User`s guide

3 Working with Signals
3-16
Sample Rates and Frame Rates
Sample rates are an important issue in most DSP models, especially in systems
incorporating rate conversions. Fortunately, in most cases, when you build a
Simulink model you only need to worry about setting sample rates in the source
blocks, such as Signal From Workspace; Simulink automatically computes the
appropriate sample rates for all downstream blocks.
Nevertheless, it is important to become familiar with the concepts of “sample
rate” and “frame rate” as they apply in the Simulink world. The next sections
cover the following important topics:
•“Sample Rate and Frame Rate Concepts”
•“Inspecting Sample Rates and Frame Rates”
•“Converting Sample Rates and Frame Rates”
•“Changing Frame Status”
Sample Rate and Frame Rate Concepts
The input frame period (T
fi
) of a frame-based signal is the time interval
between consecutive vector or matrix inputs to a block. This interval is what
the Probe block displays when you connect it to a frame-based input line.
Similarly, the output frame period (T
fo
) is the time interval at which the block
updates the frame-based vector or matrix value at the output port. This
interval is what the Probe block displays when you connect it to a frame-based
output line. (See “Inspecting Sample Rates and Frame Rates” on page 3-17 for
more about using the Probe block.)
In contrast, the sample period, T
s
, is the time interval between individual
samples in a frame, which is necessarily shorter than the frame period when
the frame size is greater than 1. The sample period of a frame-based signal is
the quotient of the frame period and the frame size, M.
More specifically, the sample periods of inputs (T
si
) and outputs (T
so
) are
related to their respective frame periods by
T
s
T
f
M⁄=
T
si
T
fi
M
i
⁄=
T
so
T
fo
M
o
⁄=