nyq
Hz (cycles
per second)
Half the Nyquist rate.